Clutch in = idle surge. Why? (Bouncy idle related)
12-05-08 | 01:51 AM
#1
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From: Seattle, WA
Clutch in = idle surge. Why? (Bouncy idle related)
Tried to search and found other people asking similar question, but no posts containing the answers.
Basically I'm still troubleshooting bouncy idle, but that's not the point. The point is when I have the idle bounce up and down, if I push in the clutch, RPM goes up by about a 1000, and becomes steady at that mark. Releasing the clutch takes RPM back to low bouncy idle.
Why does that happen? Am I correct in assuming that de-clutching the motor releases the extra friction and load caused by transmission, thus allowing it to surge up with ease, because BAC still thinks the motor is at idle and continues to compensate with extra air? Although I don't understand why it would be steady instead of just bouncing at a higher RPM range.
Or is there some other reason?
Basically I'm still troubleshooting bouncy idle, but that's not the point. The point is when I have the idle bounce up and down, if I push in the clutch, RPM goes up by about a 1000, and becomes steady at that mark. Releasing the clutch takes RPM back to low bouncy idle.
Why does that happen? Am I correct in assuming that de-clutching the motor releases the extra friction and load caused by transmission, thus allowing it to surge up with ease, because BAC still thinks the motor is at idle and continues to compensate with extra air? Although I don't understand why it would be steady instead of just bouncing at a higher RPM range.
Or is there some other reason?
12-05-08 | 08:38 AM
#2
the bouncing idle may be caused my a misadjusted or faulty tps. the high idle can be caused my a number of things. the throttle body shafts could be gummed up, not allowing the throttle plates to fully close. the bacv may be faulty, you may have a vacuum leak...heck, someone may have tampered with the idle adjust screw. in some cases a high idle is caused by the coolant temp switch located on the rear of the water pump housing.
12-05-08 | 09:14 PM
#4
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Yeah, it's GSL-SE of course.
Are there any inputs or sensors that would change idle management based on clutch position?
Oh, and mazdaverx, I'm not asking why it's bouncing. I'm asking why it's affected by the clutch position when it does, while not being affected when it's steady.
Are there any inputs or sensors that would change idle management based on clutch position?
Oh, and mazdaverx, I'm not asking why it's bouncing. I'm asking why it's affected by the clutch position when it does, while not being affected when it's steady.
12-06-08 | 11:39 AM
#7
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From: knoxville, tn
Whats does the idle do in neutral? Most problems with the gsl-se idle are centered around either a dirty throttle body or a TPS out of adjustment. Read the FAQ link that was posted above and also search for any posts by Longduck. Good luck.
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12-06-08 | 02:32 PM
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From: Seattle, WA
Sigh...
I don't need help solving the idle problem. I've already been linked to FAQ and all of longduck's posts many times, and I've read all of them weeks ago. That's not what I'm asking about.
I want to know idle's relation to clutch/transmission. And yes, in neutral obviously, since I'm only talking about idle.
In neutral. Idle bouncing up and down between 800-1200 (typical idle issue). Push in the clutch pedal. Idle revs up to 2000 and stays there. Why? Why wouldn't it just keep bouncing at the same 800-1200?
Exactly. Yet somehow it happens. I don't understand why.
Seems I'm not the only one it's happened to, either.
I was driving down the street, the car was running fine. Then all of the sudden I pressed in the clutch and the idle went up to about 2100-2200 rpms. It was missing too. I shut the car off, waited a second, and then started it back up again. With the clutch out it didn't miss but the idle jumps in between 1300 and 1600 rpms. As soon as pushed the clutch in it jumped right back up to 2200 and started missing. When accelerating it seems okay, but the throttle is really touchy and pressing the pedal down just a little makes the car miss and jerk.
I don't need help solving the idle problem. I've already been linked to FAQ and all of longduck's posts many times, and I've read all of them weeks ago. That's not what I'm asking about.
I want to know idle's relation to clutch/transmission. And yes, in neutral obviously, since I'm only talking about idle.
In neutral. Idle bouncing up and down between 800-1200 (typical idle issue). Push in the clutch pedal. Idle revs up to 2000 and stays there. Why? Why wouldn't it just keep bouncing at the same 800-1200?
Exactly. Yet somehow it happens. I don't understand why.
Seems I'm not the only one it's happened to, either.
I was driving down the street, the car was running fine. Then all of the sudden I pressed in the clutch and the idle went up to about 2100-2200 rpms. It was missing too. I shut the car off, waited a second, and then started it back up again. With the clutch out it didn't miss but the idle jumps in between 1300 and 1600 rpms. As soon as pushed the clutch in it jumped right back up to 2200 and started missing. When accelerating it seems okay, but the throttle is really touchy and pressing the pedal down just a little makes the car miss and jerk.
Last edited by Whisper; 12-06-08 at 02:39 PM.
12-06-08 | 05:31 PM
#11
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From: Muncie, IN
I don't see how there would be any ties whatsoever to vacuum with the clutch, however maybe you're overlooking something else that is happening when you're pressing in the clutch.
I'm not familiar with the GSL-SE at all, but I wouldn't imagine any vacuum lines would be involved in the clutch setup. It does, however, sound like you've got a vacuum leak somewhere.
I'm not familiar with the GSL-SE at all, but I wouldn't imagine any vacuum lines would be involved in the clutch setup. It does, however, sound like you've got a vacuum leak somewhere.
12-06-08 | 06:07 PM
#12
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No you didn't read the FAQ's because this is explaining exactly what your experiencing....
Pull the vacuum lines from your distributor and block them off. Then try dumping the clutch in neutral, the same thing will happen if your disconnect your tps. I bet the idle will not jump up. If you open the hood and have someone press the clutch you can hear the green solenoid click on and off advancing the idle bumping it up. Put your finger on it too and you can feel it click.
Make sure your tps and V&V solenoids are plugged in. I say properly adjust your TPS by warming up your car, turning it off and moving key into the last position, disconnecting your vent and vacuum solenoids (one plug), THEN adjust you TPS. If that doesn't work then while the car is running have someone press the clutch and turn the TPS screw CW or CCW till the idle falls. Any downward pressure on the screw will change the position of the throttle plates so oh so delicately turn the screw. If all else fails ohm out the tps, should be 1kohm closed to 5kohm open. Best of luck.
PROBLEM #7: Idle speed "hangs up" at around 1100 rpm, but suddenly drops back to normal (as if the ignition was momentarily turned off) when the clutch pedal is released. Another way to drop the idle back to normal is to place an electrical load on the engine (like holding the power window switches down when the windows can't go any further).
Felix Miata posted a solution to this one, and I will paraphrase it here.
Adjusting the engine's spark advance can alter the idle speed. Within limits, the more advanced the spark, the faster the idle. Spark advance on the GSL-SE engine is controlled in part by the EGI system, which supplies vacuum to the distributor when the spark needs to be advanced. This occurs when the engine speed increases beyond the range of 1,000 to 1,200 rpm. When the Throttle Position Sensor senses that your foot is off the gas, the EGI system cuts the vacuum supply, and the spark timing suddenly drops to its retarded setting. (This, by the way, is a function of the green valve below and to the left of the BAC valve. That's why they call it the Vacuum Control Solenoid Valve.) As the engine ages, the throttle shafts get a little loose, and even though you have adjusted the TPS by the book, the throttle shafts may be shifting position a little, not allowing the TPS to get to the point where it signals the EGI that the car is supposed to be idling. The EGI system fails to retard the spark, and the idle hangs up until something else (releasing the clutch, or putting an electrical or mechanical load on the engine) persuades the EGI system to cut vacuum to the distributor. You can watch this happening with a timing light.
One fix for this is to get a new Throttle Body, but that would be costly. Better to tweak the TPS so that it compensates for the wear in the throttle shafts. When adjusted according to the manual, the TPS will show proper adjustment over a range of a half-turn of the screw or so. Favor the adjustment toward the screw being turned clockwise. If this doesn't work, Felix suggests readjusting the TPS, but not by the manual.
He says to cause the idle to hang up by raising engine speed above 2,000 rpm. Do this with the gas pedal to duplicate the actual driving condition. Don't touch the throttle shaft. Hold your engine speed above 2000 rpm for several seconds and release. This should hang the idle up. Go to the TPS and delicately--without any downward pressure--turn the adjusting screw slowly clockwise until the idle speed falls.
You can now shut the engine down and (using the standard procedure) check the TPS. You should get the proper reading. As a double check, with just a little pressure with your finger on the screw with the test light pair hooked up, the second light will light, and go right back off when you let go. Refer to the section on adjusting the TPS for details on the adjustment.
Felix Miata posted a solution to this one, and I will paraphrase it here.
Adjusting the engine's spark advance can alter the idle speed. Within limits, the more advanced the spark, the faster the idle. Spark advance on the GSL-SE engine is controlled in part by the EGI system, which supplies vacuum to the distributor when the spark needs to be advanced. This occurs when the engine speed increases beyond the range of 1,000 to 1,200 rpm. When the Throttle Position Sensor senses that your foot is off the gas, the EGI system cuts the vacuum supply, and the spark timing suddenly drops to its retarded setting. (This, by the way, is a function of the green valve below and to the left of the BAC valve. That's why they call it the Vacuum Control Solenoid Valve.) As the engine ages, the throttle shafts get a little loose, and even though you have adjusted the TPS by the book, the throttle shafts may be shifting position a little, not allowing the TPS to get to the point where it signals the EGI that the car is supposed to be idling. The EGI system fails to retard the spark, and the idle hangs up until something else (releasing the clutch, or putting an electrical or mechanical load on the engine) persuades the EGI system to cut vacuum to the distributor. You can watch this happening with a timing light.
One fix for this is to get a new Throttle Body, but that would be costly. Better to tweak the TPS so that it compensates for the wear in the throttle shafts. When adjusted according to the manual, the TPS will show proper adjustment over a range of a half-turn of the screw or so. Favor the adjustment toward the screw being turned clockwise. If this doesn't work, Felix suggests readjusting the TPS, but not by the manual.
He says to cause the idle to hang up by raising engine speed above 2,000 rpm. Do this with the gas pedal to duplicate the actual driving condition. Don't touch the throttle shaft. Hold your engine speed above 2000 rpm for several seconds and release. This should hang the idle up. Go to the TPS and delicately--without any downward pressure--turn the adjusting screw slowly clockwise until the idle speed falls.
You can now shut the engine down and (using the standard procedure) check the TPS. You should get the proper reading. As a double check, with just a little pressure with your finger on the screw with the test light pair hooked up, the second light will light, and go right back off when you let go. Refer to the section on adjusting the TPS for details on the adjustment.
Make sure your tps and V&V solenoids are plugged in. I say properly adjust your TPS by warming up your car, turning it off and moving key into the last position, disconnecting your vent and vacuum solenoids (one plug), THEN adjust you TPS. If that doesn't work then while the car is running have someone press the clutch and turn the TPS screw CW or CCW till the idle falls. Any downward pressure on the screw will change the position of the throttle plates so oh so delicately turn the screw. If all else fails ohm out the tps, should be 1kohm closed to 5kohm open. Best of luck.
12-06-08 | 09:05 PM
#13
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I've glanced over that part of Lane's troubleshooting before, but I couldn't spot anything about why the clutch has effect. I can understand putting an electrical load on the motor would cause variations in idle. Does releasing the clutch put a load on the motor as well (we're talking it neutral, naturally)? Does pushing the clutch in take the load off the motor? That's basically what I'm asking.
I've kind of already figured out that my throttle rod has play, as I've not been able to consistently set the TPS, since very minor pressure on the screw makes it fluctuate, which is why I wasn't asking about the cause of bouncing. I'll try compensating for that some more (I've done that before every so slightly, but maybe not enough), however my above question still stands.
I've kind of already figured out that my throttle rod has play, as I've not been able to consistently set the TPS, since very minor pressure on the screw makes it fluctuate, which is why I wasn't asking about the cause of bouncing. I'll try compensating for that some more (I've done that before every so slightly, but maybe not enough), however my above question still stands.
Last edited by Whisper; 12-06-08 at 09:10 PM.
12-07-08 | 07:50 AM
#14
when the clutch pedal is pressed down or the trans is in neutral, the engine will be at idle speed. your problem is with your idle speed, not being related to your transmission or clutch. a high idle, NOT surging idle, is most commonly caused by a vacuum leak, a gummed up throttle body, a tampered with idle adjust screw, or a problem with the bypass air control valve. as you probable know, the tps does not affect idle speed.
12-07-08 | 02:54 PM
#15
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when the clutch pedal is pressed down or the trans is in neutral, the engine will be at idle speed. your problem is with your idle speed, not being related to your transmission or clutch. a high idle, NOT surging idle, is most commonly caused by a vacuum leak, a gummed up throttle body, a tampered with idle adjust screw, or a problem with the bypass air control valve. as you probable know, the tps does not affect idle speed.
12-07-08 | 05:28 PM
#16
When the clutch is engaged, the clutch fork is pushing the throw out bearing against the fingers on the pressure plate. The clutch disk is unclamped and free to spin between the flywheel and pressure plate. When the clutch is not engaged the pressure plate springs hold the clutch disk against the fly wheel and it and the transmission spin.
Maybe the friction from the throw out bearing pushing against the fingers of the spinning pressure plate is enough of a load to effect your idle.
Maybe the friction from the throw out bearing pushing against the fingers of the spinning pressure plate is enough of a load to effect your idle.
12-08-08 | 05:03 AM
#17
i'm not sure where you are going with this...it explains things pretty well. when the clutch pedal is depressed, your engine will return to idle. there will be no load on the engine. with the pedal released and the trans in gear, you have a load on the engine (and the car wil be moving at that point) and the symptoms will no longer be present because your engine is no longer at idle.
12-08-08 | 07:25 AM
#18
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From: knoxville, tn
This happens alot to my GSL-SE and usual cause of the problem is the dirty throttle body. Clean everything inside and outside very well. y 7 does the same thing, idle bounces (revs) until the clutch gets pushed in then it idles steadily around 2000 rpms.
Clean the throttle body and get back to us.
THis comes straight from the article linked above.
PROBLEM #4: Idle Cycling in Conjunction with Surging (the car speeds up and slows down on the highway even though you are holding steady throttle).
This is associated with a miss-adjusted Throttle Sensor (TPS). Another symptom of a badly adjusted TPS is lurching transitions when trying to gently accelerate and back off--as you might do in a rolling traffic jamb. Since the car is surging with the throttle open part way, you know the problem is not confined to the idle, so adjusting the TPS is a good first step. However, the basic problem can still be dirt in the throttle body or a BAC valve that is not closing. Here is what happens: Your idle starts to cycle, so you take it to a mechanic or friend who immediately adjusts the TPS. The TPS adjustment is designed to match the TPS to the position of the throttles at idle. If the throttles are not closing all the way, the match will be made with the throttle in the wrong position. That, plus compensating with other controls, may tame the idle, but the TPS will be out of position for the rest of its range, which causes the surging and lurching. If you find your car in this condition, clean the Throttle Chamber, re-adjust the TPS and then go through the rest of the Standard Idle Adjustment. That should straighten everything out. If a problem persists, look for the BAC valve to be hanging up and not closing all the way. Clean as in Problem #5.
Clean the throttle body and get back to us.
THis comes straight from the article linked above.
PROBLEM #4: Idle Cycling in Conjunction with Surging (the car speeds up and slows down on the highway even though you are holding steady throttle).
This is associated with a miss-adjusted Throttle Sensor (TPS). Another symptom of a badly adjusted TPS is lurching transitions when trying to gently accelerate and back off--as you might do in a rolling traffic jamb. Since the car is surging with the throttle open part way, you know the problem is not confined to the idle, so adjusting the TPS is a good first step. However, the basic problem can still be dirt in the throttle body or a BAC valve that is not closing. Here is what happens: Your idle starts to cycle, so you take it to a mechanic or friend who immediately adjusts the TPS. The TPS adjustment is designed to match the TPS to the position of the throttles at idle. If the throttles are not closing all the way, the match will be made with the throttle in the wrong position. That, plus compensating with other controls, may tame the idle, but the TPS will be out of position for the rest of its range, which causes the surging and lurching. If you find your car in this condition, clean the Throttle Chamber, re-adjust the TPS and then go through the rest of the Standard Idle Adjustment. That should straighten everything out. If a problem persists, look for the BAC valve to be hanging up and not closing all the way. Clean as in Problem #5.
Last edited by frisbeedog; 12-08-08 at 07:28 AM.
12-08-08 | 11:44 PM
#19
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From: Seattle, WA
When the clutch is engaged, the clutch fork is pushing the throw out bearing against the fingers on the pressure plate. The clutch disk is unclamped and free to spin between the flywheel and pressure plate. When the clutch is not engaged the pressure plate springs hold the clutch disk against the fly wheel and it and the transmission spin.
Maybe the friction from the throw out bearing pushing against the fingers of the spinning pressure plate is enough of a load to effect your idle.
Maybe the friction from the throw out bearing pushing against the fingers of the spinning pressure plate is enough of a load to effect your idle.
12-08-08 | 11:51 PM
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i'm not sure where you are going with this...it explains things pretty well. when the clutch pedal is depressed, your engine will return to idle. there will be no load on the engine. with the pedal released and the trans in gear, you have a load on the engine (and the car wil be moving at that point) and the symptoms will no longer be present because your engine is no longer at idle.
12-09-08 | 08:19 AM
#21
I need to read more carefully (like the title). I was thinking the revs were higher when clutch pedal was out. I also misread the rpm change as 100.
When you push down (engage) the clutch pedal, the clutch plate is unclamped and the engine spins freely, separate from the tranny. You have 2000 rpm.
When the clutch pedal is up (released), the clutch plate is clamped and the engine is connected to the tranny. You have bouncing around 1000 rpm.
Sounds like something in the tranny could be putting greater than normal load on your engine, but I bet not. Car drives and tranny shifts ok with no significant noise?
EFI idle/intake issues can be very puzzling, particularly a worn throttle shaft or a TPS that is intermittent/bad. The tranny should put a little more load on the engine when clutch is out. I'm thinking it is just enough to trigger your bouncy problem. I would check and replace the tps if you think its bad. I assume you've already cleaned and tested the BAC. It's purpose is to compensate for extra load on the engine. The cycling is caused by the valves inside not moving freely. When extra load is put on the engine, the idle goes down. When that happens the BAC gets a signal from the tach through the ecu that the rpms have dropped and raises the idle by allowing in more air. Basically it creates a controlled vacuum leak to raise the idle. Doesn't take much of an uncontrolled vacuum leak to raise the idle 1000 rpms.
When you push down (engage) the clutch pedal, the clutch plate is unclamped and the engine spins freely, separate from the tranny. You have 2000 rpm.
When the clutch pedal is up (released), the clutch plate is clamped and the engine is connected to the tranny. You have bouncing around 1000 rpm.
Sounds like something in the tranny could be putting greater than normal load on your engine, but I bet not. Car drives and tranny shifts ok with no significant noise?
EFI idle/intake issues can be very puzzling, particularly a worn throttle shaft or a TPS that is intermittent/bad. The tranny should put a little more load on the engine when clutch is out. I'm thinking it is just enough to trigger your bouncy problem. I would check and replace the tps if you think its bad. I assume you've already cleaned and tested the BAC. It's purpose is to compensate for extra load on the engine. The cycling is caused by the valves inside not moving freely. When extra load is put on the engine, the idle goes down. When that happens the BAC gets a signal from the tach through the ecu that the rpms have dropped and raises the idle by allowing in more air. Basically it creates a controlled vacuum leak to raise the idle. Doesn't take much of an uncontrolled vacuum leak to raise the idle 1000 rpms.
12-09-08 | 10:50 PM
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Ok. So basically pretty much what I speculated in my original post. Tranny putting enough load to drop the RPM. Interesting enough when my motor doesn't idle-bounce (I can make it settle down if I rev high), clutch does not affect RPM one bit. It's steady and no surging. Only when it's bouncing does the clutch/tranny have effect.
I've taken BAC off and cleaned it and lubed it up. I don't know how much of a culprit it is, probably negligible. This happens even with BAC disconnected. I suspect loose TPS lever on the throttle shaft, which I'm working on right now. Makes TPS read incorrectly. Hopefully I can fix it and see how that goes.
Thanks.
I've taken BAC off and cleaned it and lubed it up. I don't know how much of a culprit it is, probably negligible. This happens even with BAC disconnected. I suspect loose TPS lever on the throttle shaft, which I'm working on right now. Makes TPS read incorrectly. Hopefully I can fix it and see how that goes.
Thanks.
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