Nah kidding...

However, at idle, when warm, the engine surges. Bounces from 1000rpm to about 1200rpm. Acts like a vacuum leak, but I thoroughly searched the engine and couldn't find one.

This just started today. Before the idle was really low...like around the 300rpm mark...so I made some adjustments to get the warm idle closer to 1k. Only adjustment I've made.

Suggestions would be appreciated.

 

Did you adjust your TPS to reflect the changes you made? Still probably a vacuum leak though, almost always is.

 

What "adjustment" did you make to get it to idle back?

 

Sorry...I don't remember the names. Adjusted the set screw on the throttle linkage and adjusted the idle air bypass screw thingy on top of the throttlebody until it was smooth.

Idled fine, 20 miles later....surging.

 

I discovered just now that the surging only happens when the car is in gear.

 

Idle speed drops slightly in gear thanks to the neutral switch, but I don't think that's the problem. I'd say it's a TPS adjustment problem, and the changes in idle speed just make the problem show up easier. I've had the same issues before: bouncy idle at a specific RPM range, but then it goes away once the car full warms & idle drops under 1k RPM.

 

Nah this is only when warm, and only when in gear. Cold she does idle high (AWS), but warm and out of gear she idles between 750 and 1000 rpm...depending on how she's feeling right then...

 

If you put a jumper in the intial set connector, it forces the BAC to stop controlling the idle speed and go to a constant duty cycle. If the surging stops, it would suggest the problem is related to the BAC, or how the ECU is commanding the BAC; if it does not stop it, then the problem is elsewhere.

 

Problem is elsewhere...

Any other suggestions?

 

side question....I thought tapping the gas bypassed the AWS? Doesn't in my car...

 

If blipping the throttle does not cause the AWS to kick down to normal idle, either the AWS is stuck or it is not the AWS which is holding the idle high. If you pinch closed the big tube running to the air bypass solenoid, the idle should drop IF the AWS is the problem. If not, the AWS/air bypass solenoid is not the problem.

 

Placing it in gear bypasses the AWS, not blipping the throttle.

 

I'll try that tomorrow. I have tried starting the car in gear (which is suppose to bypass the AWS) and it didn't affect the cold engine idle at all. I'm still real curious about the surging idle in gear thing, though.

 

Probably need to do the idle adjustment PER FSM. I hate trying to get S5s to idle once the screws have been messed with..

 

Imagine getting a car that'd already been "adjusted". I have no idea what's been tweaked...I played with stuff enough to at least get the idle to settle, but have lacked time beyond that. When I get a couple hours I plan to zero everything out so I can start from scratch.

 

+1 make yourself a ghetto tps sensor adjuster with 2 led's (search its on here) then jump the test connector by your lead coil (2pin geen contor will need a jimper wire) adjust your idle the same way (meaning with the connector jumpped) then adjust your tps. it could be a AFM issue but i would try what i suggested first

 

Odd... blipping the throttle works every time in my car... I haven't tried the putting it in gear thing; maybe that works too.

 

High cold idle...pinched air line to BAC...no change. No effect at all.

Fluctuating idle in gear after warmed up....I checked connections on the sensors on the transmission...all connected.

 

OK, that suggests the BAC is not the source of the high idle. Try the same check on the hose going to the AWS solenoid valve. If the idle drops, it is admitting the additional air.

Another thing to check is the fast idle cam. Check and see that when the engine is warm the roller is completely off the fast idle cam.

 

i have 86 gxl, manual n/a. idle hits around 2300rpm when cold, rev up and down 1500 +/-200 after warmed up. cleaned BAV, unpluged TPS while rough idling(makes no difference), check & adjust voltage of TPS... still didnt work out.
today i had it check with a smoke machine. found out it leaks at the throttle area, where the vacuum pull a smal rod while you start the car. it leaks from a seal/o-ring thingy. i am thinking of changing the whole throttle. i am bad at explaining things, let me know if i made it clear to you.
keep me update with your side please.

 

I have checked vac leaks and it's solid.

 

surging idle is from your tps it either is not adjusted right or you need a new one.

 

I've heard the TPS could cause the surging idle, but it's my understanding that it causes the surging idle at all times. Not just when the car is in gear.

 

I had a problem somewhat similar to this and it ended up being the thermowax. The coolant passages were clogged so it was holding the throttle open a little when warm because it wasn't melting. Which from what i understand caused the cpu to make the timeing advance and cause the idle to surge.

I turned the screw all the way in and it idled fine, just have to give it some gas sometimes when cold to keep it from dieing. Anyone else think that might be the OP's problem?

 

As far as I can tell the thermowax may very well be an issue...but it's a matter of initial adjustment and I need to go out and reset everything. It does appear to be working properly because it idles just fine after it's warm. I'm pretty sure it's a TPS/thermowax/idle set adjustment issue as far as the high idle when cold.

To my knowledge the AWS isn't functioning at all.

Today I went over all my tranny grounds again and everything is making good contact (checked continuity through all grounds). That was my last idea as far as the surging warm idle in gear.