kleach18

How would I go about ajusting the idle on my 90 GTU? IS the TPS screw the only way I can do this? Help please!!!

gold87na

You dont adjust it by the TPS.. If n/a it's under a black rubber sock directly on top of your throttle body. If Turbo2 i believe its on the BAC on the drivers side of the dynamic chamber..

kleach18

ok thanks

kleach18

ok thanks is that on a 89+ or 86-88?

Mazdarules

Download the service manual that is posted online (at fc3s.org I think?). It will show you how to do all the regular maint **** and other stuff too. There is on specifically for 89+ fc's.

If you are a newb, it's better to see the pictures in the manual's than to have someone try to describe it to you.

kleach18

My computer is F***ed up so please just try to explain it. I tried to download it and stuff for like a hour and couldn't get it to work. Need to reformat my hard drive but don't have time.

asherwood

I tried this method on my '91 N/A and now it's running the *****! I wouldn't recommend playing with the air bypass screw to adjust the idle.

A lot of the posts to the forum are talking about the setups on the pre '89 cars and don't apply! Each time that I have asked specifically about the '91 the place goes silent.

I cleaned the TB and the idle went all the way up to 2500rpm and stayed there, I tried adjusting it down with the screw located on top of the TB all it did was richen up the mixture by changing the air ratio and my milage went into the ditch! I was getting nearly 500km to a tank (still not very good) and after playing with the air bypass screw to reduce the idle that dropped to only 280km! (280km = 175 miles)

If you ever figure out the correct way to adjust the idle on a FC that has dual TPS sensors (coarse and fine) and maintain the proper air bypass mix let me know!

live4boost

iTrader: (2)

I would recommend going to your local parts store and picking up a Haynes manual. Make sure that it is the haynes. There are very specific and have lots of pictures. It is the most useful thing that I have bought for either of my TIIs.

91vert

There is a whole procedure to follow on getting the car to idle correctly.

You need to first adjust the TPS using a check light that you can make. Do a search for this and somebody has probably posted a link to where you can get the instructions on making the light and the proper procedure to follow to get it adjusted. I don't know what it is or I would post it. Even with the check light, these TPS's are a bitch to get just right. After adjusting mine with the light, I had to go out and drive it around, come home and do it all over again making slight adjustments each time until I got it right. There is absolutely NO allowance for being sloppy with this procedure. Once you have it adjusted, LEAVE IT ALONE!! If the TPS is out of whack, the Air Control Valve will not function correctly and screw the idle up bad.

Once that TPS is adjusted you need to jumper the single green connector up in front of the drivers side shock tower to ground. This bypasses the BAC valve and any ECU adjustments to the idle. With this jumpered, start your engine and your idle should be close to 750 (engine has to be at operating temp too). Adjust the idle with the screw on top of the throttle body to get it as close as possible.

Once that is set, make sure you check the ignition timing. If that is off, it will make the car idle higher or lower.

Once that is all adjusted, shut the engine off, remove the jumper wire, and then restart. It should idle fine.

Of course there are a bunch of other things that can screw up the idle. The BAC valve might be stuck open, you could have a vacuum leak somewhere (check all vacuum hoses), other sensors malfuntioning, etc.

Is your check engine light coming on? Are there any other problems with the car? Any mods?

asherwood

The problem with my setup used to be: When I turned on the headlights, applied the brakes, etc. the idle would drop down real low (~400-500rpm). When there was no load the idle was solid at 750rpm so I assumed that the TPS was adjusted correctly, just the ECU/BAC's response to increased engine load was out of spec.

So, I cleaned the TB 'cause it was pretty dirty, that's when the idle increased. I never adjusted or changed the TPS settings. I removed the BAC and cleaned it out, checked the operation and all is good there. I checked all of the hoses and can't seem to find a vacuum leak either. I checked the timming when the idle was at 750RPM and it was right on the factory spec. Checked the O2 sensor, it's voltage measures good as well.

There are no engine mods of any kind, the check engine light is not on either. But the idle remains stuck at about 1700 rpm and when I tried using the air bypass screw to reduce the rpm that's when I could smell the rich exhaust and the milage went into the tank! No other problems that I know of regarding the engine.

I'll take a look in the FSM for info about the TPS check light and search these forums, however as I mentioned before most (if not all) of the information I find relates to pre '89 cars that as far as I know have only 1 TPS sensor where as my '91 has 2 (coarse and fine)

I'm of course open to suggestions and ideas on how to proceed. Thanks

HAILERS

Adjust the throttle plates per the fsm and make sure the idle stop screw isn't the culprit keeping the idle high.

avrfan

For high idle check your throttle cable slack and also check the cruise control cable slack. On my car, I had the cruise control cable too tight.( You mention you took the throttle body off to clean it right? )

QUESTION: Ok, sounds like some of you guys have adjusted your TPS before right? I believe you do this with the ignition key on but car not running right? Ok, I did the TPS adjustment using the home made 2 LED tester. When I was adjusting the TPS screw to get one LED on and the other LED off, I would hear the BAC valve start buzzing when I adjusted it to both LEDs off. It sounded rough like a dull clicking sound. I thought it sounded like a bad BAC but the car idles fine so anyone else know what their BAC sonds like when doing this adjustment?