jkrueger

iTrader: (2)

Orignal post:
"I've been working on this for awhile and can't figure it out. Here are the symptoms:

Once the car warms up the idle varies or surges between 1200 and 1500 rpm. Cold, it won't idle at all, but that I can live with it. It doesn't take more than 2 minutes before it will stay running and starts the surging idle. Normal driving and hard driving the car performs great. No hesitations, boost comes right up and stays up. Power all the way to redline.

Here is what I have checked:

Pressure tested the TID, intercoller and the rubber 90's: no leaks. Sprayed carb cleaner all over the engine looking for vacum leaks: none found. Created some of my own vacum leaks to see if it made it worse: no affect. Replaced all the vacum hoses when we rebuilt the engine 1800 miles ago. Adjusted and tested the TPS from one extreme to the other with no affect. Tested the BAC valve: tested ok. Disconnected the BAC valve: no affect. Cleaned the fuel injectors: no change. Tested fuel pressure at the pump and at the rail: within specs. Iginition is set as close to specs as I can get with the idle the way it is. Checked the positon of the CAS at TDC to my other TII ( that runs fine) and they are the same.

Here are the mods:
K&N filter
S5 turbo and manifold
S5 throttle body
street port
RB 3" turbo back exhaust
ACT clutch and pressure plate

I'm all out of ideas........................."

Solution:

So the final fix ended up adjusting the primary throttle plate. It was open just a little too far, making the engine run lean. So the ECU would compensate by adding a little fuel which would idle it back up some and then it would go lean again. Hence the surging. So I just adjusted the primary plate farther closed and that fixed the problem. Idles real nice at 1200 rpm now. Thanks for the input from the guys who gave it.

JC

truespin88

Wow. Congrats on getting it fixed.

86GXL

How did you adjust the primary throttle plate? Like where on the car N stuff... i'd like to try this

13bpower

good info, I need to get my car to idle above 500rpms. Maybe I could fiddle with that and bring it up. BAC, blah, blah, blah... I want to take that thing off because it does nothing as it is. $450 for a new one isn't about to happen.

jkrueger

iTrader: (2)

86GXL:
Here is a link to Factory shop manual.

http://www.teamfc3s.org/main/factory...ual/1986_1988/

page 4b-62 and 63 (for the 86-88 turbo model)

The adjustment instructions are in section 4a and 4b (na or Turbo) under the subsection of "Intake air system". The 2 screws are on the back of the throttle body. The lower one adjusts the primary plate position (has well as adjust the fast idle setting), and the top adjusts the entire linkage (both primary and secondary plates. The top one is like steppng on the gas pedal, just in really small increments. To adjust the front secondary plate go to the front of of the throttle body (closest to radiator) and there is a small bolt on the end of a rod that is attached to a linkage that goes to one of the pots (near the TPS). I tightened this down a little to close up the front secondary.

The best way to make all these adjustments is to take the throttle body off, which is a major pain in the butt. But you can see what you are doing a lot better. Other wise using a small mirror to look at the back of the throttle body and inside at the plates would work as well.

jkrueger

iTrader: (2)

13bpower:
Try adjusting the top screw on the back of the throttle body. This will open up your throttle plates a bit and raise the idle. I did that to bring mine from 1000rpm to 1500rpm. It like to idle higher due to the street port.

JC