First a little information. I just installed a new throttle body (58mm) in which I transferred over the old sensors (which were working fine) along with SLP runners. After that I put in a new torque converter. And then I put a new true dual exhaust on the car including new headers.

Now the problem: I start the car, it revs to 2k and idles down to 1k. When I let off the brake the car will accelerate, and if I give it even the slightest amount of gas it will start to pick up speed and it wont slow down. Its like trying to reign in a runaway horse. I have to keep a foot on the brake just to keep the car in check. And when I go to stop the car I have to press the brake almost all the way.

It seems like a vacuum leak to me, but what I don't understand is why would it idle down to almost where it belongs. Anyone think it ISNT a vacuum leak? If so, what in your experience could it be?

 

You didn't say, but did you go through the procedure to re-adjust your minimum air rate? then re-adjust your TPS ?

 

agree, what he said. You probably need to adjust your TPS, its probably incorrectly set, showing too much voltage( i.e. open throttle)

 

Does the 91 not have an automatically adjusting TPS? I always thought it did.

 

it should NOT if its a 5.0/5.7 tpi

 

Here's how you set the min idle.....

unplug the IAC and put tape over the holes that feed it, both on top and bottom of the front of the throttle body.

Adjust your minimum idle with the screw with the tape over the holes and IAC disconnected

Once you get the idle where you want it, take off the tape, and plug in the IAC

Done.

however, you will not see a drip more performance from that throttle body, so all this work is for nothing.

GOOD LUCK!

 

Here is how I ajust mine
Idle Air Control
Tools needed:

Torx bit # T-20
Paper Clip
Small Punch

Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.

Turn on the ignition, but don't start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "IDLE SPEED". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).

If you set an SES light by having the IAC disconnected, then after shutting down the engine disconnect the negative battery terminal. Wait 5 minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.

 

My car was doing that. Look at the carpet around your gas pedal. There is some rubber padding/insulation under it that sometimes can prevent the gas pedal from releasing. No kidding.

 

UPDATE:

Went and tried to adjust the IAC, had zero effect. I had the throttle blades closed off 100% and this dang things still idles at 1500+ RPM. I'm going to take the IAC off and check to see if its stuck all the way open or something. I mean its got to be air getting in somehow right?

Ideas?

 

Your on the right track checking out your IAC, Also you said you installed SLP runners, are you sure all the gaskets are sealed and gaskets are on correctly? Any broken vacuum lines? You can check for vacuum leaks with a 1/4" hose in your ear and or carb cleaner being sprayed around gasket area's. Just curious as to why you added a 58mm TB?

 

you know what,sometimes a bad or clogged egr can cause high idle. unplug it and start it up.