Have a 94 firebird LT1 engine changed igintion module (MSD) coil (MSD) idle air controller, rebuild computer, after all this engine doesn't idle properly. After engine starts it idle as it should until the engine warms up then it begins to surge to 1500 and 2k rpms. Dosen't throw any codes.....any ideas?????

 

What does it do with the MAF disconnected?
Do you have access to another computer?
Are the vacuum ports in the Thrortle Body clean?

 

Sounds like the problem is when the car goes into closed loop. I would check your o2's or have them replaced.

 

no don't have another computer, I will check ports as you suggest

 

will check them out, keep ideas coming guys

 

in my earlier post regarding the idling problem I'm having with my 94 firebird (LT1 engine) I got a couple responses, I've done what was suggested and still no joy. Would it be cost effective to go back to a carburetor fuel system. just wondering...........

 

If your throttle position sensor is out of adjustment it will cause a high idle condition. Get yourself a Haynes manual or research this site for the proper voltage readings. I think WOT is supposed to be 4.5 and idle is .7v. Not positive on that.

 

Thanks will check it out.........

 

Can you data log the car from a cold start to when it starts acting up?

Can you list out all the car's mods?

 

^^^, yes TPS VDC wants to be .67+/- blades closed and 4.5 blades full open. The volts should increase smoothly as you open the throttle blades to full

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if you have a larger aftermarket TB the stop screw may have been F with to deal with low idle issues. That can take VDC off for the TPS. Can cause other issues also on A4 cars

Your issue could be something else but TPS is a possibility so just check with a DVM.

 

I have had customers with Holley 58mm TBs, that had the TPS mounted where the TPS showed close to one volt at idle. Screw holes mis-drilled, or pin in the end of the shaft not "clocked" correctly. I had to slot the TPS screw holes so I could adjust the voltage at idle. Under .8 volts work well at idle, 4.5V @ WOT. Over 4.5 @ WOT doesn't bother anything I have seen.

 

Check the wiring going to the O2 sensors also. I had a couple of wires get up against the header and melt together. Would not idle right when it went into closed loop. About drove my repair shop crazy. Wiring would still show continuity when testing!