Introduction and Idle Problem (Long Post)

Ok if you disconnect the IAC and the engine dies the MIN idle is not set correctly. Normally the ECT will set a code the idle speed also depends on the ECT readings. I think the number is around 140* If the sensor is marginal it may be your issue. But not likely. Well replace it with the one from your donor car that runs correctly. Anything is possible. Are you Sure the TPS and MIN IDLE IS SET CORRECTLY?????????? Feel the return hose under the lower to see if the coolant is HOT. If its not the lower or the feed hose is blocked. Also the wrong intake gasket can block the coolant flow through the LOWER. But this should set a code. Keep on digging in and good luck

I set the TPS with the IAC disconnected to .94 volts at ~700 RPM at operating temperature, so it should be set correctly. I also checked it two weeks later and the setting was still correct. I was amazed after I did that the car actually did high idle when cold and once it began to warm up it dropped to 1000 RPM like it should. It never did that before! I will change the ECT with a know good one and make sure the passages are clear to see if it helps.

Thanks for everyone's help and keep the ideas coming!

i know that throttle body gasket isnt much, but it could be a vacuum leak you cant hear. thats how mine was, just light enough to make a difference.

96 700 RPM is low. Set it to at least 800. This will probably not make any difference but what the HECK. The TPS at .95 IS GOOD. Now make sure the ECT is good and the watter passage is FLOWING PROPERLY. Code 42 rich mixture. Is the O2 GOOD???? Just picking at straws???? Is 42 Intermittent??? The O2 may play into this situation depending on its cross counts. Check the O2 Heater circuit and the O2 heater resistance. The heater may be open???? Once again picking at straws. Without seeing the car troubles like this are TUFF. Good luck

Check the voltage at the O2 heater??? Then check the O2 heater resistor with an OHM METER. Hay you never know. The O2 may be cooling off and the ECM will go OPEN LOOP. Then check the O2 output voltage at 1500 RPM'S Does it TOGGLR rich lean??? Just a thought??

Originally posted by 84TBirdTurbo42:
i know that throttle body gasket isnt much, but it could be a vacuum leak you cant hear. thats how mine was, just light enough to make a difference.

This is where the smoke test comes in handy. Personally i have never seen a gasket go but that does not mean anything. Anything is possible. Erattic idle is a PAIN IN THE TAIL to say the least. Personally thats why i like the 5.0 IAC it controlls the idle much more precise. I know the stock setup should work as designed. But things Happen. Clearly the ECM is seeing something that triggers a higher RPM. What about your alternator. Is it relitively NEW. Sometimes a noizy alternator can play HAVOC on the ECM and mess it up with excessive NOIZE.Do you have a good PCV VALVE??? They can cause this problem if not seating properly. Its a stretch but it can happen. Something is increasing your idle and the culprit is inducing air(VACUUM LEAK PER SAY) I once had a GM car that had a MISS. When i removed the battery lead from the alternator the MISS DISAPPEARED. Figure that one out. (I DID) Good luck

The 42 code is intermittent. I found out years ago if the check engine light comes on, the only thing you have to do to make it go out is run it through the gears and it will go away. Around 5 grand in both first and second will make it go away every time! I am on my third O2 sensor. This one I bought from Ford and they used the calibration code on the door pillar to order the part. It only has about 3000 miles on it and the code 42 will still appear at random. It usually takes about 3 months for the code to reappear after the Italian tuneup. After I found this site and discovered it was probably the VAM and not the O2 sensor. Oh well, at least I have a lot of spares.

I have replaced the PVC before with no effect. The alternator is original. I had it rebuilt about 100,000 miles ago with new brushes and bearings. A local shop rebuilt it and I don't know if he checked the electronics. It does charge correctly. I was planning to upgrade it soon.

I also forgot that sometimes the idle will increase after the famous 2.3 turbo hiccup in idle. With every hiccup the idle will sometimes increase about 100 RPM. Once again this is totally random.

HI Paulie! BOth times, my ECT was changed, and cleared up the idle issue, it did not set a code.. Strange, but I ran the test more than once, never got a thing. Then started with items that did not appear in the code book, the ECT is not in my code book, changed it first, and the screwy Idle (looping) went away.

Now make sure the ECT is good and the watter passage is FLOWING PROPERLY. Code 42 rich mixture.

I know thats why i posted this. The ECT controlls the mixture and the IAC position. Thats why i posted this. Martin the ECT is one of the most important sensors. Thank You

I had an idle problem similar. Mine though didn't trigger the CEL. I replaced the Fuel Pressure Regulator and my idle dropped to normal and has stayed that way for awhile.

Is the orange O2 ground wire connected to the turbo inlet bolt?