I rebuilt and painted my 1989 v6 2.8 MPFI Firebird over this past year, rebuilt engine, trans, and replaced tons of other parts. The engine and trans have currently been in the car for a little over 1000 miles. I bought this car for 500 bucks from a chick that had taken very good care of the interior but had some how blew a head gasket and bent 6 push rods to the point that the car would not even cough. Anyhow rather then rebuild the engine myself I was really lucky and found a factory remanufactured engine heads and all for 400 dollars. While installing the engine I had put a set of 3.1 injectors in to replace the original ones. Once I got the engine in and running I noticed the 2k idle. I had heard that with the 3.1 injectors that higher idles were common so I did not put much thought into it because once I put it in drive or reverse it would drop to about 1000 which was much closer to what I thought was normal.

Fast forward 1000 miles and here I am replacing the 2.8 injectors because of gas prices. GRR... I was curious if I could get better MPG and get rid of the 2k idle because it’s really annoying when you can’t leave the car idle very long because of heat. Replaced the 2.8 injectors and to my surprise the 2k idle was still there!! It was the same issue where when in drive it is fine. I was then on a crusade to find the cause of this high idle. I cleaned the AIC and noticed that there was a lot of black soot. Taking the TB off I noticed the whole intake was covered with the same soot. I am assuming that this is a product of the 3.1 injectors. Checking the TPS I got 0.47 volts lower then the 0.53-0.57 that it should be. Re-adjusted the TPS to 0.55 and still nothing. When i had the TB I noticed that the cap was off of the Idle setscrew. I adjusted the screw so that it just barely touched. Still nothing. I had replaced the ECU because the original was fried. im telling you this girl did a number on this car or her BF did when he was trying to figure out what was wrong lol. In any case I tried changing proms, I noticed a slight difference and I think I like this one better. However still no change in the high idle problem if anything it’s higher.

I hope I have not put any of you to sleep with this background information.

SO THE QUESTION
I am looking for other reasons for this high idle. I have no codes and I am pretty much lost. Another thing that I think is important to know is that this high idle is there when it is cold and stays even when it gets warm. When cold it’s a little lower 1800, which is still too high in my book. I think it might the coolant temp sensors but I replaced all of them if I remember right. Any ideas or advice will be greatly appreciated.


As a side note this website is honestly the best source that I have found for thirdgens. I can not tell you how many times I have found my exact problem on an old thread and the answer. I was miffed that I couldn’t find this one however that’s why you guys are here. Thanks in advance.

 

I run 3.1 injectors in my 2.8 and it idles where it should. That black soot is from the EGR which sends some exhaust back into the motor for emmissions but you really don't need it. Look up how to reset your idle and really clean out your TB. Other than that it could only be a vacuum leak.

 

Does anyone have a place where there is a guide for resetting the idle?

I looked over all of my vacuum lines and cleaned my TB out but still no change. Having the idle jump up 1000 rpm because of a vacuum leak? shouldn't I hear a hissing noise?

 

Alright I just got out my code checker and checked for codes... I got a code 12 and thats it. so that is just saying that the test system is working is working. No info there. Turned the car on and mind you this car is hot. and it is flashing open loop. putting it in drive and it still was in open loop. I decided to drive it around a little to see if it would go into closed loop. No luck the car stayed in open loop the whole time. Now reading the trusty book that came with the code readerI found that there can be 2 reasons for the computer to stay in open loop.

1. The oxygen sensor is not hot enough to operate. (not the case the car is reading between 110-220 all of the time.)
Or.
2 Open circuit problems exist (bad sensor or wiring). Note that this condition will generate a trouble code.

I have had no codes for the whole time that I have had the car. I am going to look at the oxygen sensor when the thing cools down. Those little v6's get hot very fast.
Does anyone have an idea as to why the ECM keeps the car in open loop? I will drive the car tomorrow to work with the A and B terminals jumped so that i can see if the car ever gets out of open loop. at this point im not really worried about hurting the car since it has run like this for a 1000 miles just fine. I do need to get it into a closed loop so my gas mileage will go up.

 

I noticed if I have any rich conditions on my car ..the O2 doesnt last long.The first time I blew one, was installing 3.4 injectors in my stock 3.1.All cars seem to do different things when the O2 is dead.Mine wouldnt run at all...swapped out to a 92 ECM and just did some major repairs and blew another one,car runs in open loop but rough and if I drive it forget it.My TBI truck is easy on them..only replace them due to mileage/age.I would try a new one and recheck it to make sure it goes into closed loop.Another thing is these ECM's systems arent very sensitive to sensor failures..it will take a long time to turn on the SES light or not at all.ANd me too have not had any codes in the time I owned this car ..except a IAC motor that lost its tip..It failed completely and the light came on.I have never had a rich code at all..

 

Update:

I was poking around and found a cut in the insulation on the wire to the O2 sensor. I replaced the sensor thinking I had found the problem or part of it. Started the car and the idle was exactly the same =(. I drove it around with the code reader plugged in so I could see if it would go into closed loop. and it did right away! But I still have the high idle any time its in nuetral or park.

I cleaned out the TB gallorys again and replaced the IAC valve. Still no change.

I switched proms once again and still no change. The second (original) has a slightly lower idle.

I am really lost because the car runs great. I have driven the car like this for 1000 miles. I really want to get rid of this high idle.

 

you ever get this fixed?

my firebird does the same high idle, but it goes on and off, anyone know what could be wrong?

 

Yes I did get my car fixed. It turned out that when I put the vacuum system back together I switched the pcv valve and manifold lines causing a controlled vacuum leak that made my car always idle high.

 

how did you adjust the TPS? Also how do you test it? I'd like to check mine. I tend to idle a bit low. Thanks

 

Well here is a thread that has instructions

https://www.thirdgen.org/forums/tech...t-working.html

Same one I used look at the third post