Possible ECM problem Need help :(

Hey guys, I have been reading these forums for a while. And since you are all real smart with luminas :) i thought i would ask you this.

Forgot to add what she is. 1991 Lumina Euro 4door. 3.1L engine 4speed Auto trans. (stock red paint still in good cond :) )

My car used to run fine, Shes 14 years old. Has 140X97X or so and all of a sudden she started acting kind of odd. At stop lights and anywhere where i have to make a stop, she likes to drop down on the rpms, and fluxuate. and she then acts like shes about to die, and sometimes does. I can put her on the freeway or down the street and floor it and she is perfectly fine. She runs like the champ she is and always has been. Nice lil V6 she is.
Also she tends to sometimes start up not as good as before. i dont get her doing the 2k rpms and drop down to 900. like she used to.

So i took it to my grandfather, he first looked at it and all. change one of my battery bolts since it was corroded nastily, so got that done and all. He put my altenator on the meter. and it was doing a nice 14.2 Which is in the good range of 13.8 - 14.2 So no problems there, Battery measured 13.x volts i forget exaclty. but it was all fine for voltage reason. Then he proceeded to clean my engine since it was dirty :) (simple green and hot water heh) so now my car looked even better than before. So he sent me packing, i went down the street stopped at the sign, bam she did it. startted fluttering and died. just like before. i put her in "N" Foot on the brake, Started her. Starts right back up. and then i proceeded home.

What i have been doing is treating her like shes a stick, Left foot on brake. Throwing into "N" giving her just a tiny bit of gas at a stop or light, and when time to go foot off brake off gas then throw into drive press gas. heh it works. When the car is cold she runs fine, When se warms up is when i have a problem. My grandfather said he thinks its the ECM. and on my dads old Bronco II (hate that thing) he had the same problem. We also had the same mechanic at the Local ROP school check it on the scanner (hes a family friend mostly) and On my car there were no error codes. Just like my fathers bronco II. The only thing he saw wrong was the o2 sensor was reading a little weird. and the Temp gauge wasnt matching the ECM's engine temp. The ecm told him temp was around 204 and the gauge read around 140 - 160 The gauge is just a little slow. And the car is running rich instead of lean. Which is a nice thing. He said he thinks that something mechanically wrong is making the o2 sensor be weird. But i think the ECM is reading things wrong and acting up. The o2 Sensor is less than 4 months old. Im sure its not that. no one has done a thing to it let alone touched it since that time.

If anyone has ideas. commentary plz let me know thanks.

Sorry for typos or anything, im just really tired. this car is making me crazy right now. and keeping me from work.

Could be alot of things but a very common one on may GM cars is the TCC solenid. Don't always show up on codes either. The usual symptoms are a strange sensation of an old car stuck in high gear (standard shift) when you try to slow down. Usually stalls out, starts quick in neutral or park, then stalls again when you put in gear. When it cools down works OK, but acts up when warm. While there could be other factors such as Idle air control carbon build, or clooged injectors etc causing this you can check the TCC easy if yours is a 3 speed. Unhook the 4 pin connector from the transmission and run it a while and see what happens. If this is the culprit can cost 150-250 to fix (very labor intensive). If not, move on to common items such as IAC, filters(fuel and air), the rubber plenum going into your intake(can crack and suck air) as well as ALL of your vacuum lines. I am sure you will get additional feedback on this as well.

Its a 4speed. And she shifts fine, and doesnt feel like shes in a diffrent gear than what i know she is in. Never stalls when i put her in gear. I can start the car. and leave her in park when warm and she doesnt do anything odd. Untill i move her a little bit. If i put her in gear and move her a bit and then hold the brake and watch the rpm you will see it. its odd i dont understand her lol.

Might be the IAC, those won't last forever. The TCC sounds more like if you hold it steady and it kinda lurches, or if you start braking and it acts like a manual left in gear without clutching at a stoplight.

The IAC is pretty easy to swap, but isn't that cheap.

When i start slowing down and encounter the problem she does lurch. Its as if she were put into nutreul and then reved a little bit, and then switched back to drive. She does that then proceeds to die. Is this what you guys think it is? or something of this sort. I have work tomorrow and if i can get this thing fixed tonight then i will be happy.

Also any insight on where it is located. How much. Alternatives. i have read the other posts but just want to get the most commentary i can to Fully understand all of it.

Generally it is under the air filter assy, on driver side of vehicle. remove the intake hose, filter cover and then the bottom part of the filter holder (I think it has a single bolt). Should be able to see the 4 pin connector then. One thing I noticed though, is that you said it was a 4-speed. I read in another post last week that the 4 speeds should not be or could not be unhooked the way a regular 3 speed is. Every one of these I have encountered has been on 3 speeds. Anyone out there who has dealt with these?? (The TCC itself is in the transmission, need a transmission shop to replace if bad). On cars such as my Corsica (91) if you unhook the 4 pin connector it goes just fine as is, but loses some gas milage. For the record, mine has been unhooked for over a year.
The IAC sits in the front of the motor, has 2 screws and a wire plug. Might try taking this out and cleaning it. they carbon up a lot.

Go for the IAC or the MAP. I know the later 4 speed autos start getting integrated in the plug designs; my 1991 had a seperate connector for the TCC and some other thing, and my 99 has just one fat connector that does the whole shebang.

If it is the TCC and you want it fixed...god help you pay the bill or do it yourself. Its VERY involved.

You stated that you had your car hooked up to a scanner, and it said it was running rich? Not good. The car should switch back and fourth from lean to rich, almost 2 to a second. The O2 sensor is what controlls this. I think you may have a problem with the O2 sensor again. Otherwise, like they said, IAC, and check for vacuum leaks. Good luck

It did switch back from lean to rich. But from what im told its supposed to be 10 times every 10 seconds. it wasnt doing 10 a sec. But still something is going on here. im wondering if i should take it to a shop have them replace the TCC or not...?

Hi i am new to this forum but have been a GM Tech for 20 years.
On a lot of late 80 to mid 90 GM vehicle you have to relearn the idle if battery is disconnected or ECM replaced. First disconnect the battery for 2 minutes. Then start engine with all accesories turned off, and let idle in drive for 10 minutes (no cheating make sure it is a minimum of 10 minutes). Turn off vehicle for 1 minute. Restart and let idle in Drive for 5 minutes. if the RPM's fluctuate while idling you can slightly increase throttle to compensate but try not to use any throttle input. Hope this helps. we get a lot of this idle surge complaint after the owners changed the battery. It sound stupid but it works. Also you CANNOT diconnect a torque converter on any overdrive transmission it will overheat the converter and cause major internal damage to your transmission

Hi i am new to this forum but have been a GM Tech for 20 years.
Also you CANNOT diconnect a torque converter on any overdrive transmission it will overheat the converter and cause major internal damage to your transmission

Welcome to this board, and thanks for your input. I didn't know this about the OD transxls, what if one were to leave it in the drive position with the TCC disabled, as a "limp along" solution until repair could be made?

Would that be OK, or no?

Thanks again!:iceslolan

Hi i am new to this forum but have been a GM Tech for 20 years.
On a lot of late 80 to mid 90 GM vehicle you have to relearn the idle if battery is disconnected or ECM replaced. First disconnect the battery for 2 minutes. Then start engine with all accesories turned off, and let idle in drive for 10 minutes (no cheating make sure it is a minimum of 10 minutes). Turn off vehicle for 1 minute. Restart and let idle in Drive for 5 minutes. if the RPM's fluctuate while idling you can slightly increase throttle to compensate but try not to use any throttle input. Hope this helps. we get a lot of this idle surge complaint after the owners changed the battery. It sound stupid but it works. Also you CANNOT diconnect a torque converter on any overdrive transmission it will overheat the converter and cause major internal damage to your transmission


Dude i honestly love you. Heh. Thanks much for all your feedback guys. I really appreciate it. and my car is actually a 3speed with a Overdrive, which i just found out earlier today. But i would like to say thanks. It was a matter of relearning the ECM. and nothing more. The car Runs like the champ she is. A lot quieter on idling now but i can fix that. Some flow masters. and a cold air intake could do it :)

Thank you all for the help i appreciate it