Thread: Stalling issue 90 3.1 SE

First, my car is a 1990 Pontiac Grand Prix LE with a 3.1 MPFI V6 paired with the 4T60 Auto trans. The problem I am experiencing started out of the blue, for no obvious reason. When I turned the key, it would turn over and start for about 1-2 seconds, then die. If I give it just a little bit of gas, it would start just fine but soon as I let off the gas, it died. Had to drive it 20 miles home using both feet, lol. I thought it might have been the fuel filter, changed it and no fix. Thought maybe the Throttle position Sensor, replaced it and it helped a little, but did not fix it. Replaced the Idle Air Control valve, that helped with the incredably rough idle, but did not fix the problem. Since then, if I start it while giving it a little gas, then keep the RPMs at around 1,500 for 2-3 minutes it will idle on its own. But if I keep the idle too high (2,000 -2,500) the SES light comes on, but will turn off when I let the rpms go down under 1,500. Pretty sure that is just telling me the RPMs are too high. Occasionally the car will begin to climb in idle speed up to 2,600 +/- all on its own, for a while, then go back down to 1,100 +/- . This causes the SES light to come on as well. Other than that, the SES light DOES NOT come on.

I thought it might have been the ECM so I beat on the ECM and wiggled it around real good, which sometimes kills the car while idling, if the ECM is bad. It kept running. I also discovered that my ECM is not very old, and a re-manufactured Delphi ECM. Thought about the EGR as well but it is digital so I cant test the EGR valve without a diag. machine... I checked the Manifold Air Pressure sensor and the connector is broken. I was told that to test it, have the car running and un plug it, and if the car keeps running, its bad. And when I did this, it kept running. I also remembered that after giving the car a tune up, I took it down the freeway really fast, then slowed down to try out the cruise control and it didnt work. I pulled over and discovered that the vac hose to the map sensor was not plugged it. Cruise control worked after plugging it back in. After consulting my Dad (35 year mechanic) and he things it is probably the MAP sensor. But I figured I would ask you all about this as well. I dont want to spend the $60 in replacement parts just to have the problem remain. I apologise for the book, but I wanted to be descriptive to insure accurate answers

Anyone have any input for me?

Replaced the IAC valve and Throttle position sensor, and cleaned the throttle body with a rag.

Ok so, I replaced the map sensor and map sensor connector and the problem remained. I took it down and had a diagnostic test done and it says that the map sensor was malfunctioning, but then showed function(possably an old code) and the EGR valve was not functioning at all, even at 2,000 +/- RPMs, and the IAC valve... You know, the one I just replaced with a brand new part from Kragen, is not recognized... According to the ECM, the IAC valve isnt even there. So I am gonna try and "re-install" the IAC valve and take the EGR valve off and clean off all the carbon deposites and crap out of there and maybe that will take care of it... Hopefully... Any other ideas though?

I posted befor about my issues with my 1990 GP LE, stalling. Well it still does it. It will not cold start without giving it gas. It only turns over, sputters and dies. When it is hot, it will occasionally start without giving it gas but not always. I have changed the IAC Valve, Throttle Position Sensor, MAP Sensor and connector, EGR Valve and hose, All vacuum hoses, reconected this thing under the drivers side front end that had a vac hose running to the other vac hoses but was broken, dunno what it is but I re connected it, any ideas? I gave it a complete tune up, with an oil change at a lube shop 2 days befor the problems started. Cleaned the intake of all carbon deposits and other common nasty crap. Had a diag. done on it which showed the EGR was not functioning, which is why I replaced it. The new IAC valve was not functioning at first but started to function halfway through the test. I figured it was just reading a previous code when it read malfunctioning. I am going to take it down and have a diag done again tomorrow as well. I am tired of replacing parts and spending all this money on it just for the problem to continue. It seems that with every part I replace it gets a little better, but still... Enough is enough. Can anyone help me solve this infuriating issue? Thanks.

Thank You BillBoost37.

Any thoughts/suggestions anyone? Headed down to get a diag. now.

Diagnostics read that the car has no problems at all, everything is functioning as it should. But it still runs like crap, wth is going on? The mechanic was baffled, told me that everything he could think of that would cause these problems, I have replaced.

Bump... Can anyone help me out?

I just cut off the catalytic converter hoping that it was plugged up, not allowing the engine to "exhale". Unfortunately that wasnt the problem either.

Someone has to have some idea on what the problem is! Any help is appreciated!

Ok so... I thought I had this thing fixed, but I was wrong. I had replaced the Coolant Temp sensor and connector, re set the ecm, replaced the IAC valve and gasket and intake gasket. The car ran PERFECTLY, All day. The next morning I went to start it up and it was running like crap again. Took it all apart and reset the pintle of the IAC valve, which imo was too far open, made sure everything was connected properly and clean. Then re connected the battery and it ran PERFECTLY, AGAIN. I went out to start it up this morning and it is running like crap AGAIN. When I disconnect the battery and reset the ECM, and disconnect the sensors and re connect them, then start it up, it runs great all day. Idles at 1000 rpm, great acceleration, no hesitations or anything, couldnt be better. Then the next morning it idles at 2000-2500 rpms and sounds/runs like crap. It is like the ecm is not retaining the information that I replaced the sensors and and reconnect everything over night and it is reverting back to bad information, or what have you. What is the deal? Is my ECM failing? Can anyone help me out? I am about ready to unload every bit of ammo I have into this stupid car

Well, I got it mickey moused fixed... Sorta... I found that the IAC valve was opening on cold starts just fine, and closing when I turn the car off, as it should. But it always opens, and does not close when it is supposed to, regardless of engine temperature. The way I got it "fixed" and running was to un-plug the IAC valve that is installed and plugged the connector in to an un-installed IAC valve, with a removed pintle. So the car thinks the IAC valve is functioning or whatever, but it is really not. Basicly it is on permanant choke I guess. Just have to give it gas on cold start to open the butterfly to allow air in, kind of play with it for a minute or 2 then the car runs great all day.

My question is this... What is it exactly that tells the IAC valve that it does not need to open and stay open... What tells it to close once it doesnt need the extra air?

Also, I replaced the coolant temperature sensor, so it isnt that. Thanks guys.

Anyone? I really need to get this fixed so my wife will stop taking my truck >.<

After owning an '89 with the 2.8L, with the exact same problem, and having the same frustrations over replacing every part imaginable, I came across something in my research of the wiring diagrams. The Coolant level sensor was tied into the same 5volt wire as the IAC & MAP, causing those to read as malfunctioning. You can test this theory by simply disconnecting the pigtail connector to the Coolant Level Sensor on the right (passenger) side of the radiator. If it resolves your problem, then replace that sensor, (with a new one that is NOT Borg Warner), and you are back up and running. Hope this helps!!