Extremely rough idle. Then Stall

[Jon89LE]

Started about 2wks ago. The first time it happened my car was on a forward incline and low on gas so i figured it was sucking in vapor bc as soon as i turned the car around it idled fine. Well that was 2wks ago. Hasnt happened since until 4nights ago. Running fine, shut it off, go into Sears, come out, nothing. Barely started and would not idle. It would idle very very rough and stall out. If i gave it steady med-heavy throttle it would idle real rough,but was just dumping fuel out the tail. As soon as i let off the throttle it would shut off. Finally after an hour it somehow stood idling around 1000rpm but sounded like i had a huge cam. My buddy followed me home and the whole time i could not get the car to rev in drive above 4k.

I was at a yard the other day so i picked up an ECM and dropped it in but it made zero difference. ECM had numbers matching my stock one so I know it was correct. None of the plug wires seems to have come undone and the fuel pump was replaced maybe a couple hundred miles ago. When it happened the second time at Sears the motor was hot and I just started it now before and after the ECM change with the motor cold and still same. Any ideas please let me know. On the way home no codes were set.

Since the occurence, I used a spare wire i had and am showing spark from all the terminals on the 3coils. I used a spare wire since i was unable to get to the back wires to unplug them and test. Since im showing spark im assuming the my coils/ICM are ok. What im not so sure on is the crank position sensor. EVen though i saw a spark, can it still be bad? After i tested the coils i tryed the car again and still the same issue. I had a buddy pick up new plugs and wires for me but this issue seems a bit drastic to be caused by a bad plug/wire. Wires and plugs were done this past summer. Crank sensor was replaced within the year.

Any ideas PLEASE let me know. Its cold as a mofo and i need the car for work this weekend!

Also, car will ONLY start with throttle applied and then die when throttle is removed. Without appling throttle car just keeps turning over feeling like its about to start but not starting.

Resistance for the Crank sensor at room temperature is 980ohms which is within spec. When placed in hot water around 200F read 1170ohms.

[tractorman]

It'll help quite a bit if you'll tell us what vehicle, year, and engine you've got. Just looking at your name, I'm gonna ASSume that you've got a 1989 3.1L engine. My best guess is your fuel pressure regulator. Check and see if it's dumping fuel into the engine through the vacuum line.

[Jon89LE]

Guess I havent been around these boards in a while. Car is an '89 GP w/3.1. I'll check for fuel in the line in the morning. Can a fpr fail this sudden?

[bszopi]

Just as a note...

IF the person has filled it out, you can always click on the Vehicle Info dropdown box below the user's name and see what car and engine they have.

There are probably several things that could cause similar things, but the FPR is a quick and easy check.

[Jon89LE]

I just checked the FPR and it doesnt seem like there is any trace of fuel on the vacuum line going to the TB or in the FPR itself. I checked the coils and was getting spark but could my issues be attributed to not strong enough of a spark? Im thinking about the fact that the car will start only even i have the throttle down but then just run like its burning raw gas. I initially though the mixture was not getting ignited but since there is spark maybe its not strong enough? Anyone know what voltage should be reaching the plug so i know what to set the gap on a plug checker once i pick one up?

[gpse3400]

Hey Jon Yeah that happend to me a few months ago only I couldnt get my car to run... Despite what you said i'm sure its the IGN module that went south. The chepest way to fix this, go to you local yard an nab a module and coilset from a 3100/3400 car anf transfere the mounting plates. If you do not have any codes then this would be it. one last thing, to make sure your fuel system is in check, you can pull you spark plugs see if they are wet. While you are at it you may as well change them, if they all dirty, wet, and black.

[prophiseer]

honestly, there's a ton that could cause those problems; but I'd start with the ign module. GM's older FWD's are notorious for roasting them out.

But, a faulty coolant tempurature sensor can cause the computer to go screw-ball on the motor

An IAC can cause similar problems, as well as a faulty crank sensor or MAP sensor.


You can try the tried and true "GM tap test" - if you can get the car to idle normally, take a large screwdriver and lightly tap on the electronic components with the handle of the screwdriver; if the idle and running quality changes drasticly, you've found a problem component.

[Jon89LE]

Hey Lorenzo. I figured you'd chime in eventually, haha. Its weird, the last time my ICM went the car just shut off on me while approaching an intersection on a downhill. Fighting to stop the car with those 10 inchers and no power was definitely fun. But im guessing the ICM can be bad without being totally dead. I wont have a chance to head to a yard for awhile but i believe theres an ICM on ebay that was brought to my attn by a fellow member. Is there any way to test the ICM with a meter? I know the resistance on the 3pin connector is within spec.

[gpse3400]

I dont know.I never rally bother to test them. They have dies out so many times I know what to expect out of them. Its like the alternator, it just does things that make it known. The DIS can die in many ways from complete and utter failure to just running one coil to making it misfire a specifc rpm... I guarentee you all you bad running problems that have to deal with cutting out, on running on 4 cylinders, whatever, is related to ignition. You can get at the bottom bolt of the module on on your car by removing the oil filter and oil pressure sensor and a nice long extension. disconnect the neg terminal on the battery. Everything else from up top.

[Jon89LE]

Oh shes not a virgin. That bottom bolts definitely gone already. haha. This will be the second replacement of the ICM. Being as I cant afford the $100 list im going to see if I can grab the one off ebay. Its amazing, i build the whole motor and the things which have given me headaches are the electrical components which have ALL been replaced more than once.

[geldartb]

if you want i have a spare icm let me know if you want it.

[Jon89LE]

How many miles are on it?

[Jon89LE]

Well ive basically done everything and its still running the same. Plugs, plug wires, and crank sensor were replaced. The set of coils/module on my car was put on my buddies 3400 GA and his car ran perfect so I know the module and coils are ok. The only other thing I have not gotten NEW was an ECM. I picked up the ECM out of a GP at the yard so its possible that both were bad although im finding that chance doubtfull. If I had broken a rocker or spring, could this issue happen? Ive got Crane springs and Comp roller tip rockers. I will be taking a video tonight of the car and posting it if possible.

[gpse3400]

Yeah...ok...the only other thing would be a bad injector, worn cam lobe, rockers out of adjustment(but then youd hear the velvetrain...). If the ijector were bad youd see the plug look almost new....

[Jon89LE]

When i did all the plugs they were all black and smelt like fuel. The only thing that could cause my sudden issue would be something in the valvetrain. Now mine has always been more noisy than stock. I cant remember what the recommended preload on the lifters was by Crane, but i remember adjusting them near the middle of the range. After the motor was built i ran the car without the valve cover on and the noise seemed to be coming for the rockers which I figured was normal due to their design. I have a video I did but its pitch black and the sound quality wasnt great so im going to see if I can do another one during the week in the daytime.