95 Buick Lesabre has intermittent stumble

[John Canon]

The ICM has a connector that does all the heavy lifting for the ignition system, including the cam and crank sensors, and the fuel injectors. When you change the ICM, the old harness connector stays with the car.

The 12 volt hot terminal carries 20 amps continuously, and it can get burned and melted. When the metal gets hot it loses its springiness and makes poor contact.

You have to look for this problem inside the harness connector. It is the heavy gauge pink wire at one end of the connector plug. Check all the other connector terminals for looseness or corrosion.

 

[HotZ28]

If all the injectors test with Ohms & noid light checks good on all six, I would suspect the cam magnet has disintegrated, or as mentioned, you have a wiring problem in that circuit. You need to do some further testing!
Part 1 -How to Test the Fuel Injectors (GM 3.8L)

Code 41: lost cam magnet in 3800

Part 2 -GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test

Page 2 of 5 : GM 3.8L Ignition Control Module and Crank (3X, 18X) Sensor Test. What Tools Do I Need to Test the Ignition Control Module (ICM)? Do's and Don'ts and Safety Precautions.

easyautodiagnostics.com

 

[imidazol97]

I'm reading a difference from the earliest posts of the problem, to which I responded, that
this occurred at higher speeds after warmup. TCC? Lean Mixture? Bad wires/plugs? Crossfiring?
And other problems that other posters have suggested.

Now it sounds like there might be two problems. The cold problem may be from the temperature
sensor that informs the computer what the coolant temp is and that affects the mixture. Using
a handheld scanner like my Actron (no good) will show the temperature that the computer
is being told.

I do not know if the 95 is capable of doing that. That's the period where the ALDC was changing...

 

[02LTD]

I'm reading a difference from the earliest posts of the problem, to which I responded, that
this occurred at higher speeds after warmup. TCC? Lean Mixture? Bad wires/plugs? Crossfiring?
And other problems that other posters have suggested.

Now it sounds like there might be two problems. The cold problem may be from the temperature
sensor that informs the computer what the coolant temp is and that affects the mixture. Using
a handheld scanner like my Actron (no good) will show the temperature that the computer
is being told.

I do not know if the 95 is capable of doing that. That's the period where the ALDC was changing...

1995 used OBD 1.5 which would require an adapter or you would have to get a scanner that’s capable of reading OBD 1.5

 

[Ghostrider20]

Does the engine idle normal? Does it stumble if you rev the engine in neutral? Cold or hot?

 

[landohanno]

Thank you all for your continuing input~ I have an ICM coming in sunday, and a cam position sensor to install as well. I will also inspect the wiring harnesses to the best of my ability. I have a multimeter, though I'm not deft at these things.

The car idles well. Sometimes it might wander just slightly, I assume that's the MAF? I think it's original.
It does not stumble when I rev the engine in neutral, cold or hot.

I'd also like to report that since replacing the coils yesterday, I've done two commutes and it has only stumbled that one time pulling onto the highway when cold, and then again today just briefly after a slight pull up a hill at 65mph about 25 minutes into the drive. Nothing at all like the 15-second long stumblefests that I was experiencing every long drive à la the video I posted in the OP. Frustrating if it is indeed two problems and I have only solved one of them (or neither!) but it may just be dumb luck that everything was almost normal. I thought I should mention this variance anyway.

 

[HotZ28]

I may be wrong, but from viewing all the previous post, I see no mention of replacing the ignition wires. Please update us, if that was accomplished. Thanks.

 

[landohanno]

Wires aren't replaced yet, though they are not original.

 

[landohanno]

I've ordered new ACdelco wires!! They will arrive tuesday at the latest

 

[HotZ28]

Now you are making progress! Old wires can put a burden on the whole ignition system & even cause the coils to fail.

 

[landohanno]

Well, another hot day in traffic and the symptoms are back. No luck with the new coils and wires. Guess I'll try the ICM swap next

 

[landohanno]

Whelp, the ICM didn't fix the issue. Got the new one installed, and the wiring loom and connector seemed fine at least on that end.

You can see here at 15 seconds as I'm idling in traffic, how the car stumbles, revs drop, and the volts drop (since the alternator disengages I guess?) before slowly coming back after a time.

 

[landohanno]

Update!

So, in poking around, I was snugging up every ground and unplugging every connector in the engine bay and checking them out. I get to the MAF, and the connecter seemed to have been packed with what I can only imagine is dielectric grease? Baffled, I soak it with contact cleaner and blow it out with compressed air.

Now: the idle has changed from what was normal-and-steady with that weird intermittent stumble as in the video above, to a wavy wandering mess that almost stalls. At speed, the stumbles have all disappeared... and then on longish drive, I get a CEL! The CEL is gone on a restart.

I have ordered a new MAF that arrives tuesday.

Could this have been two issues? Did I have a short in the connector, but also the MAF was bad? Why was it packed full of grease??? I am so confused.

 

[HotZ28]

Too much dielectric grease on contacts can cause, no contact! I have never seen that connection to the MAF OEM with dielectric grease in the terminals. Sounds like some previous owner wanted to go underwater driving, or lives in the swamp land??

 

[02LTD]

Update!

So, in poking around, I was snugging up every ground and unplugging every connector in the engine bay and checking them out. I get to the MAF, and the connecter seemed to have been packed with what I can only imagine is dielectric grease? Baffled, I soak it with contact cleaner and blow it out with compressed air.

Now: the idle has changed from what was normal-and-steady with that weird intermittent stumble as in the video above, to a wavy wandering mess that almost stalls. At speed, the stumbles have all disappeared... and then on longish drive, I get a CEL! The CEL is gone on a restart.

I have ordered a new MAF that arrives tuesday.

Could this have been two issues? Did I have a short in the connector, but also the MAF was bad? Why was it packed full of grease??? I am so confused.

I hope you ordered a HITACHI. Hitachi is the OEM MAF. Hitachi is stamped into the side of the throttle body.

 

[landohanno]

All right, to tie this all up with a bow: I've finally gotten it fixed up.

After the car was acting up, I pulled the ECM, stuffed it in the freezer. After a while plugged it back in, car ran much better. Replaced the ECM.

No problems since then!

 

[landohanno]

Whelp. Now I have an intermittent stall on startup when the car’s warm. Ugh. I’m about to lose it.

 

[G-15538]

Did you ever resolve this?