'91 randomly stalling while driving

[Grayman]

I have a 91 Lebaron with a 3.0 V6 that will randomly stall whilst driving. Following are my observations of the problem over the past few months.

• A stalling event is usually preceeded by sporadic missing under medium to heavy accelleration
• Becomes completely unresponsive to throttle immidiately before it stalls - sometimes idles for several seconds before dying completely out
• On two seperate occasions, it would restart (first I always switch it off to clear the computer) and idle, but would get very rough and die without picking up rpms if i pressed the accelerator
• Once it restarts, it usually runs ok and seems to have full power again
• The two times it died and refused to immidiately restart, it took 3-5 minutes to get a successful start that would accelerate; also, these two times were preceeded by slightly harder than normal driving (go figure, it happens when I'm in a hurry)
• Between the two major stalling events, I drove it twice in excess of 110 miles w/o any trouble and little or no missing
• It frequently has smaller events where it will stutter a couple times while ignoring my input on the throttle before dying completely; recovery is simply shifting to neutral, switching it off a few seconds, and restarting it... then usually runs ok or runs w/ occasional missing
• Some days it runs with no stalling and no missing, even under heavy acceleration.

Ok, there's the problem as i've experianced it... I'll give ya a little info about the car here too to assist ya in helping me out!

• car has a little over 110k miles
• recently replaced original distributer cap (in middle of the problem, no differance), also verified no debris in optical pickup & connections to pickup in good condition
• looses over 1 qt of oil per change (needs new gaskets and a valve guide job, i know... )
• Has had weak vacumme for several years (HVAC dampers reset under heavy acceleration), long before this problem arose

I personally am thinking that it may be the throttle position sensor, and a relative suggested it may be a fuel filter. Does anyone know a way to check a TPS (i have access to a multimeter and a oscilliscope) or have any other ideas as to what may be the problem?

I'm more of a GM person, and when my '89 cavalier did this it was a bad ECM. I put the scope on the ignition module on this car and all seemed very stable, leading me to think the problem is elsewhere. I'm planning to change the fuel filter this weekend as a routine maintenance item, but I'm having doubts that it would cause the lack of throttle responce prior to stalling. (or is it already fuel starved and just getting pushed by the transmission for a few second until the pressure drops, then stalling?)

[94LebConv3La604]

Was actually going to suggest a fuel filter change...can't hurt and is cheap enough and may even be the problem. Just for the hell of it, try the on-off-on-off-on cycle to see if any codes pop up.

[Grayman]

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### UPDATE ###
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Ok, I got the engine codes this evening, here they are in the order it output them:

12: # keyons since last fault
51: keyons... (or O2 lean?)
25: auto idle speed motor circuit
41: alternator field not switching properly
47: charging system voltage too low
55: end

The 41 & 47 codes were likely set a couple months ago when I took it to the mechanic to replace a broken power steering rack line; i removed the belts to avoid burning out the pump.

The 51 appears to be the descriptor for the 12 code, meaning 51 keyons.

That leaves a code 25 to look into; it seems to be idling ok, so could this circuit (code) include the Throttle Position Sensor?

[Grayman]

Well, I replaced the fuel filter this weekend. It didn't seem overly clogged, but the car seems to run a little better; sounds a little smoother and has a bit better accelleration. I thought I felt a few hesitations once while accelerating heavily; could be same problem, not sure. Also, how do you reset the codes in the computer once you've read them? I'd like to reset it so it's easier to tell what code sets should the problem repeat itself.

[94LebConv3La604]

Think you need a device to actually do that or take it to a dealer....also I believe they clear after a certain amount of key turns.

[Grayman]

Ok.. a few updates here...

1.) I found I can clear the computer easily by leaving the battery disconnected for a bit. (went out to dinner)

2.) Noticed that when it acts up, I can give it light gas (just cracked past idle) and it will run, any more or less and it immidiately dies. Pumping the gas hard several times will cause it to sputter to life for a few seconds, then die again. After about 20-30 seconds of this, it dies altogeather, refusing to start and run for several minutes.

3.) The problem now only occurs during cold starts; once it's been run it seems ok for the day.

4.) No codes set after a couple times of this problem.

5.) I decided to start checking sensors, but so far the only one I've gotten checked is the TPS, it seemed ok judging by its smooth response on my scope.

If anyone has any ideas of what to check from here, please let me know!!!

How I feel when I look at the car!! ->

[94LebConv3La604]

Granted your alternator should provide enough power while the car is running....but just for shits and giggles, how old and in what condition is your battery?

[Grayman]

If I remember correctly, the battery is a couple years old. It still cranks over quite strongly and the terminals are clean. Voltage gauge sits about center (~14V).