Intermittent rough idle, stalling

Re: Intermittent rough idle, stalling

Postby 95AstroLT [OP] » October 31st 2020, 6:34pm

Leeann_93 wrote:When running, wiggle the wires - pull back, push in, twist slightly. No change at all in running?


No change. I didn't twist the wires but did push and pull. Did it gently as MechBob cautioned.

Stumbling/stalling is definitely more likely the longer the engine idles, guess that's a clue. Perfectly fine following cold start. After a 45 minute drive yesterday I let it idle in gear for 2 minutes. First minute perfectly fine, 2nd 60 seconds 2 slight stumbles. Its trying to tell me something, but what?

I'm going to further investigate IAC. Just ordered one from Rock Auto.

Truly appreciate the ideas, please keep them coming!
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Re: Intermittent rough idle, stalling

Postby Bossman » October 31st 2020, 7:02pm

Just a suggestion if you are going to replace the IAC, get the acdelco unit.

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Re: Intermittent rough idle, stalling

Postby 95AstroLT [OP] » October 31st 2020, 8:12pm

Bossman wrote:Just a suggestion if you are going to replace the IAC, get the acdelco unit.

Mike


Oops, too late. Oh well - replacement should at least provide "different" characteristics if the one on it is bad. And at a 3rd of the price. If el cheapo only fixes it for a week or something it will point to IAC being the problem. If no change, I know to keep searching for the problem.
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Re: Intermittent rough idle, stalling

Postby AstroWill » October 31st 2020, 8:54pm

I have had good luck with the aftermarket ones as well, so I wouldn't stress it.

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Re: Intermittent rough idle, stalling

Postby 95AstroLT [OP] » November 8th 2020, 10:25pm

Received the new IAC and put it in.

Change it made seems to be when the engine starts to stumble the idle reacts more quickly resulting in a less noticeable stumble and so far no stalling. So old IAC was definitely a contributing factor.

But I still want to find the cause of stumbling. I let the van idle 20 minutes while I was waiting to pick my daughter up from work. Stumbles seemed to come in waves - steady idle then 2 or 3 stumbles in 10 seconds then steady again for 15 - 20 seconds or more.

I say "steady" instead of "smooth" because the engine has a lot of vibration at idle - doesn't rattle the mirrors but if stuff is on the console it will rattle. It's done that for quite a while. Of course we had very bad idle when the spider needed replacement, but afterwards it still vibrated the same. Replaced the motor mounts and transmission mount a couple years ago, really didn't help. I mention this vibration detail because it could be related.

For now I'm running more Sea Foam in case its the fuel injection.

So I'm still soliciting ideas if you have any at all. At 303 K miles surely the engine is worn but never had high miles cause this on any other car I've owned. Still wondering if timing chain could be super sloppy but haven't checked it yet because I read 4.3s don't have much of a problem with those - but feel free to point to that if you have experience.

Thanks again!
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Re: Intermittent rough idle, stalling

Postby 95AstroLT [OP] » November 11th 2020, 3:58pm

Update: Still running OK but not great. Added 1 can Sea Foam to 1/3 tank of gas. Seems to run smoother, but that's subjective and I've been fooled before. Just filled up this morning, nothing added to gas, we'll see.
As far as I know (other family members drive it more than I do) it has not stalled since the new IAC valve, but it does occasionally stumble although not as badly as before. We only drive it around town, perhaps more than just a few miles of interstate driving would make a difference.
Thanks again. Any ideas, of course let me know.
1995 Astro LT 303,000 miles
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Re: Intermittent rough idle, stalling

Postby Leeann_93 » November 11th 2020, 10:33pm

If you have a decent hill somewhere around you, perform an 'Italian tune-up' - take it to the bottom of the hill and punch it all the way up the hill.
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Re: Intermittent rough idle, stalling

Postby Astroratsun » March 27th 2021, 3:01am

I like the Italian tune up! Too funny!
Two thoughts, assuming its still doing this... is there water in the gas tank?
Methyl hydrate would solve that...
Second I had a stumbling at idle issue which turned out being the plugs and wires!
Runs smoothly now!
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Re: Intermittent rough idle, stalling

Postby Mmusicman » March 27th 2021, 6:56pm

In the "olden days"... I would have possibly suspected "vapor lock".. or "fuel flooding" or "fuel boil".
But I doubt this applies to fuel injection... :D
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Re: Intermittent rough idle, stalling

Postby Coaster » March 27th 2021, 8:28pm

the 95 has at least two proms, i have both an early and a late one. the early idles at 600 rpm and has high shift points. the late one idles at 650 and has low shift points. with 3.73 gears i prefer the late one, plus the idle is better. the late one has a modified egr program too. it "chomps" the carbon by cycling fast vs acting like a vacuum egr and holding open.

one thing i noticed running tunerpro rt was that if i saw my egr get stuck open at 0.3% i knew it would die at idle. i finally got a new EGR and it have never stalled once.

my point is that i chased this same stall for years. i fixed it
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Re: Intermittent rough idle, stalling

Postby the_bruce » July 21st 2021, 3:52am

This can also be the ignition control module. It will lead to bad spark and incomplete combustion. I have had two bad ICMs in the last three years. First one was intermittent and dogged me for more than a year with frustrating behavior, most recent one failed all at once and van would not drive. Would hardly start. Strong smell of gas in the cabin after multiple start attempts and stench of hydrocarbons in exhaust. After replacing ICM in both circumstances the van runs smooth and as good as new. Just a suggestion if no other solutions are working. Easy to access with the doghouse off.
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