quote:

Originally posted by David Lee:
1998 Buick 3800 non super charged. Plugs are new AC. Shes been at rough idle about a week now. I am hoping its not intake and plenum, even though thats not too costly. Doing a carb cleaner check tomorrow. I found a vac line diagram to follow. I actually hope its IAC valve or EGR. Had it scanned tonight but check engine light was gone and no stored codes. Anyone have knowledge of the 3800 ?

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Originally posted by Excam_Man:
Try cleaning the air intake throat.

98 still has the aluminum intake, right?

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Originally posted by shovelhead:
Check coil packs, spark plug wires and spark plugs? I'm assuming you checked those first. Despite the fact that you just replaced them make sure you did not accidently crack one.

I'm assuming you checked for arcing wires and coils also? No codes leads me to believe that it's in a non SES indicator sensed part. I don't remember if that is an electronic EGR valve, if not it could be stuck slightly open by carbon buildup and not throw a code. I doubt the IAC is involved, that should throw a code as it is fed thru the PCM.

quote:

Originally posted by bettysnephew:
A mechanic I worked with years ago diagnosed vacuum leaks with an unlit propane torch. He would set the flow rate very low and run the nozzle along vacuum lines. When the leak was located the idle would smooth out due to the mixture getting better. Don't know if this will work on later model vehicles but it sure made quick work of vac leaks back when.

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Originally posted by Excam_Man:
The black plastic intakes are known for cracking around the EGR tube. Then antifreeze goes in the intake valves.

quote:

Originally posted by shovelhead:
BTW, a little FYI. We had a 92 Bonneville with a 3800 that had the unnerving fault of stalling out while driving. Just shut down for no reason, no SES codes. I worked in a Pontiac dealership at the time, our techs could find no reason for the shutdown. Really fired up the wife as it shut down on her in the fast lane at her customary 80-85 mph on I-96 one morning.

I found it one day after my wife got a new car and I took it over. Stall out, I pulled off the road. Car cranked normally, no fire. Cycled the ignition on and off. Second crank I am looking at the tachometer, no movement of the tach needle. Suddenly as I am watching the needle, it jumps up, car starts up. Got back to work, replaced the crank sensor, all good after that.

That failure would not trigger a SES light as the crank signal was lost to the PCM. Acted like the ignition switch was turned off, PCM read this as shut down.

This might save others some grief with diagnosis, I hope.

quote:

Originally posted by David Lee:

quote:

Originally posted by Excam_Man:
The black plastic intakes are known for cracking around the EGR tube. Then antifreeze goes in the intake valves.

Only coolant loss is up front at a fitting or hose. I keep after that.

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Originally posted by shovelhead:
From memory I think that if the IAC is stuck open it increases the idle speed and sets a code as the pintile reading does not match the TPS.

quote:

Originally posted by shovelhead:
I retired from GM dealership parts departments the end of June, I figured 47 years in it was enough for any person..........