High idle, then low rough idle issues again

[wlkstout]

On my 1991 3.1l Cutlass Supreme all things started again yesterday. Will get idles in the 2000-2500rpm Range then I will come to the stop sign holding my foot on the brake and it'll drop down to 200 to 500rpm idling rough sounds like it's missing again. Did get code 22 and 35.

 

 

My question is would the intake gaskets give so soon? I replaced them all last fall along with new head gaskets(all Felpro's). I get a brief smell of egg,,could it be the cat? Or could it be the ECM? ECM is a rebuilt one that is in it. I do have a voltage meter and checked for electrical problems but the wiring seemed ok. I have not gotten a scan tool yet so I have not looked at any data, budget restraints. It has been running flawlessly latly, getting 22mpg at last fill up around town. So frustrating.

 

IAC is couple months old. I did replace the TPS yesterday, thinking it could be shot but didn't help.

 

Any ideas?

[wlkstout]

Since gasket were replaced, I have put roughly 6k miles on the car. No overheating issues.

[Padgett]

I have similar problems and a new IAC coming in. It is so erratic that it is hard to believe a vacuum leak but once it settles down it is fine. Do get the 35 (idle over 1500 for a minute in closed loop) but not the 22 . IAC command, desired idle, and TPS all look fine but idle is high but erratic for 3-5 minutes from cold start. Rapping on IAC has had no effect.

 

What does your MAP read when idle is high ?

[wlkstout]

I did get the 35 and 22 on mine that's why I replaced the TPS. This morning on the way to work it was hard to start. So I change the AIC back to the original one that it had last year and it ran fine coming into work. So we'll see how it does this afternoon. I am leaning more towards an electrical issue. We

[wlkstout]

But after I replaced the TPS all I got was the 35 AIC High idle error.

[Padgett]

and all 35 means is that the idle was high, not that it was the IAC.

 

That said the USPS says I will have a replacement IAC on Saturday and will try that. Hate just throwing parts at a problem but is a lot easier than replacing the lower gaskets ( and testing a few bolts I could reach removing the small cover, none were loose). My experience with vacuum leaks is that they do not vary over 1,000 rpm.

[wlkstout]

Okay with the new TPS sensor the car is not holding any high idles anymore(2000rpms). Right now it's running fine except for when you come to a stop sign or stop light then I'm getting erratic low(100-800rpms) end idles but if I bump into neutral it will level off at 700 rpm and be smooth. It is acting like it wants to stall but if I give it just a tiny bit of gas levels off. Only doing it when in gear.

[Padgett]

Have you cleaned the IAC ?

 

See "LQ1 high idle" for my latest but seems to have been a dirty contact or sommat on the MemCal. Blew a new PROM and ran for two minutes. Then 3k idle, then NADA. Cleaned everything involved and now runs fine, idle within 100 rpm of command. Starts instantly. Running 183-186F with one fan, both with AC. Happy Happy, Joy, Joy.

[wlkstout]

I had to clean them but what I did the other day was put a different AIC in it. It ran fine for about hundred miles with the newest one I bought, it was a brand-new one that I bought a couple months ago. Then yesterday it started back with a low and high idle, 400 to 800 RPMs. I did it about three times when stopping on the way home from work but then it cleared up. I think today after work I may look into your prom and ECU connections findings and see if it makes any difference.

[Padgett]

IAC (idle air controller) ? Did you clean out the IAC passage in the throttle body with carb cleaners or a solvent ? Have seen the passage get gunked up with sticky stuff.

 

Do you have any way to monitor things like trouble codes, IAC command, injector pulse width, and O2 transitions ? Is the idle fluctuation in open loop, closed loop, or both ?

 

My idle is much better but still stays high (1500 rpm) when I put into neutral coming up to a stop but then idles down when stopped so pretty sure it is a command. Wonder if DFCO, I had to disable that when we put a Getrag in a Reatta.

[Nas Escobar]

My idle is much better but still stays high (1500 rpm) when I put into neutral coming up to a stop but then idles down when stopped so pretty sure it is a command. Wonder if DFCO, I had to disable that when we put a Getrag in a Reatta.

Are you sure there's no corroded or broken plastics, rubbers or connectors? I swapped my ECU and i idle between 800 and 1000. All my vac lines are replaced or patched and all are ran in accordance with my diagram on top of the radiator support

[Padgett]

Reasonably certain: put into neutral coming to a stop and idle is around 1500 until stop, then drops to 800-900. Matches a DFCO subroutine for the 3800 I had to disable. Only problem is the TunerCat maps do not show a DFCO for $DF.

[Nas Escobar]

Hmm that's rather strange.

 

Your replacement PROM didn't come out of a 5 speed did it?

[Imp558]

I think today is Victoria Day, or Monday was, I don't fully understand how the day is derived.

At an rate, happy Victoria Day or belated Victoria Day to my friends to the north.

[Padgett]

Yes five speed manual code BCFA/1441.

 

Idle IAC is in 20s but can see it increase to mid 30's/1500 rpm costing up to a stop in neutral and when speed drops to zilchish the IAC comes back into 20's and idle drops back down.

 

Shot at nermal idle.

 

Do have something called "Idle spark enable threshold" that is set to 2mph but suspect there is a DFCO setting somewhere but not in the TC definition.

 

 

 

[Imp558]

so strange that post was supposed to be in whatever

[wlkstout]

IAC (idle air controller) ? Did you clean out the IAC passage in the throttle body with carb cleaners or a solvent ? Have seen the passage get gunked up with sticky stuff.

 

Do you have any way to monitor things like trouble codes, IAC command, injector pulse width, and O2 transitions ? Is the idle fluctuation in open loop, closed loop, or both ?

 

My idle is much better but still stays high (1500 rpm) when I put into neutral coming up to a stop but then idles down when stopped so pretty sure it is a command. Wonder if DFCO, I had to disable that when we put a Getrag in a Reatta.

I have cleaned the passageways. No I don't have any monitoring tools. With the newest aic it ran fine for a few days but no has an ever so slight fluctuations 600-900 rpm idle when in gear but not all the time. And will again stop when bumped into neutral. Haven't gotten around to pulling ecm and checking connections. Hopefully this weekend.

[Padgett]

Well neutral is lower drag than drive but without being able to look at the parameters it is almost impossible,

 

And unlike OBD-II (under $30 if you have a smart phone), a proper diagnostic system for ALDL is not cheap ), a laptop link is between $55 and $80 and Real Time software is about $40. You might be able to score an OTC-2000 or OTC-4000 for less but have to make sure it includes the GM 12 pin cable and a cartridge that covers your year.

 

Advantage with software is that you can set it to logging many parameters, take for a drive, & later review what it was doing at each point of interest.

 

Or you can throw parts at it until something changes.

[wlkstout]

Since last post. Have had no issues. Everything has seamed to resolve itself. Hopefully for good this time.