Excessively High Idle Speed/3.1L Chevy V6?

[Jelly]

Well, the truck's back home for awhile (it's of more use there hauling/towing stuff and being off-road) and I'm driving a Chevrolet Lumina with the 3.1L V6. Has around 135,000 miles on it.

It has an excessively high idle speed. Upon cold startup, it'll run anywhere from around 1200 up to around 1900 at idle, in park. It won't flucuate around, just stay at one level, but that level varies with each time you start it up.

As soon as you drop it down into gear, it'll drop down to around 1000-1200. (All these are just off the top of my head as I haven't got to spend much time with it yet)

On hot idle, it'll only go down to around 1000 (indicated rpm).

What could be causing this?

 

[pitzel]

Check/clean the throttle body, idle air control actuator, and ensure that you have no vacuum leaks. Also check the coolant temperature sensor.

Seriously though, what you are describing is pretty 'normal' behaviour for the 3.1L V6 of the late 80s/early 90s. The ECU sets the car at a relatively high idle just to warm it up more quickly, and as the coolant temperature rises enough to become adequate, the engine does slow down somewhat into an idle around 650-800rpm.

Another thing you can do is known as an 'idle re-learn'. You can find the procedure on http://www.w-body.com . This will reprogram the ECU and adjust your idle speed accordingly.

 

[Jelly]

quote:

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Originally posted by pitzel:
The ECU sets the car at a relatively high idle just to warm it up more quickly, and as the coolant temperature rises enough to become adequate, the engine does slow down somewhat into an idle around 650-800rpm.

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Thanks for the link.

Yeah, I understand the ECU setting a higher idle, but this is too high! Plus, it won't drop back down the 650-800. It'll drop down to around 1,000 in drive, but in park, it'll go back up to around 1,200-1,500.

 

[pitzel]

quote:

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Originally posted by Jelly:

quote:

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Originally posted by pitzel:
The ECU sets the car at a relatively high idle just to warm it up more quickly, and as the coolant temperature rises enough to become adequate, the engine does slow down somewhat into an idle around 650-800rpm.

---

Thanks for the link.

Yeah, I understand the ECU setting a higher idle, but this is too high! Plus, it won't drop back down the 650-800. It'll drop down to around 1,000 in drive, but in park, it'll go back up to around 1,200-1,500.

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What year is your car anyways? Just interested in whether we are discussing the 3100 or the 3.1L V6.

 

[Jelly]

1995 with OBDI.

Just read on the link you posted about Gumout Air Intake and Throttle Body Cleaner.

Do you know which store carries this stuff?

Car will be getting a dose of Gumout Regane in the next couple of weeks...

 

[427Z06]

Last 3.1L V6 I saw with that symptom had a severe manifold-head gasket leak.

 

[TomH]

Have you checked to see if the ECM has any stored trouble codes? A bad CTS(coolant temp sensor) or IAC(idle air control) valve will cause the problem you are describing. Either of these two parts going bad may not make the SES light glow, but the codes may be stored anyway. I sold a lot of CTSs and IACs when I worked for AZ, and they're fairly inexpensive parts at that.

 

[T-Keith]

Your right, that idle is too high. Check for vacuum leaks and clean the throttle body with an air intake cleaner.

Don't use any fuel injector cleaners if it's a late 80's or early 90's model, or kiss your fuel injectors good bye.

-T

 

[Jelly]

quote:

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Originally posted by 427Z06:
Last 3.1L V6 I saw with that symptom had a severe manifold-head gasket leak.

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Doesn't use any coolant (as far as I know).

quote:

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Originally posted by TomH:
Have you checked to see if the ECM has any stored trouble codes?

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Yep. Had a code 76 and 77 which is digital EGR valve related.

quote:

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Originally posted by T-Keith:
Don't use any fuel injector cleaners if it's a late 80's or early 90's model, or kiss your fuel injectors good bye.

-T

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It's a 95. Why no fuel system cleaners?

 

[T-Keith]

If it's a 95 your OK older models were harmed by fuel system cleaners.

 

[pooter WS6]

just spray some water around the mating surface of the intake manifold to the head or to the lower intake manifold. If the idle changes when you spray the water, you have an intake leak. Replace the gasket and you are good as gold.

 

[pitzel]

quote:

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Originally posted by Jelly:
1995 with OBDI.

Just read on the link you posted about Gumout Air Intake and Throttle Body Cleaner.

Do you know which store carries this stuff?

Car will be getting a dose of Gumout Regane in the next couple of weeks...

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Hmmm. After you run that stuff through your engine, you might want to consider replacing your oxygen sensor. If you get the oxygen sensor all contaminated with carbon, you may as well kiss it goodbye. Keep your old oxygen sensor and install it for occaisons such as the cleaning you give it with such products. And while you're checking your system for vacuum leaks, pull the PCV valve and make sure its still working.

 

[TomH]

quote:

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Originally posted by TomH:
Have you checked to see if the ECM has any stored trouble codes?

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Yep. Had a code 76 and 77 which is digital EGR valve related.


Knowing that, the first thing I'd do is remove the EGR valve and clean the carbon out of the passages, as I'm sure being 9 years old it's full of the stuff. After that, reset the codes by removing the negative cable for about 30 secs. and see if the code(s) and/or the problem reappear.

 

[Jelly]

UPDATE - Went out and took a "test drive", this time paying close attention to it's idle characteristics...

Upon startup, RPM's immediately went to about 1900, and slowly went down to around 1100. This is in park.

Once in drive, RPM's dropped to around 900-1000.

At stoplights, RPM's remained at 1000-1100.

Once I stopped somewhere and put it in park, RPM's rose to 1500 in one place, 1100 at another, and a little less than 1000 at the third place.

RPM's even went down to around 800 or so stopped at a redlight, with vehicle in drive and foot on brake.

As you can see, the idling RPM's are vary sporatic at best. Also, the RPM's would flucuate just a little bit.

 

[427Z06]

quote:

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Originally posted by Jelly:

quote:

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Originally posted by 427Z06:
Last 3.1L V6 I saw with that symptom had a severe manifold-head gasket leak.

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Doesn't use any coolant (as far as I know).

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Vacuum leak, not a coolant leak.