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Fast Idle Problem
Having a problem with my 2000 Buick Lesabre 3.8 V6, 98,000 Miles. 20+ MPG all the time around town.
New fuel pump last month. Also cleaned the Idle Air Control pintle and seat.
Idle is perfect at 800 RPM once it warms up.Just recently when the engine is started cold the engine idle will immediately go to 1400 and stay between 1200 and 1300 until the engine temperature reaches 185/F.then idle goes to 800.
Acceleration is normal just a fast smooth idle when cold. Outside temperature doesn’t matter it always races until water temperature reaches 185/fAny thoughts what sensor might cause this fast idle until warm?
Thank you in advance
Bob
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[quote=”propcop” post=56723]Fast Idle Problem
Having a problem with my 2000 Buick Lesabre 3.8 V6, 98,000 Miles. 20+ MPG all the time around town.
New fuel pump last month. Also cleaned the Idle Air Control pintle and seat.
Idle is perfect at 800 RPM once it warms up.Just recently when the engine is started cold the engine idle will immediately go to 1400 and stay between 1200 and 1300 until the engine temperature reaches 185/F.then idle goes to 800.
Acceleration is normal just a fast smooth idle when cold. Outside temperature doesn’t matter it always races until water temperature reaches 185/fAny thoughts what sensor might cause this fast idle until warm?
Thank you in advance
Bob[/quote]
This sounds as if the IAC is misadjusted. Do the adjustment procedure in the service manual and idle should come down.
Let us know what happens.
Thanks for the suggestion to reset the IAC. I did as suggested by turning the key off then on, I also replaced the computer water temperature sensor with a new Delco sensor ($24.00).
Fast idle (1300 RPM) continues until engine temperature reaches around 185 or higher then the idle returns to normal about 850 RPM
Maybe intake air temperature sensor?
Thanks for the reply college man
I believe there are two water temperature sending units. I replaced the one just below the thermostat housing, which is the one that communicates with the computer?
My online manual doesnt show where the other gauge sending unit is located for the instrument pannel temperature gauge and the I.P. guage appears to be working normal.
One couldnt ask for a better running car once the operating system temperature is reached (190/f). I’m afraid the brakes will wear out if this keps up.
Thanks in advance for you rhelp
[quote=”propcop” post=56885]….Fast idle (1300 RPM) continues until engine temperature reaches around 185 or higher then the idle returns to normal about 850 RPM….[/quote]
This is normal, your engine should idle fast until it gets to operating temp (about your 185 reading), then it settles down to warm idle speed.
The intake air temp sensor hasn’t anything to do with this. The sensor involved is the coolant temp sensor connected to the PCM. The PCM uses that info to decide how far to open the IAC.
If the engine is cold idling too fast, then the IAC is either opening too far, or the pintle may be sticking. Try tapping on the IAC gently during cold idle. If the idle speed drops, the pintle is sticking, and the IAC may need replacement. (I’ve never been successful cleaning one.)
Keep us updated.
moparfanI agree, it does sound normal. Perhaps your base idle was adjusted offsetting where it should be which can mess up the fast idle when you start the engine cold. They engine would normally idle from 12-1300rpm when cold.
Thanks for the reply’s guys, it means a lot to have someone to reach out to.
I did purchase a new Delco Idle Air Control valve but still the engine races when started.
The racing engine behavior when cold only recently started, it never ran this way until a short while ago. Yes it would run at 1200 RPM at first but quickly fell to idle speed 800 RPM, maybe 30 – 60 seconds, now its taking 7 – 10 minutes or when engine temp reaches 185/fAs I said before the engine runs perfectly once it reaches operating temperature.
New curve, last week the system threw a code PO442. (Small leak during vacuum Emission test) Engine still runs perfectly. No stumble, no hesitation, smooth idle, good gas mileage.
Local Massachusetts Inspection garage guy suggested purchasing a new gas cap from a Genuine GM Dealership, so I did that. Said he has lots of issues with aftermarket gas caps.
On several occasions I tried probing vacuum lines, manifolds, etc with propane, when the propane didn’t show any results I tried probing with carburetor cleaner. Both the propane and carb cleaner didn’t show any vacuum leaks.
Parts recap:
(Thermostat), (Delco IAC Valve), (Delco Water Temp Sending Unit), (Delco Fuel Pump), (Delco Gas Cap)
I also have a 2003 Buick LeSabre with the same engine and does not race like the 2000 LeSabre.
Thanks Eric
PO442 error code turned out to be a small section of rusted vapor returm line under the car. Cut out bad section replaced with rubber fuel line and stainless hose clamps.
Did you ever figure a way to help your fast idle?
I wonder if you cleaned your throttle body?
Also, I believe the reset for the IAC is a little more than turning the key on and off, I think it’s more like on for 10 secs, off for 30, on for 10 and start, you may have done something like this but just shortened the written answer.
Last question, do you have a ELM327 bluetooth device plugged in on this car? Since you knew the temp so precisely, I thought you might have some sort of scanner hooked up, and specifically, do you leave it plugged in all the time?
I only ask because I had one hooked up for an extended period today to my 1996 Buick Regal and I also got an emission code, though not the same one. My problem also presented with cutting out symptoms, it flashed the Check Engine, and the Oil Low *(though oil was verified A-OK), and I had to actually remove my ELM327 to solve my problem. Evidently mine wasn’t fully compatible, or perhaps faulty, but I just thought I’d ask. I realize your emission code was solved and is probably not related, but I can testify these devices CAN actually CAUSE a problem.
[quote=”propcop” post=58340]PO442 error code turned out to be a small section of rusted vapor returm line under the car. Cut out bad section replaced with rubber fuel line and stainless hose clamps.[/quote]
Nice job with finding and fixing the vapor line. 🙂
I just looked up your thermostat. The OE temp is 195F
the list does give an alternate of 180F That could be
part of the problem. Its possible that its messing with
the computer. The part store may have given you the wrong
thermostat.Make sure you don’t have any vacuum leaks. The IAC might be struggling to overcome a vacuum leak. Check all rubber hoses for holes or splits.
Eric has a good video about this here http://www.youtube.com/watch?v=9CPqbaSgcok
I did clean the Throtle body and MAP sensors with a spray can product made for the job. I also did the checks for engine vacuum leaks as suggested by Eric.
This engine runs like a Swiss watch hot or cold, I couldnt ask for a better running engine.
The car just hit 100,000 last week and I’m still using synthetic oil. Getting 22 – 23 MPG around town with no highway drivingToday I replaced the air intake temperature sensor. With the new sensor installed the cold start idel speed dropped from 1400 to 1250 RPM, more in line with the way it used to be. I havent driven the car yet but expect it to be just fine.
Of course were in the summer months now and real cold weather starts and engine RPM data will have to wait a few months.
I will also try re-calibrating the IAC motor using the times reccomended by Buicklunch, the last time I did the procedure I did not wait that long.
I also use an OBDII interface that allows real time monitoring on a laptop of many engine functions including engine water temperature in real time.
Lets see what happens …..
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