2002 Buick fast idle

dfast

Newbie
Joined
Dec 26, 2010
Messages
2
Points
1
Make
Buick
Model
Lesabre Custom
Year
2002
Miles
86000
Engine
3.8
I have replaced all throttle body sensors twice. Replace with new throttle body with sensors. Replaced IAT sensor. Problem fast idle can range from 1500 -3000 RPM. Key down and wait 15 seconds then rekey to start / run and idle goes back to 850 rpm. No events. Occasionally service engine light will come on. But no stored codes / events. I clear codes with Actron Model CP9580A handset. All though none are stored. Dash service engine light goes out.
 

JackC

wrench
Joined
Nov 14, 2006
Messages
1,665
Points
38
Location
Nothern California
My first thought is an intermittent vac leak. A malfunctioning EGR valve can act like a vac leak, especially at idle.

.A no cost diagnostic trick is to make a block off plate out of metal that can be temporarily placed between the EGR and the intake.
I usually make that plate out of soda can aluminum or similar.

If that solves the problem, the EGR is intermittently staying open at idle when it should be closed and you need to replace or repair the ERG valve.

If the plate does not solve the problem, we can go further.
 

grcauto

Hero Member
Joined
May 29, 2014
Messages
711
Points
28
No codes? Either the PCM or scan tool are having a problem.
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
11,065
Points
63
Location
St-Hyacinthe, Quebec, Canada
No codes? Either the PCM or scan tool are having a problem.
Yeah, that caught my eye also.

Maybe try a cheap elm 327 off of ebay or similar to rule scanner out.

I like jacks idea, and my $.02 is to stop throwing parts at the car and follow basic trouble shooting, such a, when it is fast idling what does a vac gauge say. Vac gauges are relatively cheap and or maybe can be rented at your local autozone or canadian tire depending on where your from.

Here is a chart for idle system, just swapping parts will MAYBE fix something sometimes, but following logic never hurts. ;)

Try this chart to help pin down this key off then on again go away problem. You would be surprised at how many wire and pin proplems thee cars had back in the day at the ecm slash pcm.

the pdf is called custom lesabre. :)

PS, having access to live data is always good your actron is just a code reader with limited capabilities, but it does live data, so look at that. What are readings at time of fast idle. I dont think the actron has the ability to see desired idle from pcm, that is always something I look at. What does the pcm want in regards to what your getting. But I could be wrong, never used an actron thing before, so I could be talking out of my left butt cheek right now.

.
 

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