car revs on its own?
#1
car revs on its own?
I noticed recently when stopped at a light or in park, the tach goes up to about 1000rpm all by itself. Just wondering what thats all about. My last tuneup was maybe 5 years ago. Time for another one?
#4
#6
Re: car revs on its own?
#7
Re: car revs on its own?
Idle air control sticking? Any codes displayed? Try taking the air intake hose off and see if you still have the same idle?
94 Z28 A4 known mods... reworked ported heads/intake. Cam, 3" cat back flowmaster. unknown PCM tune. still researching car. ...
1990 RS HO 305, TH350(shift kit). 4 barrel carb, Cam, Long tube headers.
94 Z28 A4 known mods... reworked ported heads/intake. Cam, 3" cat back flowmaster. unknown PCM tune. still researching car. ...
1990 RS HO 305, TH350(shift kit). 4 barrel carb, Cam, Long tube headers.
#8
Re: car revs on its own?
Might be a good idea to run a data log to see how the PCM is responding to the change in idle speed, or if there is erratic input from a sensor or actuator that is driving the RPM increase. Look at the Scan9495 data logging thread in the "stickies" at the top of the "Computer Diagnostics....." forum.
#9
Re: car revs on its own?
Haven't gotten a chance to check anything yet. I also noticed lately when cruising on the highway at 60, when I want to pass a car, I give some gas and the car shakes and hesitates. I ease off the gas and try again and it works ok. What's that all about?
#10
Re: car revs on its own?
Sounds like a vacuum leak but like Fred said, data log will tell a lot.
Old school thought - If you are good with a vacuum gauge, that might help too but remember, a modified engine's vacuum MAY differ from the normal readings from a unmodified engine. My engine pulls 10" of vacuum at idle (1000rpm) but is steady. Check this site out. Might help now or in the future but good info.
How to Use and Interpret a Vacuum Gauge
Old school thought - If you are good with a vacuum gauge, that might help too but remember, a modified engine's vacuum MAY differ from the normal readings from a unmodified engine. My engine pulls 10" of vacuum at idle (1000rpm) but is steady. Check this site out. Might help now or in the future but good info.
How to Use and Interpret a Vacuum Gauge
#11
Re: car revs on its own?
Looks like its the idle control. New part has been ordered. Would that also correct the issue with the car hesitating at times on the highway when giving some gas?
#12
Re: car revs on its own?
IAC? I don't believe so since this maintains an idle and makes adjustments when there is a load such as the A/C turning on but I am not positive. How did you troubleshoot it to the idle air circuit? They can get clogged and can be cleaned out. There is also a way to reset of the IAC that can clear up issues too.
#13
Re: car revs on its own?
Not sure how these things work. I brought the car into my mechanic. He said he disconnected the idle control and the car was idling fine after that.
#14
Re: car revs on its own?
Hmm, never tried that. Can someone chime in on the IAC valve going bad? I've had them gunked up before but always managed to clean out the passages and the pintle.
Did you test drive it with the IAC valve disconnected?
Did you test drive it with the IAC valve disconnected?
#15
Re: car revs on its own?
The IAC motor has coils that move the pintle in and out. Shoebox has a test:
http://shbox.com/1/iac2.jpg
.... and a reset procedure:
4th Gen LT1 F-body Tech Articles
The IAC only moves if the PCM tells it to move. There is no feedback to indicate to the PCM what the actual position of the valve is. A data log may show the PCM input that is causing it to reposition the pintle. Unhooking the IAC is just a band-aid to cover up a problem.
http://shbox.com/1/iac2.jpg
.... and a reset procedure:
4th Gen LT1 F-body Tech Articles
The IAC only moves if the PCM tells it to move. There is no feedback to indicate to the PCM what the actual position of the valve is. A data log may show the PCM input that is causing it to reposition the pintle. Unhooking the IAC is just a band-aid to cover up a problem.