Engine revs up by itself [Archive] - GrandAmGT.com Forum


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08-02-2012, 09:11 PM
This only happens after a long drive on the highway. I put the car into park and let it idle. It revs up from idle about 500 rpm (to 1000 rpm) and then drops back down, continulously.

Any ideas?

Other then that it is running perfect, no issues.

08-03-2012, 04:25 AM
Do you mean 5000 RPM? Throttle Position Sensor, perhaps. Normally you get a DTC code when that happens though.

08-03-2012, 06:18 AM
edited original post. I meant it revs up from idle to 1000 rpm (500 rpm spike) and then back down. I do have an SES light on but I don't think it's related because they did not occour at the same time. Gonna go get the code checked anyways. Just wondering if this was a common problem

08-03-2012, 08:05 AM
It happens sometimes. 600rpm is the stock idle point. It can get down to 500 though if the engine is surging like that. They might not have happened at the same time, but I'd still get that SES light checked and see what code is present, because it could still be related. Surging like that can be caused by a bad MAF sensor, throttle position sensor, idle air control valve, or a vacuum leak. Those are the most common causes at least. The trouble code might point you in the right direction.

08-03-2012, 07:14 PM
This might be related to your problem, cavalier doesn't do that anymore, but when i would drive it, and when i pushed the clutch in, the RPM's went up to about 2,000 and stayed there. As SOON as i came to a COMPLETE stop, they would go back down to 700-1000RPM's. I replaced a few vacuum lines, and it still did it. But after a week, it stopped randomly. Hasn't done it since.

Vacuum leak maybe?

08-03-2012, 07:19 PM
Also, i had a 1996 Cavalier Z24 with a 2.4L LD9 and it did that EXACT same thing. The RPM's bounced from 500-1000, back and forth. And i was told it was an O2 sensor, because if it's bad, it can cause your RPM's to bounce like that. That's what i would say.

08-03-2012, 07:32 PM
No, O2 sensor shouldn't have anything to do with rpm. It only adjusts fuel trims. If it's bad it can make the fuel trims off and make it idle a little rough, but it shouldn't surge. That is usually some related to air, or another sensor on the intake side.

04-30-2013, 09:41 PM
Hey guys....tonight, my '00 GT did this exact thing..... only I did not get an SES light or anything...plus when the RPM dropped down to the 500 point, the headlights & interior lights would dim, like the car was about to die, but then shoot back up to 1000-1100 RPM. Is this the same kinda issue, or something more?

Thanks for any help.