Very rough idle and high idle

CBELL23

MEMBER
2001 PLYMOUTH NEON
150,000 MILES

I start the car, the car revs all the way up to red line for a second, then goes back to normal. The idle is VERY rough, almost sounds like a misfire. If I just tap the throttle, the engine revs all the way back up to red line. I checked the throttle body and it has full range of motion and does not stick at all. The gas pedal is not stuck. I just replaced the cam shaft sensor. I was driving the car earlier when it started to do this. If I put the car in neutral, it reved to redline. Please help, I'm lost. Thanks, Chris

4 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Chris:
Check for vacuum leaks, check the idle air control valve, and check the throttle position sensor. If the check engine light is on, have the computer scanned for trouble codes. Most parts stores will do it for free.

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Sunday, September 25th, 2011 AT 3:44 AM

RIVERMIKERAT

MECHANIC
6,110 POSTS

It sounds like the return spring on the throttle body is either stretched, weakened, or broken.

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Sunday, September 25th, 2011 AT 3:44 AM

CBELL23

MEMBER
2 POSTS

Thanks guys, I'm going to get out there and check those. I've pretty much eleminated vacuum leaks, I did find one and fixed it. The engine light is not on. It was on earlier today but I ran a diagnostic and the only code that came up was for the cam shaft sensor and I replaced it. If your suggestions do not fix the problem, I will reply back, Thanks again, Chris.

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Sunday, September 25th, 2011 AT 3:51 AM

RIVERMIKERAT