engine revs on its own

redross006 · #1 11-22-2006, 06:59 PM

Once again i hope someone can help me with this. I drove my car to work today and it seemed to shutter a bit on the highway, But then I parked it for about half an hour. When I started it back up it idled vrey rough and then without touching the gas pedal it revved up to around 3000-3500 rpm's and then slowly(10- 15 sec.) dropped down to regular idle. I shut the car off and then started it back up and it did this again. The car is a 1993 lumina z34 with the 3.4 liter engine. It has new plugs and wires and a new o2 sensor new egr valve new fuel filter and air filter. Pluss the exhaust smell very rich and there is carbon buidup in tail pipe. I also cleanedthe IAC valve. Any advice would help greatly.

maxwedge · #2 11-22-2006, 07:27 PM

Scan for pending codes, look for any obvious vacuum leaks, how old is the T belt? Disconnect the egr for test purposes see what happens.

twistedtech · #3 11-22-2006, 08:27 PM

Does kinnda sound like the IAC might be on its way out.As max stated,scan.

jeffcoslacker · #4 11-22-2006, 08:37 PM

Tps?

redross006 · #5 11-22-2006, 09:01 PM

Quote:

Originally Posted by maxwedge

Scan for pending codes, look for any obvious vacuum leaks, how old is the T belt? Disconnect the egr for test purposes see what happens.

its not throwing any codes

maxwedge · #6 11-23-2006, 09:22 AM

A baseline code reader is not what is needed here, a full scan will reveal possible issues that are ongoing.

Scrapper · #7 11-23-2006, 09:52 AM

have you cleaned the butter fly on throttle body it gets gumed up and wont shut or open right..take some carb cleaner see if it comes out black...

jeffcoslacker · #8 11-23-2006, 10:24 AM

Quote:

Originally Posted by Scrapper

have you cleaned the butter fly on throttle body it gets gumed up and wont shut or open right..take some carb cleaner see if it comes out black...

Couldn't hurt...but if it's not closing completely, they usually stall on cold idle when put in gear, etc...

redross006 · #9 11-23-2006, 11:12 AM

Quote:

Originally Posted by maxwedge

A baseline code reader is not what is needed here, a full scan will reveal possible issues that are ongoing.

Well the check engine light is not coming on yet it does work(i only say this because it comes on momentarily when key is turned on)but my brother-in-law is a mechanic and he says that a scan is not turning anything up when he scanned it at his shop. Do you think this could mean that maybe the ECM is bad?

tblake · #10 11-23-2006, 11:23 AM

have your brother hook it up to a scan tool. Takea look at the long term and short term fuel trip, and also tps voltage/percent, O2 cross counts, and IAC counts, and report back.

jeffcoslacker · #11 11-23-2006, 11:36 AM

Quote:

Originally Posted by redross006

Well the check engine light is not coming on yet it does work(i only say this because it comes on momentarily when key is turned on)but my brother-in-law is a mechanic and he says that a scan is not turning anything up when he scanned it at his shop. Do you think this could mean that maybe the ECM is bad?

He's talking about scanning (to watch the data flow in real time), not code scanning, which is just a record of a fault...

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