My daughters 1996 chevy cavalier's engine is surging at rpms over 1500, give or take. Runs fine from idle to 1500, then surges at rpm's over that. She told me it was hard to start the other day. When in nutral, it runs fine from idle to 1500, then surges above that. At full throttle, it surges from full throttle to about 1000 rpm. I work on diesel engines and don't have the test eqipment for this car, can you tell me where to look?
Look for a vacuum leak (lines and intake), Is the engine light on, were any codes present? A faulty EGR or IAC could cause the problem too. Check the throttle cable for any restrictions.
Hey man, thanks for the suggestions. You made my 1500+rpm surge a quick diagnosis to the EGR system. I'm not sure if it's too early/strong a signal to the valve or if perhaps someone (who has messed a lot of other things up under this hood) put the wrong EGR valve/orifice in. When I disconnect the valve the surge disappears. It's an '87 Cavalier 2.0 and thanks to you my nephew will be attempting to pass emmissions as soon as he installs the new EGR valve (provided it's calibrated properly and vacuum signal is ok).
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SOURCE: 1989 honda prelude. engine surges. from normal to 2100 rpms
There is a warm up valve on the throttle body(should have 2 small coolant hoses). remove the valve and have someone start the car while you block the port to the valve on the intake. If that clears up the problem you can cut a piece of cardboard to mount in between the valve and intake.should straighten it out.
SOURCE: dodge ram 1500 engine rpms surge at freeway speed
those sensors could cause the issue, clean the MAF 1st, also clean the idle system using the following procedure, the IAC can cause cruise surge. I use this to cure these problems all the time.
Here is the most common cause of surges and stalls and low idle, it is the idle speed control air-bypass valve (IAC) and throttle valve, they get full of gunk over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.
SOURCE: 1990 Toyota Celica GTS. Idle races too high
sound very much like a vacuum leak.... also maybe your timing is off? possibly advanced? try retarding it with the distributor if thats the case...
SOURCE: 2004 hyundai elantra that surges violently 1000 rpm to 4000 rpm
could be afew things. vacuum leak, one dud HT lead, could be the water temperature sensor, O2 sensor, best to get it checked and get it read for fault codes
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