I have a 2.2L autmatic 2001 sunfire SLX and for the past few months the RPM hand seems to be bouncing, it seems to happen every now and then if im driving and take my foot of the gas to coast for a bit and if i put the car into neutral to coast it happens all the time, but a few months ago it never used to do this so i know that something has happened to the car but i have no idea where to start to fix this one. also on only 1 occasion every time the rpm hand would bounce the headlights would go dimmer. but like i said this only happened once. any body got any suggestions as to what could be the cause of this.

the rpm gauge bounces or the actual rpm bounces (like revving)?

Both, the gague itself bounces from like 1000 rpm to about 2500 rpm and the car itself is reving you can really hear it with the louder exhaust i have on the car

It sounds like it could be the alternator. Take it to a shop and have them scan it.

But wouldn't a bad alternator cause other symptoms, and to be on the way out now for multiple months doesn't seem right to me

Sounds to me like it's a vacuum leak. My buddies civic would rev from 1000 to 2500 or so repeatedly at idle and sometimes while driving. Turns out one of his injector seals went bad and was causing a leak. See if you can hear any hissing sounds when the engine is running.

Like he said, there might be a leak. take a can of carb cleaner or break klean and spay a little around the intake, injectors, throttle body, and any where your hear a leak sound, the carb cleaners acts like fuel and it will either dog down your engine or make it rev up a bit.

im deffiently going to try and listen for some hissing sounds tomorrow once the snow stops. hopefully that is the problem it would be nice to see what it is, and hopefully it aint that much to fix

Ha yah mine does that too, It would bounce in a coast from like 400-1500 untill i put it in drive then fine.

Mine also does this but to a much lesser extent. Mine just bounces a little bit, like 1-200 rpms when I rev and let off in park or in motion. I think it goes down below normal idle speed and then is corrected or something.

Damn that's annoying!!

well this helps i heir a small hiss under myhood and my rpms are jumped a bit an now its idlen around 1100 1200 not 900 like it should

its not a leak, buy a 3 dollar car of mass airflow sensor cleaner it does the trick. This happens to GM vechicles, with my brother 4.3 l S10 it throws a check engine light. just take the mass airflow sensor out spray it for 3 or 4 seconds and you idel lower and get better gas milage.

UPDATE: the car is not bouncing as much now it bounces from 500 rpm to about 1200rpm and it is doing that more frequently, lisstened for a hiss also and i never heard anything, but then again with the ractive muffler on the car idle's too loud to hear a hiss anyway