2000 Cavalier rough idle

[Anduril]

I just bought one of these a couple weeks ago, didn't notice it on the test drive at the time, but a couple days later I noticed the car idling rough. A couple days ago I changed out the plugs and wires to try and correct the problem, no difference. The plugs themselves looked great, no fouling, no oil, no deposits, just a little brown.

Looking at the tach, "normal" idle seems to be about 600, though it'll dip down to 500 momentarily then recover immediately. That slight dip is what causes the vibration. Took it to the dealer and they said it's just a characteristic of 4-cylinder engines, I call Bee Ess on that one. Now I'm thinking vacuum leak, but after that I'm all out of ideas. It's a 2.2 OHV with 4-speed auto, 48,000 miles. The car runs smooth during normal driving, only runs rough at idle. There is no CEL and the dealer said everything was "within spec." However, they're closed today so I can't get the car back until Monday.

 

[Colt45ws]

I call - - - - - - on the dip to 500 being normal. Mine idles in the 570-620RPM range. But really, I hardly see it go below 580. Im not sure on this one. IAC possibly.

 

[Anduril]

I know it's not normal, my girlfriend has a '99 Cavalier, same engine as mine. Even with 113k on it and a broken engine mount, it makes a lot of noise at idle but with the hood open it appears smooth. It doesn't visibly shake, and although she has no tach in her car, it does not sound like the revs are dipping and recovering as in my car.

I'm beginning to get - - - - - - off by dealer service departments. The last two times I've brought problems to them (pinging Corolla that was unaffected by premium gas, seafoam, water mist through the intake, and injector cleaner, and now this), they've just read the computer, found no codes, and dismissed it as "normal."

Maybe I should try taking it to an independent shop for diagnosis? As soon as I get the car back I'm checking for any obvious vacuum leaks and the like, but if I don't find anything, anyone know a good mechanic in the Orange County area who might be able to figure this out? I'd most likely be able to do the actual repair myself, I just need someone to tell me what it is I need to fix.

On a side note, the idle would appear to smooth out when I run the A/C.

 

[Merkava_4]

I'm like you, I can change parts all day long, but when it comes to a drivability issue that requires a diagnosis, I have to seek help. The Cavalier will have to be hooked up to a scanner to read all the operating parameters in order see what the computer is seeing for comparison to known good parameters.

Forget about the dealer and start searching for a good independent shop. Tell them that you just want to pay them for a diagnosis and that you plan on changing the required part(s) yourself.

 

[va3ux]

I was just researching this very thing over on j-body.org. My wife's '01 Sunfire (2.2 OHV) has always had a bit of a shaky idle but otherwise runs great. Turns out that this is a pretty common problem with no apparent fix. The guys over on j-body.org have cleaned parts, replaced parts (gaskets, injectors, TPS, IAC, etc), but all to no avail.

 

[punisher]

A vac leak or a leak in the intake between the MAF and the thottle body are the most common causes of idle roughness. If the idle is dipping, ck and clean the IAC and throttle body. Gunk and deposits find their way into both components causing reduced airflow.

It is always nice to have a proper scan tool with a data link for performance problems. Looking at your fuel trims will eliminate a lot of guesswork.

Some engines just idle rough. Different engine mounts, accessory mountings,and even subframe mounts can all contribute to NVH concerns.

 

[CBDFrontier06]

Have you run any fuel injector cleaner thorugh it? If not, run your tank nearly empty, pour in some Chevron Techron, add 10 gallons of gas and drive til empty again. This has cured several of my cars' drivability issues in the past. Could save you some serious diagnostic $$ that bring no concrete answers.

 

[Anduril]

That was the first thing I tried.

punisher: I don't think mounts would cause the revs to dip like that, though.

 

[askani79705]

Fuel filter ?

 

[Anduril]

Wouldn't that affect drivability as well, not just idle?

 

[Oldwolf]

My Cavi has the 2.4L. I switched over to Bosch Platinums and they wore out after about 60k miles. When I went back to the more expensive AC platinum plugs, I was surprised how much better it ran. After the fact research showed that most folks recommended sticking with the AC's. Of course it could have just been the new plugs.

My point is, even though we have different engines, you may want to install the factory recommended AC plugs.

('00 Cav, 2.4L OHC, M1 10W-30, 10K Mile OCI)

 

[askani79705]

Quote:

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Wouldn't that affect drivability as well, not just idle?

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I'm thinking the pressure is higher during driving.Had a similar problem with a Olds 2.2L I thought it might be cheap for you to try out and it needs to be done anyway.