car revs itself 400-2500rpm

[CT Tim]

Today when I turned the car back on to move it back into the driveway after checking the tire pressure(leaking from both tires on pass. side now), the car started really dipping while idling, it sounded like the car was about to stall, and then it would start reving itself to about 2500, I have to say it is rather strange to see your car reving itself up and there is no one in the driver's seat (I was letting it warm up before I moved it as well as listening to how it is at idle on a flat surface in about 36 degree weather considering I just got this car a couple weeks ago and it is not my daily driver,I've maybe driven it a total of 40 miles since I got it). I haven't had the time yet to take it to any professional and I'm almost afraid of what they will say;but I was wondering if anyone knows what this could possibly be. Keep in mind the car continued to do this for a solid 5 minutes before I decided to get it off the street and put it in the driveway.
Any responses are greatly appreciated-
Thanks-Tim

[billyo69]

I m not sure but i think it could be a bad intake gasket.

[CT Tim]

Thanks for the response. Do you happen to know the difficulty/price range of replacing the intake gasket.
Also I forgot to mention this is a 2000 ls,3.8, w/100k on it.
Thanks-Tim

[billyo69]

I dont think it is that big of a deal.Im sure some one will respond who has had to do one before.Where are you from?

[billyo69]

Also i think while the car is running you can spray some CRC or WD40 around the intake gasket area and if the car revs up that is your problem. Im sure a more knowligable person will correct me if im wrong.

[CT Tim]

Thanks for the response. I will try the wd. By the way I'm in Connecticut,right outside New Haven.
Tim

[billyo69]

I am in Mass just east of worcester.I know a garage up here where they are honest and priced reasonable on work.And you can bring your own parts if you want.

[maxwedge]

If it was the usual upper intake problem you would be loosing coolant get this diagnosed before jumping into the intake manifold issue.

[CT Tim]

Well I haven't driven the car more than 40 miles or so but when I purchased it the coolant reserve was bone dry and the light came on when it was at idle in driveway (coinincidence or because I was parked on steep hill),so I filled with the havoline and it is extremely dirty-one of the first things I intend on doing is taking it to the local Chevy dealer for the $200 flush/fill/replace thermostat.
Do you think they should pick up on the problem during that process? If they do and tell me the problem I think I'll have that taken care of at a local garage that has done work for me previously because I can imagine how much they'd quote me at a dealership.
Thanks for everyone's advice-
Tim

[maxwedge]

Coolant loss in that engine is an issue as with any, have that addressed diagnosed first.

[CT Tim]

So basically you agree that I should go for the coolant flush first and see what they tell me at the dealership after they've done that?
Thanks-Tim

[maxwedge]

You are wasting time, again, doing a coolant flush this does not find/diagnose the coolant loss.

[Pat_OD]

It may be the Idle Air control valve.

[03CavyMan]

Originally Posted by Pat_OD

It may be the Idle Air control valve.

Exactly what my thoughts were.

[wtousand]

This problem could be the idle air valve or, more likely, any other simple vacuum leak. The varying rpm can be caused by a computer seeking correct idle, trying to compensate.

All fuel injected engines act similar during a general manifold vacuum leak (such as a loose vacuum hose). The engine idles fast during start-up because it is set rich during warm-up and can stand a bit more air mix. When the engine warms up, it will likely stall during idle because the engine is set to normally idle ultra-lean after warm-up and more air is too much air ...way too lean.

First check all the vacuum hoses with the engine off. Then listen for a loud hiss under the hood with the engine at fast cold idle. The sound will help guide one to the leak. It usually isn't required, but use a small hose to the ear like a stethascope if necessary to pin-point the source.