'01 Pontiac Montana revs high

[Sergeant Slabber]

Ocassionally while in park or driving along, our Montana minivan will increase about 1,000 rpms. It stays that way for awhile and then will idle back down. It will just go back and forth like that. Just wondering what might be the cause of this fluctuation? Thanks for the help!

[BIG DS]

That's a tough one to field. Could be a vacuum leak, a bad idle air control motor, a coolant temp sensor with an intermittent problem, a weak injector.....That one will require a scan tool and some drive time.

[Jeremy airjer W]

3.1 or 3.4 liter? How many miles on it? Does it see a lot of short trips? Does it get onto the freeway frequently? Do you ever notice the RPM's drop pretty low right before they go up? does it do it when its cold, when its hot, or anytime just out of the blue? Does it do it more or less with the a/c - defrost on? Do you ever notice a sticky gas pedal when you initially step on it?

[Sergeant Slabber]

airjer~ I believe it's the 3.4 with around 78,000 in it. It does see alot of 10-20 mile trips per week. The wife says she notices that it runs high when she first starts it, around 2,000 rpms. Normally it would be about 1,100 when first started. It doesn't drop any rpms before it shoots up. As far as a pattern, it seems to just increase those rpms out of the blue. She hasn't noticed the pedal being sticky either. In the spring we had the intake manifold gasket replaced, and early summer we had the A/C condenser replaced. It ran fine after those jobs, but maybe that has something to do with it now? I just added a can of Seafoam to the tank this morning to see if that will help with anything. Any thoughts? Thanks!!

[Jeremy airjer W]

HMMMMMMM! Without seeing it I would hate to even speculate at what it could be. The first thought might be a vacuum leak. Possibly the injector o-rings. I have started to replace these when I do the intake gaskets because I have seen several leak after the job is complete. Also look closely at the plastic/rubber vacuum hoses that go to/from the top of the throttle body. Especially the elbow that goes to the PCV valve, I have seen many of these rotted cracked and leaking!!

Hope that helps.

[Dan Thiem]

What if he sprays some carb spray around under the hood in certain areas while the engines running to see if the r.p.m.s climb up. Does anybody still try that old trick anymore?

[Jeremy airjer W]

Yeaahh, NO! Hears a funny story. I had a Dodge van with a funky drivability problem. I had the doghouse off, was sitting in the drivers seat (by the way the drivers door didn't open) and was spraying carb spray to see if I could find a vacuum leak. So I finally figure out that the EGR diaghram is leaking by this time the engine is at full operating temp. I gave the EGR one more shot to confirm and WOOF!!! The whole thing caught on fire. I'm Stuck in the drivers seat the engines on fire and I have no where to go. I'm yelling for help and finally get the fire out after I burnt my arm and singed some hair on my head.

We know require that the drivers door be functional for any test drive or driveability diagnostics and the shop now has a pretty nice smoker which I have grown fond of!!!!

So, yes it can be done. People do it all the time. I don't recommend it. Please be extremely carefull if you do!!

[Sergeant Slabber]

Thanks for your input guys. I'll look around and see if I can find anything loose, especially that darn PCV which I know can rot or not be seated tightly. I know that sometimes when your driving along around 30mph and you can tell she's running a little high, you can take your foot off the gas and it will hold steady at 30-35 mph for awhile before it idles back down. Nice cruise control!

[Sergeant Slabber]

Airjer~ I noticed after driving the van a couple days ago that it definetly seems to run at higher RPM's when the heater is going. When I shut it off I see that it drops about 2-300. Any ideas?

[Jeremy airjer W]

Anytime the A/c is on the engine Idle will bump up. Usually it will only do it right before the compressor kicks in then idle down after it kicks out.

[Sergeant Slabber]

Thanks! I'll just keep an eye on it for now. At least I was able to put on new rotors and pads before this awesome, ice-making frigid air moved in