: high rpm northstar



ldow
12-22-04, 01:14 PM
I have a 1997 deville and recently the engine for no reason starts to rev high and increase speed. If put into neutral it will rev at about 3250. then it will go back to its normal of about 650. Anyone else have this problem

mcowden
12-22-04, 02:38 PM
That's funny... "for no reason" it revs high. It's revving high for some reason! I'm not trying to poke fun at you, I just thought it was funny.

Anyway, for some reason, air is getting into the intake when it shouldn't be. That could be because of a sticking throttle blade, something holding the throttle cable where it shouldn't be, such as an improperly positioned floor mat, a cruise control cable pulled taut where it shouldn't be, or a problem with the idle speed control (ISC). The throttle body may have accumulated some deposits that are holding up smooth operation of the blade, holding it open momentarily and causing the high RPMs. Throttle bodies need to be cleaned once in a while. It's an easy process to do, and takes a total of about 5-10 minutes start to finish. While you're looking at that, make sure the throttle cables aren't being pulled tight by something broken or out of place. With the engine OFF, you should be able to move the throttle by hand to the open position and it should snap back to closed position quickly when you let it go. If it doesn't, look for something holding it from the point you grabbed it to the blade and rule out the cable. If it does snap shut, look at the cable and the pedal (floor mats out of place holding it?). Does the throttle pedal stick at any point in its travel?

The ISC controls how much air gets to the intake at idle. If it's damaged, bad or the wiring to it is damaged or bad, you can get erratic behavior. 3250 RPMs is pretty high for an ISC problem, but I suppose it's possible. Anyone else care to comment here?

The only other thing I can think of is the backfire valve thingee that Bbob has described in previous posts. Maybe it's stuck or the seal is bad?

Just a few thoughts anyway. Your problem isn't too serious. A little more information and someone will be able to point you in the right direction to get it fixed.

Good luck...

M C
:cheers:

BeelzeBob
12-22-04, 10:37 PM
Sounds like the throttle blade is hanging open or there is a vacuum leak somewhere.

Check the carpet and floormats for interference with the throttle mechanism. Aftermarket mats have a nasty habit of fouling the accelerator pedal and linkage.

Clean the throttle body to make sure no deposits are hanging the blade.

Check the overpressurization protection valve on the front end of the manifold. If you look into the end of the manifold you can see the flapper valve that opens in the event of a manifold overpressurization incident. Spray water from a spray bottle around the valve with the engine idling to see if it affects the idle and/or you can hear it getting sucked in indicating a vacuum leak.

Your engind doesn't have an idle speed control motor...but it does have an idle air control valve.... The RPM sounds high for a sticking IAC but it could be contributing I suppose if it is dirty/malfunctioning.