Strange reving

gluestick · 09-12-2001, 04:29 PM

I have been having an occasional problem with the engine dieseling for a few seconds after i turn it off. Then when i start it back up, only after the times it diesels, it takes longer to start, but always starts. Well today it dieseled again after i turned it off, but when i turned it back on, the RPM's keep reving up and down from 1,000 to about 1,700, over and over again every few seconds. The throttle cable is not moving when it revs, and i can hold it at a higher RPM with my foot on the gas. right now its sitting at my friend's house. Any ideas???

adrial · adrial's Garage

According to the Haynes manual, causes for dieseling is either a "Digital Engine Electronics (DEE) system fault" or "Excessive engine operating temperature"

I would lean towards the DEE.

"The DEE system consists of a control unit and information sensors (notable the oxygen sensor in the exhaust system) which monitor various functions of the engine and send data back to the control unit. The control unit in turn sends out signals to the ignition and fuel injection systems in accordance with driving conditions."

The list of things to be checked/replaced includes:
Air flow sensor
Throttle switch (TPS)
engine temp sensor
fuel injectors
auxiliary air regulator
pressure regulator and damper

To test the TPS, move the throttle off idle (by hand with the engine off is best), then return it to idle. When it returns to idle you should hear/feel a click. If you don't, then you may have found the problem.
I believe the auxuliary air regulator that it talks about is the idle stabilizer, this is located under the intake manifold. To test this just tap it with a screwdriver or something, it tends to get stuck due to carbo deposists. This would need to be replaced, although some have cleaned it with some sucess.

Good luck!

mike944 · 09-12-2001, 05:15 PM

You might possibly have a leaky injector. For a car to diesel, it NEEDS fuel. When you turn the car off, the DME (DEE) shuts off the injectors. There should be NO fuel pulled into the engine after the injectors shut off. Unless, of course, one or more is leaking fuel into the engine.

The other possibility, as adrial said, something maybe wrong with your DME, maybe it's not shutting off the injectors like it's supposed to. OR, Maybe there is power leaking into the DME through some other circuit which keeps the injectors running. Is there any hack wiring in the car? aftermarket radio/stereo equipment possibly? Something could be wired wrong.

gluestick · 09-12-2001, 05:30 PM

The previous owner had an amp hooked up in the left rear wheel well, but he took it out before he sold it. So those wires are not connected to anything at the moment. thats all i can think of for now.

However right now i can't even drive the car due to it reving up and down. So these two things are probably related then?

Thanks for all the info!

[This message has been edited by gluestick (edited 09-12-2001).]

mike944 · 09-12-2001, 06:12 PM

I would think that the revving, and dieseling are related, but it's hard to tell.

Mike

gluestick · 09-12-2001, 06:55 PM

Update: Ok i went back to my friends house and checked it out again. The throttle switch clicks when returning to idle, but the car still doing the same thing. Then i looked around for anything loose or something obvious. The only thing i found was the small fan belt in the front left side seemed to be a little loose and melting. After i pulled on it a little, the car started up again and sounded normal. When i drove it home, however, felt a little weak. Probably a coincidence? or possibly related? Im pretty new to cars, so you'll have to forgive me. My father's mechanic at work does all the repairing, he's excellent and very cheap, without him i would be too poor to have this car =).

[This message has been edited by gluestick (edited 09-12-2001).]

Ven · 09-13-2001, 01:48 AM

Another thought on your problem. When I got my 944 I tried to run 85 octane but the damn thing ran backwards every other time I cut it off. Ran 93 in it, only ran backwards every now and then. started running cheap octane booster with 93 and killed the problem completly.

Cebu · 09-13-2001, 08:27 AM

85.5 944na Tried 87 Octane for a couple of tank full, had dieseling problem and delay firing up on starts also stumbling (flux) idle on start. Added octane booster and cured the problem. Went back to 96 Octane, no more problem.

gluestick · 09-13-2001, 09:08 AM

I have been using 91 octane, the highest i can see offered around here =( . But i will try using an octane booster to see if it helps. Thanks again for all the tips.