[Vandal]

Uncontrollable RPMs

I was just driving down the freeway at about 70 mph when my 2002 1.8T Passat manual suddenly began to uncontrollably rev up its RPMs to about 6500 before I killed it and coasted to the side. I tried to start it again and the same thing happened. I coasted for a safe area, shut everything off, punched on the accelerator and clutch and it started with no problems. I drove it home without a problem either. What could have caused this? It's not like the whole car sped up. Could this be a slipping clutch? Thanks.


Modified by Vandal at 7:06 AM 3-15-2006

 

[2003_Passat_1.8T]

Re: Weird Problem (Vandal)

Hold on, was the clutch disengaged when it ran up to 6500?

 

[Vandal]

Re: Weird Problem (2003_Passat_1.8T)

It seemed that way because the car didn't just take off uncontrollably. The RPMs just jumped on me all of a sudden. Only time I've ever had that happen was in a 1983 Honda Accord that had some after-market cruise control added. If you pressed the clutch while the cruise control was on the RPMs would take off. That wasn't the case here.

 

[spitpilot]

Re: Weird Problem (Vandal)

Still not clear if car itself sped up uncontrollably or engine just reved up but car stayed at same speed...if car sped up with no input from your right foot on gas pedal...I'd suspect the drive by wire throttle system has a (dangerous) fault! If only the engine sped up but car stayed at same speed...clutch slip...but slip would happen all the time under similar conditions of load and throttle opening...ie. every time you wound out in 2nd gear and really got the engine pulling at say 5000 rpms, clutch would slip and revs shoot up to 6500, it would not come and go. A fault in the drive by wire system could come and go...bad connection or fault in circuit board that isn't constant etc.

 

[98passat21]

Re: Weird Problem (Vandal)

Sounds to me like pressure plate failure.

 

[Dave Weitzenhof]

Re: Weird Problem (98passat21)

This also sounds to me like a bad clutch. Did you have the cruise control on when this first happened? If so, the cruise control would apply more throttle to maintain the speed up an incline, and if the clutch were slipping, the revs would naturally go up uncontrollably.
The thing that is confusing me, though, is what it did when you tried the first time to restart it, and it revved up. Did it do that with no pressure on the throttle pedal? If it did that's not the fault of the clutch. Maybe there is something wrong with the throttle function, but that doesn't explain revs increasing independent of the speed.
Think very carefully about exactly what it did and what YOU did at the time, and try to describe it all precisely so we can help you better.



Modified by Dave Weitzenhof at 1:18 PM 3-15-2006

 

[Vandal]

Re: Weird Problem (Dave Weitzenhof)

Thanks for the help guys. Just to be clear -- the engine revved up without an increase in car speed and the crusie control was off. The car acted as if cruise control was on and the clutch was depressed. The first restart attempt saw the RPMs race up again, without any apparent pressure on the gas pedal. I drove it this morning for about 35 miles at varying speeds and there was no problem.

 

[Dave Weitzenhof]

Re: Weird Problem (Vandal)

HMMMMMMMMM.....

1. If the clutch is working properly (not slipping) there is no way for the revs to go up w/o speed increasing.
2. If the revs went up by themselves on start-up (in neutral, I presume), that has absolutely nothing to do with the clutch.
3. Clutch problems are not usually intermittent, so that's very puzzling.
Therefore, are you sure that you did not instinctively push in the clutch (or have your foot resting on the clutch pedal) in the first incident when the revs (and speed) began to increase? If you did, then it simply becomes some sort of throttle malfunction. and things make a lot more sense.


Modified by Dave Weitzenhof at 6:18 PM 3-15-2006

 

[Vandal]

Re: Weird Problem (Dave Weitzenhof)

It most definitely could have been an instinctual thing. The more I replay the moment, the more I think it could have been a stuck throttle and I pushed in the clutch while braking, as normal, but then it revved up. No problems today. I'm hoping the dumbest thing of all happened -- the pedal got stuck underneath the floor mat.

 

[ctobio]

Re: Weird Problem (Vandal)

Do make sure there's no obstructions around the pedal.
You'd be amazed how many fatal accidents are caused by debris lodging beneath a pedal.

 

[MMMH2O]

Re: Weird Problem (ctobio)

I'm wondering..did the display RPM's go up on the tachometer, with no increase in engine speed? Was this a display problem? I have had the speedometer increase with no real speed increase on a Taurus a couple of times. Or did the engine actually increase its output and increase the RPM's?

 

[Vandal]

Re: Weird Problem (MMMH2O)

Thanks again for the replies. I'm pretty sure the RPMs revved up and it was not just a display problem. I'm going to toss out my floor mat; it's the cheap one that came stock and its anchor holes are shredded. I'll keep an eye out for other things and have my shop do a thorough check next week.