The engine revs

Tiny
CLIMBER LINEMAN
  • 2001 GMC JIMMY
  • 98,876 MILES

The motor, after driving a while, throtles up an down at 1500 rpm/55mph? It has been in 3 different shops for about a month and no one can figure it out. Please help, it is driving me crazy. I have changed the egr sensor, evap sensor, all o2 sensors and a new fuel filter.

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Tuesday, November 1st, 2011 AT 11:00 PM

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Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,272 POSTS

Is the fuel pressure within spec? Have they checked for vacuum leaks, the throttle position sensor.? Has the check engine light come on?

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Tuesday, November 1st, 2011 AT 11:35 PM
Tiny
CLIMBER LINEMAN
  • MEMBER

I have changed the throttle position sensor also. No check engine light. Do you think it might be the fuel pump. Why would it do it after driving for 45 mins to an hour? No codes are showing.

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Wednesday, November 2nd, 2011 AT 12:31 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,272 POSTS

It could be the fuel pump. I have seen them get "lazy" is the best way to put it. Some won't start the car, but once running will keep it going. Others will start the car and then not maintain. You can check it yourself. All you need is a fuel pressure gauge. Most parts stores will lend them to you for free. Once you get one, go to our homepage under the DIY section for detailed directions and a video to help.

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Wednesday, November 2nd, 2011 AT 12:53 AM
Tiny
CLIMBER LINEMAN
  • MEMBER

Thanks a lot! I will let you know how it goes. Thanks again,
Richard

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Wednesday, November 2nd, 2011 AT 1:13 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
  • 68,272 POSTS

Glad to help. Let me know what you find.

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Wednesday, November 2nd, 2011 AT 1:21 AM
Tiny
1013BNT
  • MEMBER

Mine waslow on transmission fluid and doing same thing

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Friday, December 9th, 2011 AT 7:22 PM
Tiny
CLIMBER LINEMAN
  • MEMBER

I just had a new transmission put in sept 2010 and havent drove it a lot. Had the fuel pressure checked and is good. Had new pludgs and wires installed. Dont know what to do next?

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Sunday, December 11th, 2011 AT 4:30 PM
Tiny
CLIMBER LINEMAN
  • MEMBER

Checked fuel pressure and is good. Installed new plugs and wires. Had a new transmission installed sept 2010. Dont know what to do next.

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Sunday, December 11th, 2011 AT 4:33 PM
Tiny
SRTRAUB
  • 2000 GMC JIMMY

Thanks for the response. I seem to have not been clear with the A/C. It is an additional issue. Sometimes we start the car with the A/C on and the car does not seem to want to go (car working very hard) and remains that way for a while. Sometimes it goes back to normal (RPMs drop and car responds to the throttle normally) and sometimes it doesn't until we turn off the car and come back later. Sometimes normal. Sometimes not. I agree no trans and A/C connection, but could the A/C switch be causing this other issue?

Last edited by srtraub on Sat Oct 20, 2007 4:54 pm; edited 1 time in total

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Tuesday, August 1st, 2017 AT 10:21 AM (Merged)
Tiny
BLACKOP555
  • EXPERT
  • 10,545 POSTS

Id check the throttle position sensor, it should respond to the throttle no matter what. Scan it for trouble codes.

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Tuesday, August 1st, 2017 AT 10:21 AM (Merged)
Tiny
JESSEB11
  • 2000 GMC JIMMY
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 150,000 MILES

I will be driving my 2000 gmc jimmy and I will be at a constant speed and the rpms will jump and fall. When it does this I can hear and feel the vehicle rev. Has been doing this every time I drive it but not 24/7. Help is greatly appreciated. Thanks

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
  • 28,546 POSTS

If that rpm change is about 200 rpm, not like down-shifting to a lower gear, that is the torque converter unlocking. It will unlock when you let off the accelerator in preparation for coming to a stop, when you tap the brake pedal, and if the engine gets too hot. When it unlocks intermittently for no known reason, it's usually the brake light switch is out of adjustment. Try holding the brake pedal up with your toes. If that stops it from unlocking, check the adjustment or replace the switch.

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
JESSEB11
  • MEMBER

So I tried the hold the brake pedal up with my foot and it was still doing it. I did notice the fluctuation was about 200rpm give or take. What should be my next step. Thanks

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
CARADIODOC
  • EXPERT
  • 28,546 POSTS

Next I would use a scanner to view live data and to read any diagnostic fault codes. A dirty spot on the throttle position sensor can make it appear to the computer as though you're headed for idle or wide-open-throttle, two conditions that will initiate a momentary converter unlock, but if the sensor fails completely, it will set a fault code. A simple glitch in the reading may not set a code but it can lead to the converter unlocking.

Most scanners have a record function that allows you to record a few seconds of data to be reviewed slowly, later. You press the button when the problem occurs, but since the data travels through the scanner's memory, the recording actually starts a couple of seconds before you pressed the button. That will allow you to see what happened when the event occurred. If it works like the Chrysler scanners, you can include switches in the list of recorded data. That means you can add the brake light switch to the list.

If you watch the throttle position sensor's signal voltage, it should remain steady when you hold the accelerator pedal steady. That works best if you have the cruise control on. You'll see very slow and small changes take place. The clue you're looking for is if it suddenly pops from, lets say, 2.86 volts to 3.22 volts, then back again. The throttle won't move that quickly with the cruise control.

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
SHAELENE
  • 2000 GMC JIMMY
  • 17,000 MILES

When I turned on the heater, the engine would rev while driving, even while stopped at a red light. Now I turn on the heat and no warm air out, but the revving issue has stopped. Also, there was a slight odour of antifreeze in the vehicle.

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
RASMATAZ
  • MEMBER

Could be a vacuum leak/actuator in the AC/Heater system-

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
WRENCHTECH
  • EXPERT
  • 20,809 POSTS

The engine speed issue was likely the computer raising the idle because the A/C compressor kicked in which happens in many modes. The smell is pointing to a leaking heater core and the lack of heat could mean it's low on coolant now.

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
SRTRAUB
  • 2000 GMC JIMMY

I have a 2000 GMC Jimmy; we had the tranny replaced with a factory one 9K miles ago and have been experiencing odd downshifting at differerent intervals and the enging seems to be running harder then necessary. Then every once and a while the RPM would shoot from 2000 to 3500 and then back down. Engine sounds matching the RPM so no indication of a tach failure. No leaks of any kind anywhere, did a tune-up and timing was fine. Took the car to the GM Dealer who installed the factory replacement transmission and they found that 3-4 clutches burnt and 2-4 band in rough shape. They obviously replaced all that at no cost. My wife had the car out THE NEXT DAY and it did the same RPM jump from 2000-3500 again!
Occasionally when we have the A/C on, the engine RPMs are significantly higher and the car has difficulty going, but then after a while it just goes back to normal. I had heard a rumor about the A/C switches doing this kind of thing. Could the A/C swith be causing the other RPM/engine issues as well? :)

PS I made a donation :) :D

Thanks for the response. I seem to have not been clear with the A/C. It is an additional issue. Sometimes we start the car with the A/C on and the car does not seem to want to go and remains that way for a while. Sometimes it goes back to normal and sometimes it doesn't until we turn off the car and come back later. Sometimes normal. Sometimes not. I agree no trans and A/C connection, but could the A/C switch be causing this other issue?

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
JACK42
  • MEMBER

The a/c isnt going to make the trans shift funny, just maybe a small power loss due to the drag on the engine. Might want to research another Chevy dealer in your area and have their trans guy have a look. They might honor the other dealers warranty, worth asking if the original guy has already had to go back in

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)
Tiny
CURTISREINERT
  • 2000 GMC JIMMY

2000 GMC Jimmy 6 cyl Four Wheel Drive Automatic 141000 miles

Whenever I'm driving and my rpm's go over 3,000, the engine seems to "stutter." I'm not really sure how to explain it. Once the needle reaches 3000 rpm's the engine doesn't seem to want to go anymore and the rpm's drop down. I just had my vehicle tuned up and for 2 days after that it went above 3,000 without any problems. But, the problem happened again. Why would it be perfectly fine one moment, and the next give me a problem? What should I look for next?

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Tuesday, August 1st, 2017 AT 10:22 AM (Merged)

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