the engine revs

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

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.

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.

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

Glad to help. Let me know what you find.

mine waslow on transmission fluid and doing same thing

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?

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

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

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

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

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.

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

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.

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.

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

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.

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?

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

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?

Check the PCM ground strap on the cylinder head, some have it at the front, some at the rear, remove the wire and clean the connecting spot and the eyelet of the wire, put it back together and seal with RVT.

While driving on a straightaway in cruise I will notice a feeling that the engine revs just slightly from time to time. The car does not slow or anything but it just feels like the tranny is going into neutral for just a bit then reengaging. When I take it out of cruise it does just fine that I can tell.

have a trasn guy check this it may be the converter clutch is going bad or a fluid change

Auto or Manual trans?

What could cause it to idle at 2000 rpm when first started and stay there?

1800-2000 rpm

Roy

about 1 month ago, my car started to slip out of 1st gear when starting out. I have to double clutch to get it to stay in 1st (works most of the time). Last night, it started to rev in high rpms as soon as I tap the accelorator. I can not get over 10 mph with out it being between 2500 and 3000 rpm. When I shift into 2nd, it will drop to 1500 rpm then immediately jump to 3000 rpm. I attempted to go up a30-40% incline for approx 40ft and could not make it up the incline. The car feels like it is dragging all the time, and I am unable to get over 55-60mph

I dont trust mechanics in my area. How can I figure out what the problem is for sure before taking it to a mechanic

your clutch is slipping and most likely has to be replaced.

Roy

Engine Mechanical problem
1996 GMC Jimmy 6 cyl Four Wheel Drive Automatic 188*** miles

When my jimmy gets to 4500 rpm the headlights dim and battery voltage bottoms out, and I have no idea what could cause this? Thanks for any help

the computer autommatically shuts the fuel off at a certain rpm so you can't drive to fast or to stop damage to the engine.