I've seen before where the IAC sensor gets dirty. The IAC sensor is located on the top of the throttle body. If you refer to the throttle body as a clock, and picture the egde closest to the front bumper is 6 o'clock then the IAC sensor would be located at 12 o'clock. I think in a 02 GC it should have vaccum lines attached to it, and it's held down by couple of phillp's head screws. (I think) Take it off and clean it with throttle body cleaner until all the black gunk is out of it.
If you are not sure where the throttle body is, find the air filter box under the hood located on the driver's side lower corner. There will be a plastic "tube" going from that box to the top of the engine. Take this tube off and any part that connects to the top of the engine. You will then see the throttle body. It would also be beneficial to clean the throttle body out as well. (It only take a minute and it can only help your gas miliage.) You can find throttle body cleaner at any auto parts store, or Walmart or Target. Let me know if this helps, thanks!
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There could be several issues that could cause your GMC Envoy's transmission to not shift gears properly and the RPMs to rev high. Here are a few potential problems that you may want to consider:
Low transmission fluid: If the transmission fluid is low, it could cause problems with the shifting mechanism. You'll want to check the transmission fluid level and add more if needed.
Faulty shift solenoid: The shift solenoid is responsible for directing transmission fluid to the appropriate gear. If the solenoid is faulty, it could cause shifting problems.
Worn transmission bands or gears: If the transmission bands or gears are worn, it could cause the transmission to not shift properly and the RPMs to rev high.
Clogged transmission filter: A clogged transmission filter can restrict the flow of transmission fluid, causing shifting issues.
Faulty transmission control module (TCM): The TCM is responsible for controlling the transmission. If it's not functioning properly, it could cause shifting problems.
I would recommend having a mechanic diagnose and fix the problem for you. It's important to address transmission issues promptly, as they can lead to further damage if left unchecked.
If you hit the Rev Limiter on a Ford, it will simply bounce the rev back down, to protect the Engine. So, no high Revs. But, you should be able to bring it slowly to a High RPM. That is normal. If there are no Check Engine Light on. You are most likely hitting the rev Limit and need to stop.
Have it looked at by a dealer,iam not sure here but i think you have a vacumn leak like the feed pipe to the servo split but really you need a mechanic who works on these cars day in day out and they will go straight too the problem for you
driving in over drive mode actually is what gives the economy as the engine rpms will be around 300 less than direct drive . Lower rpms = fuel savings
OD should come in around 60 klm/hr and drop out at around 50 klm/hr. When you are accelerating hold the pedal in a set position and watch the rev counter (rpms ) and each gear change you will see the rpms drop and then build back up as the vehicle speed increases At 100klm/hr the revs should be around 3200 rpms or less but if over ( say 3500 rpms) then may be the OD is not coming in. One way to test a box operation is to find a speed shop with a dynomometer and test the gear selections against loads and engine rpms
You could have a clogged fuel filter, if you haven't changed it in awhile. You could have a leak in the intake system somwhere also. When you slow down, you get less power to the engine. It may need spark plugs and wires as well, if in need for a tune up.
I had the exact same problem on my 04 GC. I put some Techron Concentrate Plus Fuel System Cleaner in from Wal-Mart and it seemed to fix the problems right away. Let me know.
being a fuel injected engine , there are many reasons this could be happening. from the top , lets check the Manifold Absolute Pressure (M.A.P.) sensor , as it is easiest. Find the MAP sensor , it has a couple a wires and a vacuum tube going to it and is on the firewall or fender support under the bonnet. Disconnect the wire harness from it (small plug with wires). If the engines RPMs drop to normal , replace the MAP sensor.
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