I have a 2001 GMC Jimmy 4.3, it surges at low speed but when accelerated runs fine. Any idea what the cause might be?

Oxygen sensors shoult be replaced about 65 thousand to 85 thousand miles.

Sounds like 2nd gear in the transmission is slipping. Cars usually shift at 15-20 mph from first to 2nd. First check the trans fluid.

"SURGE" Loses power a little? Common problem is the EGR valve gets a confusing message.It sees many sensor inputs from the ECU and if one of many is sending the wrong message it will open up,falsely. FIND the EGR valve and plug the vacuum source and try the car again. if problem is not there,there should be an investigation by a trained mechanic/technician.


DONT leave it plugged.

Also ,have a transmission expert drive your car so he/she can feel the problem. A tranny shop" won\'t charge you for this test drive.

Depends, You say your fuel pump has been replaced & is working. You do not describe what the "Issue" is. Lack of performance, acceleration ? Is this a situation, where the engine starts & "idles" but, does nothing else?? When you depress the acceleration/gas pedal the car begins to speed up, then abruptly die? If this is your problem, is it a 2.8 V6, 3.6 V6.????? Engine size was also not listed. If it has an abrupt stop when depressing the fuel pedal. Then comes up to speed & stays at speed until taking your foot off: 1.) look for a stuck or "sticking" EGR valve as it is in constant comunication with the ECM, giving instructions to the fuel rail/injector components. 2.) Check the OHM's on the IAC component (Idle Air Control) it is a small oval shaped sensor/control directly on the side of the Throttling body, on both FI (fuel Injected via carburetor,or a MPI Plenum) The other cause, is this has happened is a broken vacuum line at the EGR valve PCV Valve, break in a larger vacuum line such as the one to Power Brake booster.

Check for a vacuum leak around the EGR Valve . It is possible the EGR valve stuck open after cleaning it and causing an internal leak now.

escape 2001 runs rough, but after a certain speed ( 50 mph ) runs smooth.

You may have a clogged up egr valve. When the egr valve gets clogged up with carbon, the truck will run rough, surge stall, and be very anemic on power. Is the service engine soon(check engine) light on? I've dealt with this issue before, and those 4.3 v6's tend to get egr issues. Try this: when it bogs and runs rough, stop truck, open hood, and tap on egr valve base( where it bolts to engine) if rough running clears up, there's your problem. Egr valve is located on front of engine just to the rt of alternator bracket.

You can remove the egr and see if it has been sealing,and if it still moves.

I don't think you have anything wrong, I just don't think you have completed the correct drive cycle yet. Some vehicles must be driven in a very specific way before all the monitors will set. Here is the drive cycle that Gm Recommends:

1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup.
   Do not leave the key in prior to the cold start or the heated oxygen sensor diagnostic may not run.
   
2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire, and - if closed loop is achieved- Fuel Trim.
   
3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
   
4. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
   
5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
   
6. Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
   
7. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
   
8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

Does it sound like a loud winding sound coming from the front right side? I have a 2001 Jimmy and the 4wd tries to engage when driving up steep hills and going at highway speeds. The actuator vacuum switch engaged when the transfer case vacuum switch sends the vacuumed air to the actuator. What is happening is their is either a leak in the vacuum lines, a faulty actuator switch, or a faulty transfer case vacuum switch. When the jimmy has enough air pulling in, the extra vacuum is trying to push the actuator switch in when it is not supposed to. It is a much cheaper fix than a transmission. GMC should have recalled the whole 4wd system on any of the S10's, the JImmy's, and Blazers.