Hi guys, I have a 1998 GMC Envoy ( or Jimmy, 4.3L 4x4) that started with the RPM's surging erratically, then it began to do it while driving, the vehicle would surge as well with the RPM's. The problem initially started after I replaced the air filter and spark plugs. Now the truck has trouble backing out of the driveway, it seems to have lost all power. After backing out of driveway (a slight incline) and getting on level pavement, the truck struggles to go down the road, does not want to shift, and also seems to be chugging and missing.........I checked voltage on TPS, it is normal....the engine code came on a long time ago and I had it checked and from what I can remember, it had something to do with the evap canister but when I had someone to pull the code a couple weeks ago, the fuse to the cig lighter was blown so the reader could not pull code....does anyone know of a similar problem that would start with engine surging and end with what seems to be a trans problem? I will probably drop the pan and change the filter this weekend....any additional help would be appreciated

 

If you haven't replaced the cap, rotor, and plug wires, I would do that now. These trucks are very particular about their ignition components and prefer AC Delco caps & rotors especially. They also prefer AC Delco or NGK double platinum plugs.

 

oh, that sucks. I put Bosch platinum plugs in when I did the tune-up and I checked the price of the wires and about had a stroke. As a side note I unplugged the Mass air flow sensor and the truck has regained some power...not all, but it can back out of the driveway and it shifts in and out of gear better. Does you know how to test a MAF? I tried an Ohm test and it did not do anything.

 

If you don't have a code for the MAF, the sensor is likely doing its job, but may be hindered by dirt caked onto the elements. The only real way to test it is to monitor its output using a scan tool.

Run through the steps detailed below to clean the sensor and see if that helps:
MAF Sensor Cleaning

To test the wire integrity, grab a spray bottle filled with water. Go out to the truck at night and start it up. Shut off the lights and mist down the wires from the distributor down to the plugs. Look for spark escaping the wires. If you see a light show, you need wires.

Also, if your tune up didn't include the cap & rotor, you probably want to do them as well.

 

I just wanted to update....I had someone put it on a diagnostic and it came up with a trans slip code...took it to a trans shop and they said tranny is ok. It is not the wires, cap, rotor, or plugs, I am going to try fuel filter, and clean injectors. No thunder storm when spraying the wires.....I'll keep ya posted.