Well today has been a frustrating day. First off- truck is a 95 GMC Jimmy, 4.3, 2wd, 4L60. It has the lovely OBD 1.5. I'm working on borrowing a scanner that will work with it but wasn't able to get one today.

On about a 20 mile drive today after a few miles the trans stopped locking up in OD. It would shift normally and fine through all gears just wouldn't lock up in 3rd or 4th. After I got where I was going and let it sit a while it did the same thing. Lock up worked fine for a few miles then no more. I've looked up common causes for that and am pretty sure it's just the solenoid or BOO switch. However...

The engine has been sputtering @ idle in gear with the AC on and I was trying to find out what it was while I had some time. The truck had some sort of add on box between the factory harness and TPS sensor. I took that out because there was a short in it and plugged the harness into the sensor. The truck then idled @ about 1800 RPM and wouldn't come down. I checked the voltage to the TPS and it is reading properly. Took off the IAC (idle air control) and it didn't seem to be working very well so I got a new one and put it in. In the instructions it says to "reset" the idle you have to drive the vehicle @ 40 mph @ operating temp and then it should be fine. Did that and all was well. No SES light. Didn't fix the sputtering but it was running and shifting fine except the lock up quit working again. A few hours later went headed out for home. Started the truck up and it went up to 2000 rpm's and didn't come down. SES light came on. I thought maybe the IAC needed to reset again so I drove down the street. The transmission now started holding the vehicle in each gear way too long then it bangs hard into the next gear. It usually won't shift until around 3000 RPM's even with very light throttle. Attempting to manually upshift doesn't matter either. I got home and took out the IAC and made sure everything on it was good- cleaned the contacts again, pushed the pindle in as per the instructions, D/C'd the batt and let the comp reset itself. Went to start it and now it went up to 2800 RPM's and would not come down, tried to drive it to see if it would come down some and it did slightly after a little bit. SES light came back on. The transmission is still not shifting at the right RPM and banging, and now the engine started to all of the sudden drop RPM then shoot right back up to where it was previously. If anyone could shed some light on any of this I would really appreciate it. I've been looking on the forum for about 3 hours and am trying to come up with something. Thanks.

 

Figured it out today. I got the code reader and it was showing the TPS sensor was low. I checked the voltage again on it and it was reading properly- evenly changingin voltage with the amount of throttle given. Went ahead and replaced it anyway and it's fine now. Lock up works and it shifts normally again . Don't know why the TPS sensor tests good but obviously it wasn't.

 

TPS!
Replace it.

 

I already did- that fixed the drivability problems. The truck runs properly now but still sputters periodically with the AC on. It's fine with it off.

 

Have you cleaned the throttle body? Specifically the IAC valve? It may not be able to make the proper fine adjustments.

Have you inspected for vacuum leaks?

 

Yes I cleaned the throttle body and the IAC is new. I couldn't find any vacuum leaks either. The A/C sputter is odd. It almost always only sputters at idle in gear. Once in a while it will in neutral. Drives down the road completely normal with AC on or off. The sputter goes away the second you turn off the AC. High and low pressures are good. Voltage is good.