I have a 93 b2600i 4X4 tht has been a great truck for many years. It currently has 69000 miles on it. I was have a problem with the clutch so i replaced the clutch master cylender and that fixed my problem. Afte that I started having a problem with the idle. What happens now is it will start right up but will die after a few minutes. If i push the accelerator all the way to the floor it will rev up to about 3000 then back down to 500, then back up to 3000 and back to 500. It will keep doing this as long as it is pressed all the way in. The only way I can get it to rev any igher is to pump the pedal. does anyone have any suggestions, they would be greatly appreciated. The truck also acts like it is going to back fire sometimes. I don't know if that helps with diagnosing the problem or not.

Thanks

 

If this problem started happening just after you replaced the Master cyl then give a very close check to anything you may have disturbed or accidently unplugged. 99% of the time, if a problem starts up right after some other repair has been made they are related. Believe me as I have done it myself. Pay special attention to the MAF, throttle position sensors as that is what it is sounding like.

 

Sounds like its also a problem related to open/closed loop operation as it dies after a few minutes. I would definatly check the MAF, O2 sensor, and TPS.

 

i would agree on the tps it is messed up inside so it sends good signal then none at all causing it to reve up then drop back down