Erratic shifting when engine has high idle

[RLJCHEVY]

Greetings, this is my first post so I am not sure if I am in the right place. I have a 1989 K1500 standard cab. 350 TBI. Occasionally my engine will idle higher than normal, say, instead of 800, it will go to 1500. Sometimes at the stoplight it will serge. When the engine is idling high the transmission will shift into high gear and the engine will bog, I can push the accelerator pedal to the floor and the engine will not rev, it just keeps bogging. If I lightly let up on the pedal it will correct for a bit. also when I am on the interstate between 50 mph and above the trans will shift in and out of overdrive or the torque converter is locking and unlocking. As long as the engine is idling correctly the trans shifts fine. Any ideas? Thanks

 

[DerekTheGreat]

Get ye self a scanner, I like the MT2500 brick variants, the one with the graph (MT2500G?) is the better one. But, you'll want to connect it and see what the data says. I'd start by looking at the TPS, O2 and MAP sensor data pids as well as open/closed loop status.

 

[Erik the Awful]

The stoplight surging is likely the torque converter engaging because the engine is over the torque converter's stall speed.

You need to diagnose why your engine is sporadically running fast.

When the engine is idling high the transmission will shift into high gear and the engine will bog, I can push the accelerator pedal to the floor and the engine will not rev, it just keeps bogging. If I lightly let up on the pedal it will correct for a bit.

Your symptoms are hard to understand.
If the engine is idling, does that mean with your foot on the brake?
Transmission shifts into high gear? Do you mean it shifts early?