1988 Ranger 2.9L idle goes up when going into reverse

[88 XLT Ranger]

Got a few problems

My 1988 Ford Ranger 2.9LV6 when cold at start up runs at 1400rpm's I slap the throttle it goes down to 1,000rpm's than goes up and down from 1000 to 1300. Once its hot stays around 1000rpm's its an automatic trans I just had the trans re-built last year. When I go to nuteral to clam the RPM's down to 1000 as I shift into reverse it jumps to 1300 and bangs into reverse

I noticed today I started it up it ran to 1400rpm's hit the throttle it came down quick to 800rpm's. Now shifting to reverse the same goes up to 1300 why? is it my TPS or idle Air Control Valve? I hate to mess up the trans with this hard thunk in RPM's going up on shifting into reverse

I always thought it was the trans modulator shift pressure to high

 

[RonD]

The computer controls the idle so there is no adjustment.

Should be about 800-850rpm after warming up.

Check for vacuum leaks, older vacuum lines get brittle and crack where it is not obvious.



Yes TPS could be giving incorrect data to computer, usually you can test these with a Volt or OHM meter.

IAC can be cleaned.

Either with a problem could cause the computer to run idle high

 

[88 XLT Ranger]

The computer controls the idle so there is no adjustment.

Should be about 800-850rpm after warming up.

Check for vacuum leaks, older vacuum lines get brittle and crack where it is not obvious.



Yes TPS could be giving incorrect data to computer, usually you can test these with a Volt or OHM meter.

IAC can be cleaned.

Either with a problem could cause the computer to run idle high

Thanks so much Ron

I appreciate the great info will check the vacuume lines and the TPS