I was battling a code 34. Then fixed some wiring and now a code 33.
I've set timing per the forum 6deg with the est disconnected.
I've set the TPS to .54volt, replaced the MAF, and checked fuel pressures.
I changed the IAC awhile back (and pulled and cleaned it and the throttle body).
But when I coast below 40mph... the car falls into the twilight zone. It acts like neutral until I rev it to rpm match 3rd gear. But when it's in this no man's land... it idle surges from 800rpm to 2000rpm. Almost like I've got a toggle switch on the ignition power.
if I manually pull the car into 3rd, or just keep my foot on the pedal lightly. It won't do this.
You guys think I might have got a junk IAC?
Or the pickup coil or module is acting up?
Other than that... once it starts and 30 seconds into rough start and the code 33 sets. It runs fine.

 

Can you post an exported log (.csv file) from TunerPro? Virtually impossible to diagnose without it, and can't ignore MAP codes (33/34).

 

I hope you can figure this one out! An 87 5.0 TPI I've been working on is doing the exact same thing on the highway, or faster cruising, but only surging when coasting.