I just finished switching engines to a 383 rebuilt LT1. The car starts fine, idles fine, but as soon as I start driving the car it can't maintain an idle. As soon as I let off on the gas pedal long enough for the RPMs to go down, it just goes straight to dead. I have no problem being able to start the engine after it dies.

The engine is a rebuilt 383 with stock heads and TB, mostly stock accessories, and a pcmforless.com tuned PCM. Tomorrow when I can work on it again I am going to try switching back to the stock PCM for a run, to see if it is a problem with the tune or the PCM.

Any ideas why it would be unable to idle while underway?

 

have you asked bryan his opinion, he is pretty cool about asking questions like that

i had the opposite problem with my car, when moving it idled at like 1500 rpms, very annoying, i think it had to do with a setting in the pcm for idle while moving or something like that

 

Throttle Follower IAC offset vs. MPH ?

 

Even before looking at the tune... if you can log it as it is doing it... you may see your IAC counts max out at 160. If this is the case, the TB is not open enough to maintain adequate air for idle under load (do you have an A4 or M6).

You may just need to adjust the little screw adjustment on the TB to allow more air in.

If you can log a file... and post it here.... it may be easier to diagnose if this solution or the one from Shoebox doesn't work.

 

Of course. You don't want to do anything before looking at a scan of what is actually going on.