A friend of me changed a 2001 PCM to his 1998 Corvette. Wiring according to factory manuals.

No strange codes, car runs decent, tuning ongoing by me. Everything fine so far.

What bothers me is that when I flash a new version of tune, randomly I lose idle, or actually engine is very hard to start. Originally I thought this is a tuning issue.

So far so good. After a while I noticed that even if I put previous tune back, the car does not start. Then I thought maybe I'm just flushing cylinders with too much fuel.

Now, after several days of experimenting, it seems that after flashing there's no logic when starting goes bad. Just recently, the only chance I made was a rear axle ratio and the result was a hard start. And moments ago the car had no problems to start.

Has anyone had problems like this when switching a PCM from -98 to -01?

I was also wondering, maybe ABS unit, which in this car is in rear, somehow spoils the flashing of PCM randomly?