Friend has 2000 502 mpi. He had a blown head gasket and replaced it. Now it surges on idle, backfires and can only get 42-4500 RPM. (prolly not enogh info to work with but it is a start)

It sounds like the rocker arms are to tight and/or valve is hanging open.

ck vacume, sounds like may have a leak, timing set correctly ?

we will check timing tomarrow. How do you bypass the computer to reset the timing?

check the 5 and 7 plug wires. might be crossed.

Take a can of throttle body cleaner or starting fluid spray small amounts around intake to see if you have a good seal. Don't spray too much just a little at a time. If you have a vacuum leak you will know it.

If its stock,, there are not adjustable.

Sounds like he didnt bypass the ECU to time it.