sputtering problems at 4000 rpms @ WOT

I have a friend with a 93lx that had an auto in it and it was convertered over to a manual. Anyway he had some problems with getting it to accelerate right. Well he just put a A9S computer in it, it had a A9L. Well this fixed a lot of the problems but it still sputters at 4000 rpms but eventually clears itself up and will go 6 withoug a problem.

if you ease into the throttle it will climb to all the way up the rpm with no trouble or sputtering.

I wasn't sure what to tell him. I though he might try somehting simple like cleaning up the MAF?

Any ideas? Thanks

thanks... I told him to try those three things first...