94 GA SE 2.3L rough idle

Replaced head gasket May '03. Ran ok after reassembly, but slow acceleration from stop. about 30 mph lots of power. vacuum guage on intake says late ignition timing. In park, the engine shakes due to a miss. all vacuum lines in good condition. then it would start and then die when cold. holding down gas pedal helped to start. also after warmed up it was hard to start with very low rpm at idle in park. replaced IAC valve with a junk yard IAC valve for $35. it fixed cold start and die problem. Still misses at Idle in park but now spits and sputters when stepping on gas in park and while driving. Checked plugs and look good. no apparent problems with ignition coils. Any help before taking to mech to reset timing would be much appreciated.

Check your crank position sensor, sounds like it might be bad.