OK went to the gas station in my 91 lx (w/ sc-trim) was running fine. on the way back started running really rough. pulled all the plugs they looked fine. swapped the wires, cap and rotor from my 88 and made no difference. there is no vacuum leak (solid 19" at idle). pulled the FPR vacuum line it changed the idle. unplugged my MAF and it changed the idle by a very very small amount. no check engine light. can anyone tell me whats wrong with it?