Esprit SE low RPM surging

[stockcar44]

Got an 89 SE that pulls nice and hard above 3000 rpm's but has like a lean miss/misfire just cruising along. I'm thinking vacuum leak but can not find one. It has the S4 upgraded chip in it. When I bought the car it did not do this and it seems to be getting progessively worse. TPS is new as is the computer and IAC motor. Any Esprit ideas? Thanks

Marc