P0402 Fault in 1994 Ford Mustang 3.8L After Head Gasket Repair

Model: 1994 ford Mustang 3.8L Fault Code: P0402 Posted: 2016-12-16 12:45

I own a 1994 Ford Mustang with a 3.8L engine. Recently, I performed a head gasket replacement and reassembled the vehicle. Since then, I've noticed a significant loss of gas pedal responsiveness. The issue occurs after driving approximately half a mile—around 2000 RPMs, the throttle response drops sharply, and only returns when the engine reaches about 1000 RPMs. I have already replaced the throttle position sensor (TPS) and verified that the mass air flow (MAF) sensor is functioning properly. Despite these checks, the problem persists. Does anyone else experience similar symptoms after a head gasket repair? Could this be related to the P0402 diagnostic code or another underlying issue?