I’ve looked all through this forum and haven’t found a similar problem to the one I’m having.
My car is a 2002 GP GT, mods include 3" downpipe, resonator, no mufflers, and a 9" open cone air filter.
At in town speeds 0-40mph the vehicle behaves normal accelerating through the gears with equal appropriate acceleration. Accelerating to highway speeds 40-75 the car won’t rev past 4000rpms and all acceleration is lost after 3500rpms all while the RPMs continue to rise (but not exceeding 4000rpms) according to throttle position. In order to achieve highway speeds you have to feather the throttle, tricking the computer you want a different gear in order to achieve sufficient speed without high revs and the PCM killing sending fuel into the engine. You can floor it and the engine responds but will rev high without equal acceleration. If the throttle is left open allowing the engine to rev high for more than 15 seconds it will throw the "service engine soon" light on, but then goes off after you let off the throttle.
I was thinking it could be a clogged Cat, the torque converter, abused transmission, or maybe the MAF is bad.
Any insight into the issue would be much appreciated.
Additional symptoms: Terrible gas mileage, and a loud sucking noise coming from my air filter during idle
