Bean having an issue with my car lately, it will stumble really bad like its misfiring until I get into high rpms, then it drives perfect but when I take the line off of the stock FPR it will drive alot better, but still stumble a bit, and even worse over time. Any help would be appreciated, yes my battery/alternator/fuses/fuel filter/cap/compression and plugs are good. Can't hear or find any leaks in the vaccum lines. its a stock d15.