I made the usual throttle body upgrade for my '93 1.9 liter LX to the '97-'02 type. Since then, I've had a rough idle with the engine surging approximately 300 RPM, up and down. It will sometimes level out for a few seconds @ 750 RPM but then go back to revving up and down. After a few minutes of this, the engine will often die altogether, also often doing it at stops. I've chased all the usual possible vacuum leaks with no improvement. I've pulled my hair out to the point where there's none left. Note, it's also thrown codes of 181 and 186. Please somebody help!