My 16 FIST suddenly started a mild misfire at idle. Threw three misfire codes. But it went into a weird (to me) limp mode that limited the rpm to 3000 when the car was stationary and I buzzed the throttle...but if I now drive it off it runs full rpm range, full power. Not like any limp mode I've ever seen. It's only in limp mode when the car's not moving. Would that help diagnose the problem?