rpms

I just wired up the high idle mod for my late '03. Setup is clean and looks good. Recently though, I've had a strange issue happen when the switch is flicked on. The rpms slowly climb to 1200 but "surges" ( not sure if correct term). The rpms quickly jolt down to 1000-1100 briefly then bounce...

Hi everyone - I hope one of you will have a suggestion for me. I have an 03 F250 (automatic) 6.0L. I'm getting an engine vibration when the transmission shifts into the highest gear and I try to maintain my speed or accelerate. It feels like one or two cylinders are not firing properly causing...