01 GT40 surging at idle when cold

[Fast351]

Topic says it all. It'll surge (although not all the time) at cold idle dropping to around 500 RPM before recovering and overshooting to 1200 RPM, on probably a 2 second cycle. After a couple minutes the engine calms down and behaves as normal.

I've been living with it for a year because it doesn't really seem to affect it, but it does kind of make the boat a pain to back off the lift.

Back in the racing days when I played with 5 liter Mustangs, which have basically the same fuel injection system, the IAC (Idle Air Controller) was usually the culprit. Some people cleaned them, but at the end of the day most people ended up replacing them.

What is this problem usually on a boat?

[charlesml3]

My 1999 Air Nautique did that for years. It would surge until it got warmed up a bit. I'd usually start it and let it idle in the lift for a minute before I backed it out. I do know it improved quite a bit after a did a full ignition tune-up. Cap, rotor, plug wires, and plugs.

-Charles

[Fgroce]

It will be the same thing as your Mustang, Most likely throttle position sensor or IAC is dirty and needs cleaning. Try the cheap things first.