Idle Speed Increases when Engine Is Warm

[Tailwind]

I've got a 1.3L Triumph Spitfire engine running with MS-II, V3 and Ford EDIS ignition. This setup has been running very well for a couple of years now. It starts well, both hot and cold, has no hesitations on addition of throttle, and even delivers reasonable gas mileage.

My question is this: When the car starts cold or 'cool' ( after sitting a bit after a run) the idle is about 8-900 rpm. If the engine is thoroughly warm, the idle is 12-1300 rpm. I am really at a loss to determine why this is so, or what to do about it. Admittedly, the car also did this when it was running with carbs, although the rpm was often 1500 or so.

The problem seems related to temperature, but beyond that I am stumped. I've attached a copy of my latest tune. Also, the air intake is located inside the engine bay, about 10 inches or so behind the radiator. This will result in higher IAT, so is this a likely culprit?

Thanks in advance for any suggestions.

Bill B

[DonTZ125]

Perhaps reduce the IACV duty? Carb'd vehicles idle higher warm vs cold; that's why you set your idle on a warm engine. That's also why EFI vehicles have IACVs that add air to a cold engine, then close as the engine warms up.

[Tailwind]

Thanks for the suggestion DonTZ125:

Right now, I've got the IAC set to shut down at 160 deg F. (I use the Ford PWM with 100% being "off".) I can set this to close earlier and probably increase the WUE to compensate a bit if necessary.

I am a bit puzzled though since the engine is warmer than 160 deg when I notice the "problem". I would think that the IAC is closed at that point. Still, it's something to try.

Thanks, again.

Bill