K8 GSXR idle issues.

A friend just put a new built K8 motor in his car (harness/ECU/tune by Moon), and is having idle issues with the car. Intermittently when warming up when it gets to 180 throws a C40 code (ISC) and dies. Also intermittently will die after blipping the throttle when warm. The ISC has been disabled (physically and in the tune). Moon and others have spent several hours looking for the cause and still haven't found it. Have checked all vacuum lines and fittings for leaks and haven't found anything yet.

Searching the internet, I found some statements that the ECU doesn't like the idle being above 2000 with the ISC disabled and will throw the code if it is too high. The idle screw is backed out completely, and it still idles right around the 2K mark after it warms up. If the low speed idle screw is turned in to the point that it just touches the cam, the idle jumps up to around 4K immediately and the idle gets real funky (dies, etc).

Have been told that the computer controls the idle on these engines, but haven't figured out exactly how. Do we need a Suzuki diagnostic tool to lower the idle?

Anyone have any ideas of things to look for?

Thanks,
Kenton

The idle Air Control is built into the standard throttle bodies, and I see no reason to disable that. I have successfully run the K8 engine with a MoTeC M1 ECU and utilize the Idle Air Control valve, as well as ignition timing to control the idle speed.

If you can't make the engine idle as low as you want (if Greg Moon can flash the ECU, he can change the target idle speed), and you don't have any manifold leaks, then you should consider reducing the ignition timing above and around the desired idle speed.

What manifold pressure are you seeing at idle?