A little backgroung history. I pulled my 575SCI over the winter and installed a set of Brodix heads and a custom roller cam. I dyno'd this engine and tuned it myself with the CMI E-top headers that I run on the boat. My target A/F was 12-1 and I had it almost perfect from idle to 5400rpm on the dyno.
Saturday was my first time on the water with the new combination. I installed my wideband O2 sensors so that I could monitor the engine for the first trip out. The A/F is now reading around 11 throughout the entire operating range(from about 10.8-11.3) The boat runs perfectly except for the goofy unpredictable high idle when cold and there is no longer any soot on my transom.
My question is; Should I take the time tuning to get this thing leaned down a little or just run it? Does anyone have an answer for the high idle problems on these engines? It has done it since new, but I am getting tired of it and I am going to try and correct it.

need to look at the timing at idle,is it high,also,where are the iac's count steps,,may need to physically lower the idle screws and let the iac do its job.other than being in front of the computer,it will be tough t diagnose.hope this helps a little.
did you dyno w/ your boats exhaust on?

Yes, i used the headers and tails off of my boat on the dyno, but I returned the water from the headers to the cooling tower instead of letting it mix with the exhaust.

I rebuilt and dynoed 2 575SCI for a 30 Spectra last year. ECUs had a tune from Mark @ Precision prior. The rev limiter was raised to 5650 I recall. We had blowers rebuilt by Eric @ TBS teflon strips. TBI rebuilt by SPR Performance 217-473-4998. Customer had a prior hi idle to rebuild, it was not present after. Engines were dynoed with my dyno headers with 8 O2 sensors and 1 overall in collector. Engines were installed in boat and O2 checked 11.4-12 under boost. below boost you should be about 13 A/F. I would recal for in your boat operation. I don't believe; by not having water exit exhaust would change your A/F, that much.
I would give Dustin a call. I know he did a excellent job with the tune on a 8.1 that we did a Whipple 3.3. I know we made changes into the 13 A/F below boost and had 12 @ boost.

Mark

A quick option to try, if it is a linear rich condition, would be to lower the fuel pressure a bit.

Yes you should take time to tune it properly. Fuel psi could help if you raised it from stock, but if you have the stock 30psi, I would never go lower because you have far too small injectors for the power potential of the engine.

Verify the engine air temp and coolant temp are similar to what you ran in the boat and dyno. If one is off then your scaling is off. Also verify you are not picking up detonation and adding fuel via the knock fuel....

Thanks for the info. I do not currently have an adjustable fuel pressure regulator, so that is not going to be the quick fix. There is a difference in the water temp from the dyno to the boat. Dyno was 160 and boat runs 135-140deg. I will spend a little more time on the tune. Thanks again.