well it idles fine with just the start of the key, and then when u give it some throttle and back out it wants to stall, when it starts to stall i can hear the iac open up and then it either sits and high idles or surges. like something is happing when it goes from negitive to positive vacuum

im thinking the engine builder did not replace the o-rings between the intake and plenum, they were for some reason to big to put back in when we had it apart. soooo he said he had to order new ones from merc (not 100% sure he did)

i swapped map sensors between motors and it gave me the same map sensor low code, that means manifold pressure was low right? like maybe a vac leak?

Yes buddy man if u can get a smoke pro it will take all the guess work out. Or start motor and spray down to look for leak. Careful not to start a fire. Or go buy smoke pro then return it when done......haha sorry had to say it they are like 1000.00 man.

cool buddy thanks for all your help, i did talk to dustin at whipple a couple times, he said he has had very little luck with spraying and getting a difference in rpms on a 500 efi motor, but i did try it anyway and didnt find anything, im just going to go home after work today and pull the plenum off and check out the o-rings

Cool best of luck. Just don't like the fact tps volts are hanging up that's not right. Keep pushing u will get it. Some times we look to deep and hard and the problem is right in front of face.

Well I am heading home now from hospital with a new baby girl talk soon!!!
Skydog

Ps how far from north ill are u? I got a smoke machine u can use.

WOW congrats, we just had a baby girl too, well 10 months ago...........damn time flys

Congrats to u too buddy!! That's got to make boat problem that much funner I am sure.......

I'm still thinking vacuum if that makes you feel any better LOL. Don't rule anything out, could be your plenum o-rings, intake to heads, behind the throttle body, etc. It seems the motors trying to make up for unmetered air.