I don't know if you have it figured out yet, but I have one other idea. Check the fuel pressure. If the vacuum hose is off at either the regulator or the intake it will shoot the pressure up way too high which could be causing some of your problem, especially if you have added an adjustable pressure regulator and have raised it any over stock. ASM should be able to tell you what pressure they want you to run with the programming they gave you. You may also want to check the plugs after a some running just to double check things.

I checked fuel pressure - 43 at idle/ 45 running, as ASM suggested. Talked with ASM today. The two screws control the throttle plates and play a role with the IAC valve. They recommended a diagnostic computer test of the CPU, setting the throttle plates to a 45/50 air count/pulses. They indicated if the screws are too far out of range the IAC would be unable to match counts and that would cause the problem. They also said any of the other things suggested here could cause the problem - got a new vacuum guage will test this weekend.

That pressure seems real high to me. Is that with the vacuum hose on or off? I was originally told by the first person to reprogram my ECU to run that high. Long story short, the program i recieved was not meant for my application. It would load up so bad at idle that it didn't want to run, then when i checked the plugs after a long cruise, they would be snow white from being lean. I ended up just eating the cost of that programmming and sent my ecu to Dustin Whipple where he told me what was wrong with the program that was in it and then reprogrammed it for me. The end result is that I am very satisfied. I only run about 35-36 PSI fuel pressure at idle (with vacuum on) and the new program raised my rpm's by about 300 which is a gain in top speed. When checking the plugs now, they are a nice light tan color as they should be. By the way, this is nothing against ASM or what they are telling you. I have never had them do any programmin for me. I am just explaining what I have been through. Hope you get it figured out.

i have done a ton of dev. work on this motor and still have some in serv. with a ton of trouble free bad ass run'n hours on them...fell free to cantact me by phone...for the next few min i am at 734 458 0924 (ford)
joey
f2-80

ps...some are telling u incorrect info.

I am interested in the correct info. Please share.

Audacity - I'll try calling again your phone's been busy.

Bill 3 - I had the boat out once this year on a long cruise - checked plugs after and they looked fine. Boat idles fine in nuetral, idle problem occurs in gear. Have checked plugs since - still look fine, even after idling in gear and motor cut off (slightly rich not excessive). What size motor are you running ? Factory stock for my 502 is 36 psi with vacuum on. I'm running a 502:
502 30 over (509)
Flat top pistons
Comp Cam 234-237 @ 50 .564/.566 112
Rectangle port heads w/pocket porting
Roller Rocker
EMI thunder exhaust w/long stainless risers
ST 450 mufflers
K&N air filter
Adjustable fuel regulator
ASM programmed ECM, they rec 45 w/vacuum on.

I appreciate all the info, will let it be known when the throttle plates are set and have vacuum checked..

Audacity, Please teach us all, tell us what is correct. Thanks.

bill 3 everything you said was correct

i loved mess'n with these motors...the idle was my largest problem though....finished product..... idled at 710-730rpms no more no less for hours!....it had to sometimes due to location. by the way the cam used way the hell larger than yours.

try this # 734 523 5339

Use a Merc. scan tool to monitor TPS voltage and IAC motor counts. The two set screws are the adjustments. Set the TPS to .66-.70 (about 650-700 rpm) with the primary set screw. Check the IAC counts and make sure they are between 20-40. If they are too low adjust the secondary throttle stop to close the throttle, if too high adjust to open more. Note- the engine must be turned of for 5 seconds and restarted to properly reset the learning of the IAC system.