Yes I'm pretty sure AS&M has it protected...........co-operation only if I buy the scan tool.

Never seen a mefi1 thats locked, I think its so crude there is NO provision for it. The OP has a bad/stuck IAC, vacuum leak or throttle linkage, nothing to do with the programming anyways and like mentioned, mefi 1 shows so little even if he had diagnostic software about the only thing it would tell him is IAC counts are at ZERO since idle is way above target rpm , Smitty

Smitty....Can you tell me (in a general area) where I might find this IAC valve on my AS&M EFI so I can determine if it's bad?....I'm not a wrencher nor a hands on mechanic .....and really appreciate going this route "first" rather than buying a $600 scan tool I might not need.

The TPS is on the side of the TB so look underneath it ? might be a 4 wire plug

THIS THIS THIS!! It is a simple fix and not a tune issue (assuming it worked previously).

Start with the simple stuff as SB first mentioned. Is the throttle linkage allowing the throttle body valve to close all the way? Look for binding, weak return spring etc.

Check for a vacuum leak. Could be a simple hose that came off or a cracked line etc. Bad gasket between the upper and lower half of the intake manifold can leak too, but not likely.
I'd check the IAC last.

#34 on the bottom of the throttle body. Cross reference with a GM part # when you remove.

https://www.mercruiserparts.com/bam/...31336/7595/130

Cross reference #'s
TPS AND IAC cross reference

This what it looks like. Without blindly replacing it or even removing it, IF you find where it is on your TB, pull that adapter and flame arrestor off, start your boat, find the spot where airs hissing in between flange and throttle blades and seal that with your finger tip, if idle drops hard when you do that, its in open position, stuck, dead or bad. Id look at the pcv hose first though as its quite large and make sure its attached and npot cracked. You could also pull the pcv out of lower intake (takes 10 seconds) and hold your finger on end with it idling. Again, if idle changes, you found your problem. You could unplug it completely too , with motor running, put ypour finger tip on the tube it slides over, idle drops, you found your problem, Smitty

If the IAC was stuck fully open could it even raise the RPM to 2500?

if it was truly stuck wide open, i believe it could. When a mefi commands one to 160 max counts or whatever, i dont thinks it anywhere close to being truly retracrted/wide open,Smitty
but, I still bet he has a giant vacuum leak.

Getting cold here going to winterize the boat this is an issue now to take up in the spring ....I found on the r/s rear end of the throttle valve in a recessed hole an alan head screw to manually advance or retard idle
I have one more shot to run engines before winterize ........I'll go through all the steps suggested.........Thanks all!