1996 mercruiser 5.7 efi tbi stalling at idle

[Cdn20valve]

Since i bought the boat used it has had a high idle 1200+ rpm. recently i had a stall issue develop and i decided to finally fix the idle issue once and for all.
engine will run all day over 1000 rpm. previous owner had drilled out the throttle plate stop screw. (probably trying to lower idle rpm) if I set the idle mechanically at 1000 rpm or higher, it will not stall. however the idle is just way to high to manoeuvre the boat at the dock.

I have a rinda scanner. scanned for codes. had a code for tps . i replaced tps. no change.
i adjusted the tps and stop screw so idle could be at 650 to 750. stalls. as soon as tps voltage goes below .66 at idle. it stalls. .68 or .7 and higher it runs. if tps voltage is in .66 or lower it will start and run for about 3 seconds and stall. i can get it to idle at 800 rpm. but when i turn off and restart it won't start.

i replaced the iac. no change
i've rebuilt the tbi assembly. no change

fuel pressure gauge reading is within spec 32 psi.

i'm at a loss here guys. I've tried everything i can think of. anything else i can do before i throw in the towel?

 

[Bt Doctur]

intake manifold leak, vac leak , throttle body base gasket leak

 

[alldodge]

This is the classic IAC issue, will run above 1000 and will dies below it. The idle plate is set for a specific air gap and then the IAC takes care of the rest. Need to check for a vacuum leak, then test the IAC connections.

 

[Cdn20valve]

This is the classic IAC issue, will run above 1000 and will dies below it. The idle plate is set for a specific air gap and then the IAC takes care of the rest. Need to check for a vacuum leak, then test the IAC

This is the classic IAC issue, will run above 1000 and will dies below it. The idle plate is set for a specific air gap and then the IAC takes care of the rest. Need to check for a vacuum leak, then test the IAC connections.

View attachment 259950

after replacing intake manifold gasket and buying a rinda scan tool and trying to diagnose issue. i finally gave up. i never did solve the issue. i decided to ditch efi and install a carburator. a new edelbrock 1409, new intake manifold, low pressure carter fuel pump, and new distributor. the boat has never ran better. idles at 650 rpm, revs up to 4600 at wot. sounds so much better, and pulls much harder! i wish i did this years ago, instead of nursing a sick efi system. thanks for your replies guys. oh and fuel economy seems the same, no noticeable difference.