2000 175 Ficht won't idle below 1400 RPM

[copano]

175FPLSSV starts good, runs good, just won't idle down TPS in range, no fuel leaks detected, EMM had code 15 ROM checksum, sent EMM to DFI Technologies for repair but high idle persists at a steady 1400-1500 RPM.
I also verified TDC, a timing light indicates 26 BTDC at 1500 RPM, using diagnostic program to set offset had no real effect on idle speed.
What have I over looked?

I should add that there is no bind in the throttle bodies as they are closed or in the TPS. and did a injector disable in the software in an attempt to isolate a leaking injector.

[Nordmann]

Have you checked the lift-pump diaphragm yet?

[SEAHORSE]

What is the TPS voltage at that rpm?

Unless there is a leak of unregulated fuel into the engine such as from the VST or an injector, the TPS is what determines the engine rpm.

[copano]

TPS voltage is 0.49v.

I disconnected the lift pump pulse lines and the VST vent line, squeezed primer, no fuel leakage.

[copano]

Some additional info and an update, when this boat first came in to the shop it started and idled fine, the moment you blipped the throttle it would only idle down to
1500 rpm, same thing after I got the EMM back from DFI, so this afternoon I thought I'd fire it up again, great, idled fine, so I broke out the timing light to verify timing matched
what the EMM was looking for, I then gave it a little throttle and again back to 1500 rpm after return to idle setting.

So, after sitting for a day or two it idles fine on start up, but the moment any throttle is applied it won't idle back down.
Just for giggles I ordered a used TPS to try but it won't be here for a few days...but the TPS checks out fine in software and ohm meter so I'm doubtful it fix the issue.

After a long talk with Chet at DFI we entertained the possibility of corrupted management software in the EMM especially after the code 15 repair.
The software version loaded in this EMM is 9236.
Chet informed me there was a revision with a release note of "Always 650 RPM", he just doesn't know if that was to correct a low idle issue, or to correct a high idle issue.

I just wonder if anyone has seen this issue before, fuel leaks have been ruled out.

[copano]

Update, a different ECU resolved the issue, took awhile to find a good one, the two before were junk throwing fistful of 8 codes.

[DaleH]

Update, a different ECU resolved the issue, took awhile to find a good one, the two before were junk throwing fistful of 8 codes.

Thank you for chiming back in and giving all an update (too many don't .... ) as it sure helps to preserve the integrity of the data, plus helps others, in the future, to search on here!