90HP Mercury 4Stroke EFI Stalling and Surging

[allnencore]

Hello Fellow Boaters

I have 2019 90Hp Mercury 4stroke EFI its also a command thrust. Serial # 2B566524

Let me start by saying I have read some great in-depth responses on this board so thank in advance for any input.

Well out of the gate I think I have 2 separate problems just based on what I am seeing but we will see.

Issue #1 Engine refuses to idle without stalling. Even upon initial startup or at least within 30 seconds there of. And then stalls. After warm it wont stay running at idle out of gear or just in gear without throttle up.

Issue #2 I can be driving the boat like yesterday a full hour into a trip running 4000 rpms and it randomly started to surge. Oddly, I watched the tachometer while this was happening it never moved. Stopped for 15 minutes to take a swim and headed back to the marina for 1 hour at 4000 rpms and no surging on the way back.

Work I have done thus far to try to fix these problems.

New IAC valve
New ECM
New Plugs
Drained fuel and started new with fresh fuel
New Fuel Filter

Also when I hooked it to the scanner there were no error codes - full disclosure the scanner was a recent purchase and I know very little about how to use it but in the "read codes" feature there were none available.

So as you can see Iv tried a few things to no success.

OK gang fire away! And Thanks.

[EuropeanAM]

What part number IAC did you install?

WHY did you replace the PCM?

[allnencore]

Do not know the part number, it was whatever the mercury dealer parts counter handed me. I will look to see as soon as I have access to the boat. Probably about a week.

So the PCM.... I bought the boat as a salvage... It was at the local marina which was hit by a tornado and the boat was submerged for 2 days under the dock. To add insult to injury it was taken to a local boat place where it sat for 2 months til I got it.

I pulled the plugs and all pistons were dry. Some water in crank case so oil change. The only actual problem I could find that was keeping it from starting was was a blown fuse in the starting circuit.

At that point I have just taken the approach the I am systematically going to change Electro Mechanical parts since I don't want a failure on the water. Hence the PCM. Just for grins changed the starter, PCM, oil and filter twice after I ran it. Put it on the scanner and not throwing any codes.

The Idle Air Control Valve came later in the process as a means to eliminate rough idle and it also fell into things to change as a preventative measure. Also replaced plugs while chasing the idle issue.

Boat runs good once you get it in gear and get moving... At idle, or lack their of its a struggle.

Thanks for the input.

PS Is there a problem with the IACVs by part number?

[EuropeanAM]

There were some faulty IAC's out there, and it's not impossible that you got one of them as a replacement part.

[allnencore]

well holy smokes - will get the part number as soon as I can. Is there some sort of technical bulletin for certain serial numbers?

[EuropeanAM]

Service Bulletin 2021-04(R2) covers sticking IAC Valves.

See if you can get a picture of the IAC valve tag from your engine. Date codes are one of the items to check.

[allnencore]

sorry for the slow response i am out of town.

Will get the info when I get back