My boat went basically unused for almost 2-1/2years. I have twin built 502EFI's that have been great for a long time. I put additives in to help store the fuel. I had a marine tech replace the IAC because it wasn't functioning when main butterfly was closed. The motors seemed to idle pretty good at that time but I didn't take it out of the slip. Marine tech said the fuel smelled bad. The boat sat for a while longer.. This June I sold my lift and put the boat on trailer. It was almost impossible to park.When I started the engines again they ran like 3 plug wires were missing. Motors really unresponsive, wouldn't idle in gear. When I did get the boat on trailer I pumped about 60 gallons of old gas out of each tank. I emptied them. I replaced all 4 fuel filters at that time and also changed plugs.Filters had water and debris. I put 25 gallons of 91 no alcohol gas in each side and took it to the water. It did run a little better but not great. It was suggested that I put some injector cleaner in the gas. I did. Engines started fine. Still poor idle in gear. We did about a 10 mile run at about 3200 RPM. Throttles not even with each other but running kind of OK. I did a pretty sharp sweeping left turn and the starboard engine kind of stuttered real bad, Tach dropped momentarily but the motor caught up again. I went another mile and did same sharp left turn and starboard motor did the same stutter again. I headed back to broker marina I was parking boat at. When I got to idle speed headed toward dock I was able to steer and dock the boat with the drives with engines at idle. I considered that a good thing and maybe a small measure of improvement. Maybe the fuel injection cleaner additive had some positive effect.

Anyone have some advice on the engine cut out on turn ? I've already been advised to leave the drain plug out so no need to go there. Sorry so long but I'm hoping guys with knowledge might use all the info to give me some good advice.

Running injector cleaner helps, but I would pull the injectors and send them off for cleaning and flow testing.

Remove the rail and fuel lines between filter to rail and clean them

That old fuel sat in all those parts and just gummed everything up