GT40 engine loping

On the cleaning with a cotton swab, how can you clean around the valve seat since the valve is closed? Is it possible to carefully open it manually to clean the seat?

It also comes up with these motors that the fuel control relays can be troublesome.

I've also read that there is some kind of a clear tube within the Fuel Control Cell (if your boat has one) that can develop a crack and cause fuel pressure problems.

Also, fuel pressure regulator has come up as something to check.

But, usually problems that are related to temperature are often electrical in nature.

Okay, so I pulled the IAC (ISCV) and cleaned the orifices in the throttle body, including the screen. The ISCV I pulled out of my car actually seats in the throttle body, so it is easy to clean where it seats after you've pulled it out. However, since the valve seat is part of the IAC, I can't clean that part.

My question before I start spaying the inside of the IAC on either side of the closed valve seat, I wanted to make sure it is fine to spray throttle body cleaner in there. I don't want to short it out, so would appreciate advising the best way to clean the valve (and seat).

Thanks,

Gordon

Idle air control, as Luch suggests

I have always had a bit of a problem with engine loping. It will do it when very cold (winter) when launching, and also do it when the engine is hot and it has sat for a while (30 minutes or so with the engine compartment closed). The warmer it is, the worse it is (really bad in the summer).

When it is cold, it can last for 30 seconds or so but then smoothes out without doing much of anything. When it is hot, it can last that long or up to a minute and be bad enough that it stalls. Giving it throttle helps and speeds up it getting back to normal. I have no idean on the problem when it is cold, but I would suspect vapor lock when it is hot. But with MPFI and high pressure pump, I don't know how that would happen.

I have not put a pressure gauge on it to see if the pressure is going up and down when it is loping (I am in the process of replacing my original GT40 heads with new ones, so it will be a week or two before I can put it back in the water and test). I did have my low pressure pump fail last year and I replaced it (made no difference for this problem), and have not seen any problem with the high pressure pump in the fuel canister.

But since it is a continual and ongoing problem, I'm hoping someone has a suggestion.

Thanks,