Irregular idle
 

Hi all.

Trying to help out a friend with his 01 F4i(13K miles). It had been put away a few years ago without any problems. We are trying to get her up and running again. What did we do?

drained the tank. No rust. Put in new fuel with injector cleaner.
flushed the fuel lines
removed the injectors and checked for visible dirt
removed the spark plugs, checked, didn’t replace
checked and cleaned the coils
checked FPR for leaks when removing the vacuum line, no leaks.
cleaned K&N air filter

the problem:

starting goes just fine. But it bogs and has an irregular idle. But when revvimg and back to idle, it runs fine a few moments and then it goes bogging again.

What order would you check the bike now? The parts are not cheap so i want to check in a logical order.

BTW: After first clean it ran fine. We rode it and no bogging at all, but the following day the problem occured again.

no fault light coming in btw

I would check if all 4 downpipes get hot after a cold start. See if it's running on less than 4 cylinders.

I did. All hot.

I would say buy yourself a cheap head gasket test that you stick on the radiator it sounds a lot like my bike did when it had a blown head gasket.