so im yet to do an overall service on my 1month volvo 850 t5 MT , beside some things to look around last owner changed belts and service it 2 years ago
car runs ok. under some heavy deceleration, like in 2nd flooring it and letting off the throttle at high rpm range , the car have a misfire or what it feels as ignition with an open exhaust valve, also on iddle when the engine is hot and has been used a bit, it misfire as "burps" , always the same one not random ones.

hoses looks ok, ive changed some vacum dryed ones just in case, and patch a whole in the intake one
i could not manage to read codes , I'm gonna build a led reader


what should i try first before opening the head?
what about the camshaft position sensor?


thinking to test compresion on the cyl's as an easy way to see how are the gaskets