I Have a volvo 240gl 1989 model (fuel injected).
It has been running fine and i have just added in one of the full fuel system cleaners to my petrol tank. Now that i am about halfway through the tank i am getting some TERRIBLE problems. THe engine is drastically underpowered than normal (not that it is a gutsy car in the first place) and is sputtering. It seems that it is getting inconsistent power as it moves in "jumps". This is hard to describe but ill do my best. For keeping the throttle in the same position, over the period of say one second or 2, the power is alot higher for say half that second than for the other half. After afew seconds of keeping the throttle in the same position though it is not really noticeable. It is however noticeable when i try to accelerate.
Does this sound like a misfire?
I have just had the spark plugs, leads and fuel filter replaced recently (about 2 months ago) as well as the distributor cap. The mechanic said the injectors did not need cleaning as the fuel filter was filthy and caught everything?
could it be that the new filter is already clogged or that my injectors need cleaning?

Any advice or help in diagnosis would be great.
Also is there any simple method or tool to detect a misfire?

Best Regards,
gonzad