Need help on annoying problem & intakecleaning

[Paraklas]

My current car has an M40 4cyl 8valve 1798cc engine with a manual gearbox. Now it has 200000km on it but It has developed this problem for a year and so:

With no gear engaged, when I press the gas pedal up to the middle for example, the car seems a bit hesitant to go from idle to more revs. That is, hesitant just to get out from idle revs. Once it's even 100rpm more than idle, the revs increase normally. To explain it better, It needs 0.5 seconds to go away from idle and during that time, engine shakes a bit.

Also, when I press the pedal up to a point and then just leave the engine to come to idle by itself, when it reaches idle it goes down just a bit below normal idle and then comes back to normal idle.

I have:
Replaced oil/fuel filter
New engine oil
Fuel used: Unleaded 98 or 100 octane but no change in problem above
Installed K&N performance filter in stock airbox
Replaced Fuel Pump (broke down in the middle of highway grrr)
Replaced Spark Plugs (Bosch)
Replaced Idle control valve
Checked for vaccuum leaks and changed all those thin sealants (don't know how you call them in English) that seal the metal connected metal parts of the engine.
Changed all the rubber hoses of the fuel.

I really have no clue what can be causing that problem!


2nd, what's a good air intake/fuel line/injector/valve cleaner(s)?

Thanks for the help.
Paris