slk230 throttle problem
 

My 2000 SLK230 runs smoothly up to about 4000 rpm and then stops accelerating. I repeated this in Park and the engine revs up to about 4000 again and won't go any higher. I changed the fuel filter earlier so I can rule out that. Does anyone have an idea if this could be related to something in the throttle position sensor?

Any codes..check engine lamp?

Don't have anyway to check the codes and no check engine lamps on.

Thx