On my D15B2 engine, when I try to rotate the throttle valve when the engine is running, it runs not smoothly, but it jumps a bit near the idle position. When I turn the throttle while the engine is not running, the throttle runs nice smoothly! What the hell can be this, when the smoothiness is different when the engine is running and when it isn't? Also, there is a little play in the throttle axis when the engine is stopped, but it gets away after I start the engine.

Any thoughts what can it be? It's not in the accelerator cable, since I am rotating the throttle directly in the engine compartment.

Thank you,
Petr

 

are the bolts snug?

butterfly may need to be aligned.