My 1995 E320 starts fine when the engine is cold, but when it is hot it fails to start. The engine turns over and I can hear the fuel pump working. If I depress the gas pedal about 2" and turn the engine over it starts ok, when I let off the gas it hesitates and run rough (low rpm) and then smoothes out.
I tested the built in led (OBD1) and got a fault code 25 "knock sensor" only. Could this cause the problem or should I look elsewhere?

 

your exhaust system is not blocked?

 

No, it's not blocked because once it's running it runs fine.
I checked the ovp, I replaced it a while back and it is the new style.
Where should I look next?

 

try cleaning the throttle valve first. i think the idle air is not enough.