mercedes clk 200 auto 1998 petrol&gas?

What kind of car are you talking about. What kind of engine does your CLK have? Four, six or eight cylinder? What kind of fuel are you putting into your CLK? I thought petroleum and gasoline come from the same place.

I am confused by your question. What is a gas conversion??? I get the feeling that you may be talking about the catalytic converter. Most problems like this, if I am understanding you right, are due to a dirty IDLE AIR CONTROL VALVE. Remove your air intake boot. There will be rubber hoses leading to a silvery cylinder, about an inch and a half in diameter with an electrical connection to it. This is the IAC valve. When it gets dirty, it alters fuel mixture and may eventually cause a clog in yout converter. Remove it, clean it with Gum-out. Clean ALL rubber hoses here, and the PCV hose and valve. Return the valve to service, and spray the rest of the Gum-out through your air intake. This will clean the O2 sensor, and the converter when you race the engine. If this is NOT the problem, E-mail me back, and I will try again! Don't even THINK about disconnecting your converter. You will have a smelly, gas-eating mess on your hands. If you were in the Detroit area, I would come out and service it for you!

Get the Gas conversion removed, nearly all Merc's have problems when they are run on gas after a long period of time. At least then you will be able to get the fault diagnosed properly if it's still there.