I bought a 1997 E320 that had overheated before.I got the car checked out, replaced the head gasket and water pump due to damage from the overheating.Now,when I start the car,it knocks loudly and I have to pump the gas pedal to help it start.It does start all the time when cold with the knocking still there,then when the engine is warmed up the car does not turn on all the time when hot,it will only turn on sometimes.The RPMs bounce up and down and sometimes drop to 500 to 1000,but the car never shuts off by itself it will always stay running,however the knocking sound is still there.The engine temperature stays perfect the entire time.Any ideas on what this could be.

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1998 S500
2006 E320 CDI
1963 220S
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1995 S500
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2007 GL320 CDI
2007 ML320 CDI
1991 Toyota Previa White over Blue
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