Condition and verifiable mechanical condition are everything when it comes to these cars. No acceleration could be a number of things from very simple to very complex but tends to be simple.

Is the car on a used car lot? If it is don't believe anything they say. Have the car checked out by someone you trust. Have a compression and leak down test if possible. Have himn also give it a once over to look for anything that might need to be fixed. How much is the car going for? Can you post any photos?

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Doug

1987 300TD x 3
2005 E320CDI