I noticed today after starting my car that one of the accessory belts squealed horribly when I revved the engine slightly after starting the car. I thought that was a bit strange as I had just replaced all of the belts. So, I started thinking that perhaps the air pump was locking up. So, I unplugged the clutch for it, so it could no longer engage. It fixed the start up squeal and the start up roughness. Or at least it would seem that way right now. I have only started the car a couple of times since doing this today, but it does seemed to have fixed it. The air pump must be seizing up and just lugging down the engine on start up.

I'll let you know if this has actually resolved my issue in the coming days. Thank you everyone for the quick replies.

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1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car