to check the turbo, make sure the engine is off, then remove the tube going from the air cleaner to the turbo inlet. then wiggle the turbo prop. there will be a lot of wiggle, about 1/4 inch from top to bottom, if the turbo is worn badly.

also, typically when the turbo is failing, you will get smoke in heavy acceleration, and another puff when you let off the pedal from hard acceleration.

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1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped