Rubber boot connecting throttle body to intake manifolds may crack on Mercedes-Benz 420SEL

The rubber boot connecting the throttle body to the intake manifold tends to crack. This can cause hard starting, rough or erratic idle, and engine performance problems.
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Average mileage: 225,200 (200,400–250,000)
2 model years affected: 1990, 1991
4 people reported this problem
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problem details
Came on slowly, until could not hold an idle at stop lights. Sound from under air cleaner is a loud whooshing sound like a vacuum cleaner. Also, I sprayed carb cleaner at the boot and the vehicle accelerated.