If the tachometer doesn't start increasing, then the problem must be in the engines' fuel system.
Possibly a problem with air flow position(sensor) as it doesn't happen every time.
MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)