There was a recall involving something to do with the throttle on these cars that Benz may still be honoring. It's been only a few years since they "fixed" mine on my 89 300E even though it wasn't exhibiting any symptoms. They actually notified me by mail! I had them check my 88 300E too but they said that that one had already received the "fix". You should look into that recall.
Regards, Eric

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89 300E "Benzer1" 15.924 Uncorrected
93 400E "Benzer3" 14.200 U.C.
95 E420 "Benzer4"
92 300E "Benzer5" 16.299 U.C. Future turbo CNG
87 300D "Benzer7"
87 300D "Benzer8"
87 300D "Benzer9"
87 300D/70 AMC Javelin "Sidewinder-Benzer"
87 300TD "Benzer11"
06 E320 CDI "Benzer12"
05 E320 CDI "Benzer12A"
71 AMC Javelin AMX 401 "Sidewinder"
74 AMC Hornet 401 "C.K.10" 13.63 U.C.
74 Bricklin SV1 "Presto" AMC 360 pwrd.