I put the chart on how to check the Engine Temp Sensor in the EHA thread below, it is for an M102 and M103 engine, which I would think you have the M102 engine on yours.

As for the vacuum modulator it is on the left hand side of the transmission. Mine jerks as well when floored and Kickdown is engaged from 1st to 2nd. Not during a normal shift which occurs at 4000 RPM on my 190E. I always attributed it to an issue with the low gearing for 1st gear shifting at high RPM to the next gear. I get a tire chirp on mine and spinning in adverse weather conditions.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....