I have a 1998 190e that shifts hard when the outside temp gets over 75 degrees, I'm assuming that at that temp the transmission temp gets high(?). I did have the tranny serviced but the problem still exisits. At temps below 70-75 the transmission shifts smooth. The Vac. modulator was checked and seems to work fine. The motor is a 2.6L and the hard shifting is between 2 and 3rd. Any ideas ?

Vacuum issue, maybe? You could start by checking the line from intake manifold to the vacuum modulator. Maybe you have a crack in the boot at the intake manifold.

__________________
1990 190e 2.6 - The only one I can really call "My Car".

1987 190e 2.3 - The donor car's up and running, only mods are Euros and a Sony headunit. My Dad's runabout now.

1990 300e 2.6 - The parents' ride.

You mean 1988?

__________________
1992 190E 2.3
150,000 Miles

My typo......I have a 1989 190e. I will check the vacuum boot. Thanks for replying.

It does sounds like a vacuum problem. The first design modulators have a black rubber cover which is part of the cars vacuum system. Remove it and check it for a crack or loose fitting. They do crack. You can buy a new #126 277 00 81