Cold Up**** Delay Switch.
I believe that replacing it requires removal of the transmission but someone with experience might be able to do it by dropping the back of the transmission but it sure would be tight.
It is located behind the break booster cylinder in 104 engines.
The odd part, however, is that the switch itself does not go bad very often. Probably the problem is in leaking vacuum tubes either one that come in, or the one that leaves out. They need to be tested first using hand vacuum pump. They should keep pressure of 15 bars for 30 minutes.
If there is a leak, replace tubes first. Only as a last resort, replace the valve itself.
They quoted $250 to fix it all at the dealer.
The function of this valve is to delay upshift of the transmission when the engine is cold. This is done purely for emission control purposes. It cannot hurt engine.
Again, the only annoying thing about it is the "check engine" light.
Speaking of which, do not disconnect battery to reset codes. Here is the procedure to reset them:
Read all codes first.
After the first code is read again during the second go around, wait for 3 seconds and press the button for 10 seconds.
Repeat the last step for each code.
Turn-off and turn-on ignition.
Hope this helps.



