Newest Mercedes in my bunch, 420SEL
 

I just bought a minty 89 420SEL and the only things I can find to look at are as follows:

1. A/C is a little slow to come on after the switch is pushed; works fine after that .... has been converted to 134A

2. Security alarm is very sensitive; seems to be affected by heavy wind, etc. etc. occasionally. Can this system be adjusted to be less sensitive?

3. A slightly rough idle; higher speed performance and starting are fine? I will look at the obvious -- such as vac hoses and plug connections, but what else might cause this?

Would appreciate any thoughts on these items .... thanks, Ben Carter

Number 1 - if it is on auto. it will take a second or two to come on. If not - mine does the same thing. I am not sure why. Several other friends that have the 126 chassis cars do the same thing.

Number 2 - my parent's '88 300SE has the same problem. It is in the switch in one of the doors - it is connected to the door handles. They elected to just disconnect the alarm - under passenger side floor mat.

Number 3 - could be several things. Have you checked previous maintenance records to see if the plugs, wires, rotor button, etc. have been changed? It could be the OVP (as mentioned in several other posts). It could be a vacuum leak. It might be worth taking it to a reputable independent to see what he can find for you.