86' 420 High Idle Problem
 

Q. I just replaced the Idle slide valve on my 86' 420SEL. However, it idles a little high now.(1400rpm in park; 950rpms in drive) Hence, what adjustment should I make in order to bring the idle down to normal range.(750-900rpms in drive/park) Otherwise, the car drives fine.

Note: Interestingly, before purchasing a 380SE sometime ago, it had a high idle problem and my mechanic replaced a blown fuse that controls the idle in the main fuse box. And the idle returned to normal. Could this be the solution? Also, he checked the idle by using a special tool that looked like a long flat-head screwdriver to check the idle adjustment in the top of the air box. Thus, could this also be the solution? I appreciate feedback on this issue. Thanks!

Yes. It called the OVP relay. Check the fuses inside it or replace with a good one. It's a common problem.

the idle on an 86 420sel is controlled by a module behind an angled panel in front of pass.under glovebox.it maybe original and may need replacing.check if it's getting power.

You're right!
 

I stopped pass my mechanic's shop today and he showed that this was the problem. Hence, I ordered a new one to arrive on Thursday. Next week, this one goes in to be repainted. Thus, can't wait to see the results. Thank all for your feedback!