gunked up idle control valve
 

can you disconnect the idle control valve (1987 420sel) and clean it with carburetor cleaner?

how do you know if it is gunked up/or if the valve is not working?

lyle

I'd use electrical contact cleaner.easy on plastics

Yes you can. It has a flap inside.

you can but it not usually going to fix it. Where does your idle sit?

I tried cleaning mine on the 420SEL. It didnt really help all that much. My idle is just a few ticks underneath 1000. Sometimes It'll sit the normal 550 or so sometimes not.

A replacement unit is $185 or so.

Dang those things have gone up!!! Mine would sit about 1100 and cleaning would not improve the condition so I replaced it. I think I paid like $90 or so a few years back. It worth it. Saves your drive train from flying apart when shifting into reverse.