86 420SEL missing at idle, idle speed changes

[damon1172]

I have an 86 420SEL with almost 300k on the clock. For the last couple of years it has been misfiring a little, worse when warm I think. Last week it got much worse between start ups. Now it feels like it is missing on 3 or 4 cylinders and will barely idle. It also seems like if you step on the peddle a little bit it doesn't make any difference, step a little more and it runs worse, step even more and then it revs up to about 2k rpm. When it started missing a couple years ago I changed plugs, wires, cap and rotor but I don't recall it making a difference. I also ran a couple bottles of Seafoam through it to clean up the insides. Looking at other posts I see OVP, ICV and other acronyms I don't fully understand. I suspect these two are the overvolt relay and Idle Control Valve. Is that where I should start looking? Where are these devices? I have the manuals on CD and they stink. If I can find a section that talks about these devices it won't tell me where to find them. Also read something about injectors. Is that it a do it yourself job? Thanks in advance for your help

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[CLOCK123]

GET SOME INJECTOR CLEAN POUR IN GAS TANK DRIVE THE CAR THIS MAY HELP IF NOT REPLACE FULL FILTER ON THE RIGHT REAR SIDE OF CAR CLOSE TO FUEL PUMP MAY BE CLOGED UP TO CHEAP FIXES THAT MAY HELP

[damon1172]

Originally Posted by CLOCK123

GET SOME INJECTOR CLEAN POUR IN GAS TANK DRIVE THE CAR THIS MAY HELP IF NOT REPLACE FULL FILTER ON THE RIGHT REAR SIDE OF CAR CLOSE TO FUEL PUMP MAY BE CLOGED UP TO CHEAP FIXES THAT MAY HELP

I have run many cans of various cleaners through the car. Fuel filter was replaced less than 2000 miles ago. However I think I may have found the answer. When it started running extremely bad I took it to the shop. They ran smoke through the car and found a vacuum leak at one of the hoses. That made it run much, much better. It still idles a bit fast and changes idle speed but they also said there was a small intake manifold leak. Some day I will pull it apart and fix that leak but oh boy what a job!

Thank you for the good suggestions.