560sel duty clcle at 97.2%
 

i measured my duty cycle at 97% and turned the air mix screw and no change what do i check or do now? at idle i am very rough. new plug and wires and when you undo the icv the rpms go up. so where do i go from here?

Can't believe nobody responded to this...I am having a similar problem.

I had an '87 560 SEL with the same problem, my was started as an intermediate rough idle and changed to continuos rough idle. Recommndations that people gave me were as follows:
Check for vacuum leaks
Techron fuel injector cleaner
Change plugs, caps and rotors
Change ignition wires
Replace fuel injectors (irritating job, rubber parts, crack like thin walled glass)
Then when all these failed, and they did all fail, I took it to the dealer and they told me the fuel distributor was defective and needed to be replaced
$1,800 plus labor plus tax. I sold the car, not because it was a bad car, I just couldn't handle the bad idle, and was not going to put over $2,000 in a car that i paid $2,000 for in the first place.
I replaced it with another 560SEL, this time an '88. This one as well once it hit 127,000, same bad idle, replaced the same parts as before no change again, sold it againbecause the rough idle was driving me nuts, and replace it with a 300SDL.

So I can suggest you start with the vacuum leaks, then move on to , the fuel injector cleaner, you've already done the caps and rotors, well there's the ignition wires, then the fuel injectors. Then theres the possible diagnosis of the fuel distributor. My advice, don't fall in love with the car, and don't let it bankrupt you, there's alot of these out there at reasonable prices. If the idle bugs you and you can't fix it, sell it!

Had the same symptoms with 86 560 sel. Then one day it just quit no spark
replaced crankshaft position sensor.Idles great now.Who knew.

Your readings are useless so you need to find out why. In all instances of useless tool information one needs a standard. The standard here is the key on engine off duty cycle. On a federal car it is 70% on a California car it is 85%. Verify that condition and we can go from there.

Also the instance of a fixed duty cycle is often a code. The codes can vary but are usually not for 100% duty cycle (figuring 97% rounded off) as a pegged mixture is also fixed at the end points. This is why one needs to calibrate ones test and why more info is needed such as the year model.

ok here is what i have done.new injectors and seals and holders and hoses. turn on the key reads 97.6 crank it up will flucutate at 120 to 97,also it idles still no fluctuations. the one thing that gets me is when driving when slowing down the economy gauge goes into the red and sometimes just kills, why does this happen?

Your readings are still useless. There is no such thing as 120 % duty cycle. As in life 100% is all you get.

Your vacuum gauge readings are just a reflection of the way the engine performs. Engine dies vacuum dies. Lots of possible reasons, but if you wish to use electronic testing for monitoring and calibration you need to get you tool calibrated. There are a couple known quantities to line your tool with. The best is key on engine off. You should read 70%. If you don't chances are your tool set-up is the likely reason, especially if you ever read over 100%, which is impossible. You have to understand what you are measuring. You are measuring duty cycle otherwise know as on-off ratio. On all the time is 100% on duty cycle. You can't be on more than all the time.

560sel duty cycle
 

Th action of your "economy" gauge indicates a massive vacuum leak. Find and fix that first. It may solve all your problems. If not, you will at least be starting from a better condition.

My grandpas 560sel did that, I though the idle was cool :D. Its a vacuum leak also based on your gauges as stated above. For us it the filter housing in which itself and nearly all the vacuum tubes around it were knocked off. the car rocked left and right in idle it was awesome