Rough idle on 560 has been a problem ever since I purchased the car last August. I have been in the trouble shooting mode reading the engine manual several times..I had found a bad throttle switch and leaking EHA. Replaced them, but the idle was still rough. This last week I pulled out the injectors and in looking down the holes I saw broken tips on the nozzle holders. I replaced all eight nozzles holders, guides and vacuum hoses on top of the injectors. That fixed it !! The engine has a smooth idle and the acceleration improved considerable. All this for a little over $50.00. The car is 10 years old with 130K miles. All the engine rubber is quite brittle. I think this could be a source of problems for all the old CIS V-8's. Thought I would share this with everyone.

H. O. Tyler
90 560 SEL 130K
85 300 SD 62K
83 240 D 260K

thanks for the information. might need it someday....

emmy
1991 560SEL 125K

I HAVE A 300SEL 89 AND HAVE A ROUGH IDLE FOR A LONG TIME. THE TECH TOLD ME IT COULD BE THE MIXTURE CONTROL UNIT BUT DUE TO THE COST I DID NOT FIX IT. I DID HAVE MY INJECTORS CHANGED A FEW YEARS BACK. WHAT EXACTLY DID YOU CHANGE THAT CURED THE PROBLEM. APPRECIATE A RESPONSE FROM YOU.

I changed out the fuel injector nozzle holders and rubber vacuum hoses. This is a 560 V-8 gas engine with the CIS fuel injection. The 420 is simular.

Can you please specify the symptoms of the rough idle because my 420 is having problems. It idles smoothe and like every five seconds it gives a jump shake like a piston just fired. Thank you.

Mike