HELLO TO ALL
I have just purchased my first MB a 87 560sel with 150k miles and a idle problem. I am a auto tech by trade but have never worked on BOSCH CIS systems before so I figured WHAT A WAY TO LEARN! This car has been very well cared for and looks new and has thousands of dollars of receipts for service,most I suspect are from this on going idle issue.
Problem is the car has a very rough idle and will eventualy die.It runs fine over about 1000 rpm. I have checked fuel pressure upper 6.2bar and lower 5.8 bar. idle switch is working,Idle air control working ,air flow pot.working,new plugs, wires, cap, rotor, O2 sensor,crank sensor,fuel accum.
The only way I can get the car to Idle smooth is to adjust the on off ratio to 0% rich,O2 flat 1v. If I lean it up to any % duty cycle and O2 osillating the idle will get so rough it will die.It seems to be over correcting and staying lean too long. Also the car will run fine when cold in open loop.

Possibly you have a bad injector or un-equal delivery from fuel distributor.

Try finding the problem cylinder(s) with either an infra-red heat gun on the exhaust...OR by cylinder balance..

To check cylinder balance you will have to disconnect the idle valve & then squeeze (needle nose vise grips) the idle balance tube (hose) until the RPM is at 600. then see which cylinder is the weakest.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Friend,
Sounds like a massive intake leak. These engines were notorious for idle air distribution leaks esp. at the nozzle holders.
G'luck
dpk

Or a vacuum leak - have you checked all the rubber connectors for the plastic lines? Where is the "Economy" gauge sitting at idle?

Is the EGR valve working correctly? Try disconnecting and plugging the vacuum line.

Maybe an injector seal causing a lean idle misfire?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Hello all !
Thanks for the input. I will do more checking and get back with results.

CHEERS
JEFF