spy1

Hey guys i've been having some rough idling issues with my 84, 190e lately.
this started just after i had the engine steam washed, though i took care to protect the electrical vitals e.g. coil, ignition distributor, alternator etc.

i have traced the rough idle to cyls. 3 & 4. they seem not to be supplying any power at idle (i.e. unplugging the spark plug leads at idle makes little difference to engine operation)
however this effect is reduced at higher rpm and runs better at higher engine speeds(3000 rpm)
cyls. 1 & 2 run just fine all the time.
i have checked the plugs, cleaned and rotated their positions (no results)
checked and interchanged the spark plug leads (no results)
checked and cleaned ignition distributor cap & rotor (no results)
checked the fuel delivery to the nozzles via the fuel distributor (uniform & normal)
cleaned the fuel nozzles (spraying fine)
the car drives well on the road at higher speeds 40 upwards
however at idle speeds cyls 3 & 4 seem not be supplying any power.
i need help guys!

vanir

Re, the engine steam wash, as far as damage goes the thing to avoid hitting with pressure wash is the ecl unit, which is up behind the firewall under the windscreen compartment anyway, next to the battery. The (spark) distributor is pretty well waterproofed complete with gasket and outer cover due to position, so unless you're pointing the water nozzle directly at it actually trying to get condensation in there you'll be safe. The only drama prone area is the plug wells hold some water particularly towards the rear, warm engine, sends some steam and condensation up the lead.
But this is an easy fix, pull off the leads and blow out or let dry the water out of the plug wells (with a warm engine, maybe 5 mins), then liberal spray of non-conductive water-repellant like WD40 inside the lead and around the plug and off you go.

It seems a bit strange that the problem would start right after the engine was steam washed and could be anything other than water in the leads. I really don't think your injectors suddenly picked that moment to clog up, or individual plugs suddenly decided to corrode beyond use, the ecl, dizzy and coil needs to be sprayed directly with a concerted effort to water log them. It's got to be the leads.
Spray some WD40 up those bad boys and try that.

spy1

vanir, thanks for the response.
i tried WD40 on the plug leads after drying them out, when that gave no results i replaced all 4 leads.
You mentioned the ecl near the battery, i take that to mean the jetronic control unit.
i'll try a replacement unit as soon as i get my hands on one.
thanks again for responding, i'll update as soon as i get done.

vanir

If you can do so inexpensively that's all good, but before I went spending a lot of money replacing things I'd want to make sure it wasn't the simplest possible cause, again referencing the fact the trouble started right after an engine wash.

You'd only have to spend labour cost for example for a qualified Mercedes workshop to have a look over all the electrical/injection/spark system connections around the engine to make sure something wasn't dislodged or waterlogged by the pressure wash.
It could be as simple as the temperature sender to the control unit (which retards spark at high temperatures, couldn't help idling at normal temperatures...).

I mean unless you put the nozzle right into the battery compartment and sprayed the control unit itself should be okay.
Only after experts checking it's not just some loose connection (a Merc workshop has things like diagnostics instruments and plenty of experience), which shouldn't really cost you an arm and a leg, then I'd look at coincidental failures...but again only moving from simplest/cheapest first.

What I do with mine, like any 20yr old car that's been passed around a few times it has occasional odd little quirks, is start with the cheapest/simplest generally related items that are old/worn and could use replacing anyway, eg. I was having a rough idle when I first bought it for a few minutes after startup but it hadn't exactly been getting regular services from the last owner (his wife's sunday driver, at least it had low kms), so hell pretty much all the electricals and general service/maintenance items need replacing anyway. So I just went through them with new items until I hit the one causing the problem by chance (it was elec.dist., rotor corrosion, bad plugs and a coil lead; but also a fuel leak in the fuel dist. wasn't helping so replaced that and all the seals too, and a fuel pump).
Point being I still got value for money on what I was replacing because even if that item wasn't causing the specific problem, it needed replacing anyway.

Try to use that philosophy I reckon, before spending money replacing more expensive items that might be working just fine...unless you know it isn't. That way every dollar you spend is worth it either way.

DRACO

You probably have a vacuum leak, check all vacuum lines are secure, the power washer may have dislodged a hose or worse broke it.

Turn the car on, remove air filter box, if electrical is connected to it like my 8v then just move it our of the way and spray some electric parts cleaner or carb cleaner and spray around the hoses and injectors. Do a little at a time so you won't get a false positive.

This is how I found my leaks at the breather hoses and injector 4 seal.

Jim

spy1

Thanks Draco,
i already checked all the visible vacuum lines for possible leakage, i haven't found any.

spy1

I finally discovered the cause of my rough idle problem.
It appears poor combustion due to restricted airflow to these cylinders was the cause of my problem.
Tweaking with the mixture control screw finally evened out the combustion inbalance in cyls.3 & 4.
Still beats me why this effect is more pronounced in cyls.3 & 4, moreso why this should come up after an engine wash.
Anyway my 190 is back to normal and purring smoothly like a well fed cat.
Many thanks to all for your concern and contributions.

vanir

I'm very glad it's sorted for you but the solution has me totally stumped.

The only abstraction I can come up with is gunk buildup around the valve seats. Did you richen or lean the mixture?
Either leaning might have burned off the residue or richening might've compensated for leakage.

I'd seriously consider a compression test and head/chamber cleaning. They do build up a lot of residue, when I had my cam installed the mechanic said whilst existing parts (valves etc.) were all in excellent condition, he spent most of the labour time cleaning gunk and residue.

It's fairly typical for inline engines to run richer at the rearmost cylinders and leaner at the frontmost, acceleration likes to move everything towards the back. Should be less of a problem with injection than multiple carb setups but then the CIS-E is part mechanical in operation. Richer running builds up more residue.

But you should've noticed this when you pulled the plugs. Rear ones should've looked different to front ones.