1989 r107 300sl Starts but wont idle.

[Dontastic]

Hello Mercedes enthusiasts i hope this finds you well.

My 1989 300sl has developed a bewildering display of non/poor running symptoms and having spent the last few days learning/studying all about the ke jetronic system im well informed but still slightly confused as to the exact fault so here goes: Now i may not of gone about this in the correct order but went about it nevertheless.Lol.

She(or He@the risk of sexism!

) was running great,then started idling a tiny bit rough and became difficult to start when warm so i changed the plugs,air filter,distributor cap,rotor arm and fuel filter all of correct specification and that didn't make the difference i was hoping for.

Then the economy gauge ceased working,stuck to the right(Red)but still ran ok ,if but a bit rough.

Later when attempting to start warm a LOUD! backfire occurred and NO Starty:fail.Towed home and set to work on diagnosing problems.
Started with a check of all vacuum pipes and Bingo!(No thxs! lol) found the inlet manifold grey vacuum pipe off so plugged back in and...nothing

.Further up the pipe found where splits into 3 check valves one of which had almost disintegrated but was able to tape up temporarily so as to eliminate and she now starts(And economy gauge works too!) but will not idle without manual use of accelerator and really rough even when kept running until up to engine temp,still just stalls.

I find that if i disconnect the idle control valve(been removed and cleaned and shown to close when voltage applied) when warm she will idle on her own but a little high 1000-1200rpm and as soon as i re connect it cuts out.

Poss engine temp sender?
Poss cold start valve?
How can i check idle valve.cold start,engine temp sender correctly?
Is it lamba sensor,how to check?
I also have a new ovp relay fitted.


I think i will stop there,have some lunch and rest my head while eagerly awaiting some replies from you amazing r107 specialists!!

 

[Dontastic]

Any thoughts guys? Plz!

 

[Druk]

Have you checked all the pipes from the ICV to the K-Jet unit. If you get a manifold backfire (and that's what it sounds like you've had) it can blow the pipes off their connections right the way back. Also check them for splits by squeezing them oval. I suspect a manifold leak.

 

[219]

I had the exact same thing years ago with my 300TE - same engine .

Started , got a loud 'pop' and could not fathom out what was wrong . AA man was baffled too - he used the 'phone a friend' option , who told him to check the breather pipe on the underside of the inlet manifold . It was very hard to see , never mind reach , but it had blown off and , once put back , the car ran fine again .

 

[Dontastic]

Great advice guys thanks,and along the lines i was thinking,ive heard about this elusive breather pipe under the inlet manifold.Just a thought but it isnt the pipe that comes from the bottom of fuel distribution unit to the icv? but thats not under the manifold!

 

[Dontastic]

Hi guys an update;
I have been to a few garages in the hope of finding a good mechanic but not impressed by any of them ,with one quoting"i dont really want to get involved in that kind of stuff" lol What ur job u mean!.
Anyhow got back under the bonnet and after more intricate diagnosing came Back to the idle control valve again to find it stuck closed,so removed and cleaned thoroughly with wd 40 (bathed it in it!) which got it working again nice and smooth put it back on and Bingo straight to 1800rpm, then slowly came down to 600-700 then when warmed and left running went lower then shot up to 1800 then 800 then 1800 etc etc.Now i pulled the pin plug back just enough to get some probes on it and this is whats happening=

When cranked up theres 3.0V when @5-600rpm then voltage slowly goes up to around 7-8v before engine idle jumps to 1800 and will only come down with a big throttle blast or by gently tapping the ICV !!,and u can set ur own idle temorarily with the tap method! but go to low or after any throttle input she goes up 1800rpm and stays there till throttle input again then almost stalls @500rpm until 7-8v reached@icv then 1800 again.

Surely this is a tired ICV? But wanted to check with you guys.
Any Thoughts

 

[Dontastic]

Hi a new(used) icv turned up today and its totally solved the problem.

Better still i have become an expert on 300sl idle problems and in the process of eliminating this one all the parts involved were cleaned/serviced and it turns out even with slight vacuum leaks these rock solid engines still run sweet as a nut.

I hope the icv diagnoses can be of use to anynone else with idle/start problems.

 

[RiccardoG]

Hello Dontastic, slight thread resurrection here but my 1989 300SL also seems to be adverse to cold starts and I was hoping to use your experience (if you're still on here).

Basically it will turn and switch on when stone cold but then sputters and shakes a bit and dies. It will start ok second round but idles very low (~800rpm) before eventually settling down. Sometimes it takes three tries.

How can I locate the ICV you mention and also what vacuum pipes did you change, if any?

Do you have a part num (and cost) for the new ICV?

Thanks in advance!

 

[Dontastic]

If its not the icv it could be the ovp relay,cold start valve