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1967 Unimog 404
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Discussion Starter #1
Hope somebody can help with this...1986 560sl with 118,000mi, bought it on eBay, and am doing lots of work to it. Idle is really rough at about 500rpm, tries to increase, bumping up to 700, then dies back to 500. It used to do this only after being in traffic for while, now all the time. I thought it was the injectors as it was a bit hard to start, and burned rich upon start up. Replaced injectors, seals, sleeve o rings... no change. Then thought maybe it was the air hoses to the injectors, so just replaced those. Thought maybe the idle control unit, so swapped it with a spare, no change. Car runs fine once off the idle and through the gears. No evidence of any other running issues, only at idle. Once I started it after a few days, and instead of idling at 500rpm, was at 1300rpm....Hmmm
Any ideas, anybody?
 

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BenzWorld W126 & W201 Host
1988 420SE, 2002 C180 Kompressor, 200 ML320
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1,159 Posts
Bad idle

lawrence

Your initial description of the engine running at 500rpm, trying to increase and then dropping back down strongly suggests you have a vacuum leak causing the engine to hunt. As you have tried injectors and seals, my next guess would be the inlet manifold gaskets.

To check for this, leave the engine idling whilst pouring water over the the joints where the manifold meets the head. If there is a leak, the water will get sucked in, the rpm will increase briefly and you should be able to pin point it.

Not sure about the fact that you say it's now idling at 1300rpm.
 

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1967 Unimog 404
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19 Posts
Discussion Starter #3
Thanks, looks like you are on the money. The tech at the dealer diagnosed the fault as ...

Thanks, looks like you are on the money. The tech at the dealer diagnosed the fault as a major vacume leak from the throttle body assy area. Reccomends replacing throttle body and rechecking. That souds like the expensive way, so what I'll to is take the fuel distributor off, the throttle body off, and replace the o ring and gasket. If i find nothing I'll pull the intake manifold out and but everything back together with new rubber and gaskets and see what happens. I hope it works this time.... Any advise? Is it worth doing the throttle position switch at the same time, does it wear?
Cheers, Lawrence.
 

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i had the exact same problem with my 86 560sl, idling a bit for a week or so then starte...

i had the exact same problem with my 86 560sl, idling a bit for a week or so then started getting worse ... they changed engine cabling, spark plugs ... 300 canadian each, 600 total plus labour ... expensive but fixed it right away.
 

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1967 Unimog 404
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19 Posts
Discussion Starter #5
more shitty idle/over voltage relay?

Shitty idle...

Well, going on the premise of a vacuum leak, I decided to basically rebuild the injection/intake system in the car. So new injectors, sleeves, o rings, air supply hoses, air duct housing, throttle position switch, gasket, the 8 rings between the airbox and intake manifold, the intake manifold gaskets, fuel distributor o ring. Also checked all the vacuum lines and replaced all the worn hoses and connectors. New plugs and wires. Essentially every rubber hose, gasket etc. plus the new injector assy's and new throttle pos switch.

A slight improvement, but still idles at 500rpm, with really jerky transmission engagement. Tach sometimes craps out but only when engine idles-running through gears it's fine. Sometimes I hear an audible click and the idle changes 200rpm.... So, I guess now we look for and elecrical problem. I swapped the idle contol unit with a spare and no change.

I figure the next part to throw at it is an over voltage protection relay, so bought that and will give it a shot. Anybody know where it is on a 86 560sl?

Any comments, advise?

Cheers, Lawrence.
 
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