Hard start, bouncing idle, and no power all solved! - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 06-12-2012, 07:09 AM Thread Starter
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Hard start, bouncing idle, and no power all solved!

Hi, I'm new here, but I want to share some solutions I found for my 1986 420SEL.

Car had trouble starting, especially when warm. I removed the fuel filter and discovered it was hard to blow through. I replaced the fuel filter. Now it starts quickly. (Note: I had trouble with the cheap WIX filter, it was too small to fit the bracket, the connection leaked. I returned it and got a Fram which fits well. In retrospect I would have gone with a dealer filter, since it was about the same price as Fram.)

Bouncing idle. When cold it would idle at 550 rpm, then rev to about 800 or 1000. I adjusted the lambda screw. I had a bit of trouble finding the right setting - but it made the car run much better. The revving idle indicated it was running lean, so I tightened the screw a few degrees at a time. When I went too far it started hard, so I backed off a bit, and now it runs very well.

Poor power. Would not rev past 1800 rpm when driving, could barely climb hills, it reminded me of a newer car being in limp mode. A friend discovered the mechanical throttle linkages were gummed up. We lubricated all linkages (especially the ones on top of the block under the air filter box), now I've got normal power again!

Good luck!
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post #2 of 2 (permalink) Old 06-12-2012, 11:53 PM
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