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Old 06-20-2009, 11:57 PM
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Join Date: May 2008
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1987 W126 Cold Start / Idle Problem

I have a problem with my 1987 420SEL regarding a starting issue when the engine is slightly warm, taking two tries for the engine to catch. The problem has now progressed to a completely cold start too. The problem still exsists and now the engine idles a little rough until completely warmed up. I have replaced the Idle Air/Speed Control Valve and a Engine Temperature Sensor. Since that didn't solve the problem, I then replaced the Cold Start Valve, or Cold Start Fuel Injector and the gasket.
After replacing all three of those parts, it hasn't solved the problem; in fact, it's a little worse now, with the rough idle lasting a lot longer.

Some months back, I replaced my leaking EHA with a used one from ebay. After I replaced it, I don't remember having the cold start problem right away, though it could have and I just didn't realize it; in my mind, it's kind of progressed over a period of time. I looked at all the vacuum lines and such, and all appear to be okay, though I can't necessarily tell one isn't bad. I don't readily see anything that is amiss and don't see any fuel leaks. I also checked the 10 amp fuse for the Overload Protection Relay and my ABS light works, but is not 'on', indicating some kind of problem. Looking at the service records, it looks the O2 sensor was replaced about a year and a half ago.

Poking around the forums and auto parts sites, I came up wondering two things: is the Electronic Control Unit (ECU) the same thing as a MAS Control Unit, or are they one and the same and two, if my MAS was acting up, would that be a likely part that could cause the poor cold starts and rough idle?

Anyone have some additional thoughts on what to try next? Taking it to an indie mechanic certainly comes to mind but then that's admitting defeat...

Thank you-

Richard
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Richard / E320

2001 E320
1987 420SEL

Last edited by Richard / E320; 06-21-2009 at 12:15 AM.
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Old 06-23-2009, 09:36 PM
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Join Date: May 2008
Posts: 5
Took my 420SEL with a cold start and idle problem in to be checked out; came back running a lot smoother. Turned out that I had three vacuum leaks; one was at the idle speed control valve that I just replaced and there were two disconnected hoses, located behind the passenger headlight (switch-over valve for the air injection? Two light-blue, small diameter hoses, one with a red stripe and one with a blue stripe.)

Additionally, the tech reports that it had incorrect spark plugs (he replaced all eight) and the #3 spark plug connector was not on tight and had minor ‘corrosion’ from arcing. Definitely runs a lot smoother and started with the first key-turn running errands on the way home. I’ll find out tomorrow morning how she does on a cold start.

The tech also recommended that I replace the old style metal injectors and recommends replacing them with the newer copper style injectors, along with the seals and stands, whatever that might be. Is that a DIY project?
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Richard / E320

2001 E320
1987 420SEL
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Old 06-23-2009, 09:36 PM
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