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  #1  
Old 11-11-2008, 08:54 AM
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Join Date: Nov 2008
Posts: 7
1990 300ce erratic warm idle

Hi all, I'm a newbie on here, and wow what an amazing mine of information.

I've been through many similar threads but none quite seem the same.

Basically the car starts fine and runs sweetly, slowly settling to around 6-700 rpm idle and stays this way for approximately ten mins and then begins to run rough, smells rich and idle will flutuate between normal and around 1500. If I blip the throttle sometimes it just returns to 1500 and sometimes it will go lower and surge, once or several times. I have stripped and lubed idle contol valve and checked ovp relay. Plugs are recent as is dissy cap, and all vac lines seem ok.

I don't know whether it's just not switching to the warm cycle (maybe temp sensor?) and that is causing the overfueling, or if it may be something else entirely.

Any comments or similar problems solved would be most appreciated.

By the way it's the M103 3 litre 12v SOHC engine.

Regards

Chris
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  #2  
Old 11-12-2008, 07:29 AM
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91 300CE M103: 80 450SEL
 
Join Date: Nov 2001
Location: Dublin, Ireland
Posts: 112
check sensor resistance

I had similar conditions to yours a few years ago. You can get the resistance values of the temp sensor by doing a search here. Its the 4 pin one at the rear of the head.
Are your plugs the correct non resistor type?
My rough running was a combination of wrong plugs, some vac leaks and distrubutor fuzzing up. all at various times making it hard to pin down. Ensuring I used non resistor plugs cured the dizzy cap fouling up. Dont accept the "thats what the books says" answer that the parts shop man/kid gives you. Get a bosch H8DCO or NGK BP6EFS.
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  #3  
Old 11-12-2008, 08:04 AM
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Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
If you have a DMM (digital volt meter) & can check the duty cycle WHEN the problem is occurring, most likely you will get a fixed reading.

That fixed reading should show what is causing your problem.

Is the secondary ignition system in good condition?
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  #4  
Old 11-12-2008, 08:40 AM
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Cheers guys

I was having a problem with starting generally as the car had been stood for quite sometime so I removed the dissy cap and cleaned all the contacts and the same with the plugs. Not sure what type the plugs are but will check, they are just the ones they sold me at Euro Car Parts.

In respect of checking the duty cycle, which terminals, sorry for appearing a little dumb but which terminals do I go across and should I check resistance or continuity during cold running and then once warm?

Many thanks again

Chris (Manchester U.K)
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  #5  
Old 11-12-2008, 08:42 AM
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Join Date: Mar 1999
Location: Tucker, Ga USA
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You check "duty-cycle" on pin #3 of the round connector & a good ground.
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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator
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  #6  
Old 11-14-2008, 06:36 PM
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91 300CE M103: 80 450SEL
 
Join Date: Nov 2001
Location: Dublin, Ireland
Posts: 112
Quote:
Originally Posted by pugboy View Post
Cheers guys

they sold me at Euro Car Parts.


Chris (Manchester U.K)
They sold me the wrong ones too, when I asked to verify, they told me it was what was in the book. I now get non resistor plugs from a better supplier.
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