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#1
02-01-2008, 11:51 PM
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1987 420sel high idle/cold start issues
Hi guys this is my first post so bare with me...I have an 87 420sel with 300,000kms. It is idling around 900-1000rpms in park and 700-800 in drive. I've replaced the idle control valve, idle relay, ovp and vaccum lines have been replaced, yet it still wants to idle a little high. Also in the last few weeks the car is hard to start when the engine is cold, it cranks 5-10 seconds before it starts, then takes a few seconds for the idle to smooth out. It only does this when cold, once the car is warmed up it runs fine, it doesn't stall or run rough and i don't see any smoke out of the tailpipe. I checked the cold start valve and there is fuel coming out of it when the engine is cranked. Any ideas/fixes would be much appreciated. thnx.
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#2
02-02-2008, 03:30 AM
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Mine runs at about 1000 rpms for a short while when its cold, then after 5 mins. or so it returns to 700. Does yours return to 'normal' after a while?
If you have a dud temperature sensor it might cause a high idle. When did you last change plugs/cap/rotor?
__________________
1991 300 SEL 218,000 Km "Xsbank's rules of mechanical intervention: Always go for the easiest solution first; 90% of what ails a gasoline engine is ignition; After that its all a WAG."
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#3
02-02-2008, 06:33 AM
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Sounds like vac leaks and throttle linkage is off. My 560 exhibits higher idle in P than necessary.
__________________
I'm not a doctor, but I'll have a look.  '85 300SD 245k '87 300SDL 251k '90 300SEL 326k Six others from BMW, GM, and Ford. Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]
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#4
02-02-2008, 01:12 PM
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Is the idle switch closed, is the airflow pot output below .7v? Do you have a vacuum leak.
__________________
Steve Brotherton Continental Imports Gainesville FL Bosch Master, ASE Master, L1 33 years MB technician
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#5
02-02-2008, 01:40 PM
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the idle drops down to "normal" range intermittently but for the most part its 900-1000 in P and 7-800 in D. There are no vaccum leaks to be found and the cap rotor and wires have around 10,000kms on them. Just as a side note when i bought the car the cruise control had been disconnected and removed from the throttle linkages.
Last edited by benz_guy; 02-02-2008 at 03:34 PM.
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#6
02-12-2008, 11:52 PM
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i replaced the cold start valve today, seemed to help the car is now idling normally in drive but still around 800-900 rpm in park. Also it does seem to intermittently idle at proper rpm sometimes. could there be a stuck valve somewhere? it really has me boggled, i think the car is possessed!!!! thinking maybe a bad temp sensor? when u guys say a dud temp sensor, do you mean the engine temp sensor or the coolant temp sensor? thanx
Last edited by benz_guy; 02-13-2008 at 12:02 AM.
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