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Low idle when warm

Started by 200 hp, 29 July 2010, 03:20 PM

200 hp

The other topic about engine cutting out in traffic has made me ask about a similar problem I'm having. Keeping in mind my 350SE D-jet does not have a tachometer, it's difficult to tell what the revs are at.

Anyway, when very warm in drive, the car would sound like it's idling very low to the point I can feel occasional vibrations and occasional un-smooth idle. Twice the car had cut out when in reverse, but only when the steering is in full lock. Say during parallel parking. When cold the engine sounds like it's idling high but very smoothly. Could it be an ignition problem? Rich mixture?

oscar

I think the first thing I'd try is wait till the engine gets to operating temp when the low idle is present, then I'd adjust the warm air idle screw by turning it anitclockwise until the revs sound right.

Searching thru some old pics here's the warm air idle screw.  The AAV is the auxillar air valve/air slide.  It closes when the engine has fully warmed up (or I think when the coolant gets to 70degC).  It sounds like your engine could be starving for air so opening the warm air idle screw a bit will counter that.  You might find when it's cold though that the revs runaway a bit but it goes once warmed.


1973 350SE, my first & fave

200 hp

Thanks for the tip Oscar, I'll try that first. A shame I don't got a tachometer to use as reference, so I'll have to use the oil pressure gauge. Should be at about half way point ( number 2 ) when warmed up at idle or when in drive? I noticed today it dipped down to number 1 line when in reverse, just before the engine cut out.

oscar

Yeah, sounds normal.  Oil pressure will be at 3 most of the time whilst revving at anything other than idle.  When engine's hot and driving low speeds it wont reach 3.  Warm idle will see it between 1 and 2.  Cold idle will see it at 3.   No dramas there at all.  So long as it never drops below 1 or constantly stays around 1 whilst the engine's running under varying conditions, I wouldn't worry.   A good blip of the throttle should always take it to 3.
1973 350SE, my first & fave