I've got an early 1981 300SD (617.952-12-000555) with 250,000 miles which has a very slow idle when it is first cranked in the morning. It has gotten worse as the morning temp has dropped. Temps are getting into the low 40's these mornings. If I don't give it a little fuel when pulling out of the garage, the engine often dies. As soon as I reach the end of the street, the idle is normal. I do not have this problem when I crank later in the day. Every once in a while, I experience some hunting if I put the car in neutral. Acceleration is good at all operating temperatures.

Any ideas?

That is the nature of these engines. The 240Ds came with a idle adjustment knob that lets you turn up the idle a bit when the engine is cold. You could probably install one in your car, but it would require some drilling of the dash. About the only thing you can do is turn up the idle a bit or just warm the car up for a minuet or so before you drive away.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

My 300TD has an idle adjustment on it as well. It looks like a plastic key sticking out of dash just to the left of the steering column.

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1980 300TD-China Blue/Blue MBTex-2nd Owner, 107K (Alt Blau) OBK #15
'06 Chevy Tahoe Z71 (for the wife & 4 kids, current mule) '03 Honda Odyssey (son #1's ride, reluctantly) '99 GMC Suburban (255K+ miles, semi-retired mule) 21' SeaRay Seville (summer escape pod)

Your rack damper could be a liitle too far in as well.

Do you use a block heater?

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

I remember the manual idle adjusters quite well. I had a '73 220D and a pair of '78 300Ds. I guess I have gotten used to the 300SD not having a manual idle adjuster.

RRGrassi, you may have something with rack damper. I replaced the rack damper 10 years ago and a little adjustment may now be in order. The manual says, "...screw the damper in until the transverse engine vibrations are remedied." Do you think a little adjustment of the rack damper out might be the answer? I'll try it when the engine is cold since that is the condition where I have the idle speed problem.

Thanks.

Don't know what you mean by slow idle, please expound. Rack dampener may need some work, as you mentioned "hunting". My '83 had similar up and down idle, replaced rd, problem solved. An '81 is a turbo, right? I was told the turbos do not have the dash idle knob. Good luck.

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83 SD

84 CD

By slow idle, I mean it is in the 400-500 RPM range. Once warmed up, it is around 750 RPM. At 500 RPM, the engine will often stall if you have to turn the wheels. You are right the '81 300SD does not have the dash idle knob. They were the first year without that knob. You are right, the '81 is a turbo.

You have found out that 500 rpm is fine untill you put a load (turn wheel, engage A/C etc.) on the engine. 700 is normal. I suspect my '82 has compression issues, yet does not alter idle speed as engine warms up. I'll have to work on that. Hard starting? Checked GP's?

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83 SD

84 CD

You just found one quirk of diesels! however, you should let it idle for a couple of minutes at least when cold. If you don't have an engine block heater, consider putting one in! Phil may have one of these. I know diesel giant does!

toomanymbz, no hard starting at all - just bump the starter and she's going, even on the coldest day. GPs are good (checked them recently) and I have an updated Bosch GP relay with glow after starting.

Knightrider966, after breaking the second breaker bar without budging the block plug, I gave up on the blockheater.

You've got the starting bases covered, thumbs up on the relay. Have you owned this car long? Did you notice the engine temp when the idle comes up? What weight oil are you using? Vac is a real big deal with these cars, clogged lines, leaky rubber connections, proper plumbing, etc. yet can't put my finger on this problem. You may just have to wait for engine to get to temp. I'm trying to come up with what would change in the period of time you're dealing with... Metal expands as it warms up. Low, but smooth idle, right? Fred's fuel? Name brand stuff?

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83 SD

84 CD

Tom-
How long do you let your cold start engine idle before taking off?
I found there is a big difference taking off with 3 minute warm up, engine hesitates. 6-7 minute warm up= no hesitation, much smoother, never stalls.
Frankie

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Frankie
It never ends!
1985 300D Turbo 181K Anthracite grey, "SOPHIA"
1984 300 SD Turbo(sold)
2004 Subaru Forester XT,Cayenne red.

NO, NO, NO! Do not try to break out the original block heater!!!! Sorry, I should have said that earlier. The original will be frozen into place and trying to bust it loose could fracture your engine block! These were often put in with threadlocking compound and I've yet to hear of anyone getting one of these out successfully. Diesel Giant carries a engine block heater that fits in the lower return hose and they put in good pics of how to install it. If you engine stops hunting and the Idle is steady at warm up, then this is often common. I let mine idle for several minutes when cold and then drive away gently until I see about 50 to 60C and then all is fine.

toomany MBZ: I've owned the car 20 years. It has a good idle by the time I get out of my subdivision. The problem has only occurred recently. Using Delo 15W-40 oil. Vac system is up to par. I only use either QT or Flying J Diesel- all from high volume dealers.

Frankie: I've never had this idle problem before. I do recognize that the engine is older and that may be a factor.

Knightrider966: I gave up long ago trying to get the plug out of the engine block. I, too, had visions of damaging the block. I checked ot your recommendation on the heater mounted int he lower radiator hose. Diesel Giant is located only 20 miles east from where I live.

I have thew same issue. On top of this it takes a lot of cranking (sometimes over a minute) just to get started on cold mornings (below 30). I fear for my starter because of this. I replaced my glowplugs less than a month ago and have upgraded the relay last year. I back out my RD pin a lil about a week ago too with little results. I also lubed the linkage and that didn't help either. My feeling is that the last time i put in the glow plugs I noticed the wires from the relay to the plugs had very dry rotted insulation and right before the connection they were fraying a little bit. Perhaps I am not getting enough current to all the plugs? Where can I get a new set wires/harness for this? I will back the RD pin out a little bit more and report my findings.

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1983 300SD White with Grey interior