Hello All,

My '75 300D (and other older MB diesels that I am familiar with) has a manual control on the dash for increasing the idle speed when the engine's cold. My newer '83 300SD has no such control, and it doesn't increase the idle speed on its own. Consequently, I have to sit in the '83 with my foot on the throttle until the engine temp gets up past 40°C so that it will idle relatively smoothly.

Proceding under the assumption that my '83 is not working properly, how is the fast idle supposed to be controlled -- internally on the injector pump perhaps? Is there any way for Joe Fixit to set it up right, or is this a job for an injection shop? The MB CD-ROM has been zero help, at least from what I could[n't] find.

Thanks much in advance!

Brett, in gray, foggy, dreary, northeast Orygun.

A number of things can affect the idle when cold. Injectors, fuel/air filters, Glow plugs, fuel problems, valve adjustment, engine wear...this just starts the list.
I would raise my warm idle speed to about 900 RPM's until I could root out the problem... this will help at start/warm-up time.

It has been very cold in Va. and with fuel additives and higher idle RPM...I have had no problems in my 84' SD.

__________________
1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car

Welcome Eastern Oregon...

What does your owners manual tell you about cold starting? If it has a reference like "push the accelerator to the floor/let up and then start" or something to that effect then you have some kind of internal mechanism that helps with cold starts.
One the other hand if it says to sit in the cold until the car heats up to 40 C then I'd get a stick the right length and prop the peddle at about the right rpms. I used to do this for years in my old BMW when I put a weber on it...

I do love the simplicity of the 115 body and all manual everything...

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Hey Dreadnaught,

I'm starting to believe that the later diesels without the idle-speed knob don't have a fast idle, though that doesn't make much sense and I could be wrong. Mine is one of the later models but I don't have a fast idle or at least it doesn't work if it's there. An 83 300SD that I recently tested didn't have it either. First thing I would do is test all the glow plugs with a ohmmeter and make sure they're in working order as even one bad glow plug will make a cold diesel idle very poorly. My glow plugs are apparently all fine, but I still get an occasional hiccup during cold idle if I don't keep my foot on the accelerator.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I had an '85 VW Jetta diesel which had a lever on the dash which advanced the timing, although I don't think it did anything with the idle speed. Then the lever was pulled out the car had a noticeably louder diesel knock to it.

On my current '84 300D I think its odd that on a cold start when its really cold out, maybe below 25 or 30 degrees, my car starts and idles with a very strange sound. It almost sounds like it is muffled, and more smooth and quite then the typical diesel clatter it has when it is warm. This only happens when its really cold out, so it almost makes me think that there is some kind of cold-startup system on these cars.

Any ideas?

Greg
'84 300D, 172k

Thanks for the replies!

Since the engine starts and performs fairly well [after initial warm up], I think I can shuffle a few of those items farther down the list...

Between your comments and from what I've been able to glean elsewhere, it looks like valve adjustment is a very likely candidate. Since I haven't even pulled the top off of the engine in the 4 years that I've owned the car, I'd say that at the very least, a check is overdue. Also, I hadn't really suspected glow plugs since it *starts* reasonably good, but I can see where they could still be a potential culprit.

I'll let you know what I find...

Greg, I know what you mean by that muffled sound after a cold start. My car does the same thing, but only before I press the accelerator. This may not be part of some cold start mechanism, maybe it's due to low engine speed and/or low thermal energy produced in the cylinders from the cold air. I just wonder if these cars are supposed to have a fast idle after a cold start. Anyone?

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

The owners manual does say to press the pedal to the floor and release when cold. Have to believe this either sets a fast idle or advances the pump timing. I have to say that I don't take alot of stock in the manual, I had a 80 300d with idle advance on the dash, the manual stated in temos below 32F press the pedal to the floor 2-3 times before starting. I have repaired truck diesels for years and have no idea what they think this does?

I cant believe you have to manually hold the idle up.