Hello all, I am the proud owner of a new to me 300D and over the last few weeks I have been going through the car and doing maintenance.

I am new to diesels so I was hoping for some help troubleshooting when I first start it is cold it idles rough but if I give some slight gas it smooths out....

How can I determine if it's the glow plugs or injectors, etc? I cleaned the engine bay and noticed no diesel leaks so far....

You should ask the moderator to move your post to the Diesel Discussion section. You'll get some ready answers. A lot of the diesel guys never look in the Tech section. BTW welcome to Peach Parts this is a great place.

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'89 260e (212K Mi.), '92 400e (208K Mi.), '92 400e (not a misprint) (146K Mi.), '95 C220, '81 240D--Sold

Sounds like it needs a valve adjustment. I used to have to keep my foot on the accelerator and speed backwards out of the garage, else it would die. Got a valve adjustment and resolved it.

If it's an '87 then it will have the self adjusting followers. My money is on glow plugs. Ohm them. Open is bad. Less then about an ohm and a half is usually good. A bench test will more adequately assess glow plug function, but I've never needed to bench test a glow plug.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

The 1986 and 1987 603 engines are somewhat cold blooded when the glow plug cycle actually stops. A rough initial cold idle is the common description of this.

I have never had one of these engines. If I wanted to prove the problem. Putting a heavy gauge feeder to the glow plugs and leaving them on for the first few minutes of operation would be the test. If the rough cold idle left then I might upgrade the system to an afterglow set up as the newer cars have.

If that test did nothing perhaps looking for air getting into the fuel system when the car sits around might be my next step.

The idle speed is adjustable with a control somewhere near the firewall I believe as well. You might be set up a little slow making it even a little worse than it normally is.

All owners of these mention what you claim as well I believe. Hard to say if yours is worse than normal. Basically engine starts clean and then the idle starts to roughen up.

Sounds like glow plug issues to me.

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Jim

Thank you for the feedback guys..... I'll start with the glow plugs then....

I have a 300 D, and just sold a 300 TD.
Rough idle is pretty normal for 30-45 seconds. It will remind you of a tractor when it first starts. If it starts with one glow cycle, the glow plugs are probably fine, and the warm up cycle is normal. When it is cold, two cycles help. (15 F and below)
Smoking is normal for this time, but goes away quickly.
I highly doubt any of your glow plugs are bad, as just one bad makes these very hard to start.

A little smoke when you floor it is normal too.
87 is a real mix of old and newer tech. Aluminum head, but purely mechanical.
Make sure your cooling system is in top notch shape, and so long as it never gets overheated, the 603 will serve you well.

Check the tensioner and spring carefully. It should be pretty much parallel to the engine block. If there is much of an angle on it at all, its time to replace it. The plastic tanks on the radiator get brittle with age.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes