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1981 240D
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Discussion Starter · #1 ·
As opposed to the normal questions about cold start troubles, I was wondering how it should act when it's 60+ degrees. I got my 240D about 2 months ago, and since it was still winter I just attributed the smokey and rough startups to the colder weather. But now, even when I'm getting ready to leave work (which means the car's been driven during the day already and it's 65 degrees out) and I go to start it, it still carries on for a few minutes. It still smokes, still misses (almost violently), and just doesn't like to do much. After a minute of sitting and a couple minutes of easy driving, it smooths out and everything's fine.

I've already replaced the fuel filters, air filter, did a diesel purge, and adjusted the valves.

I'm pretty easy on it, and I still only see 25-26 mpg (I was expecting a little more out of a N/A engine). Could these things be related?

For now, my idle adjustment screw doesn't work because the piece that secures that cable to the throttle linkage busted and I'm waiting on that little part to come in. But when it was winter, I used it frequently and it seemed to help.

My idle seems a little low too. I don't have a tach but all the body panel shake quite a bit when it's idling. My haynes manual says that the idle adjustment can only be done with special tools and by a certified mech. Does anyone have experience with this on a 240D? I've seen some discussion about it with a 300 turbo, but the layout seems a bit different than mine.

By the way, my car is single owner (before me), 1981 with 168,000 seemingly pretty easy miles. No real signs of abuse or neglect.

Am I worrying about nothing??

By the way, I'm loving this car more and more each day. I've heard about this happening to w123 owners, but now I'm experiencing it myself. It's slow...very slow...but it's such a great car. I'm so happy I bought it.

Thanks all!!!
 

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1991 300 SE
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18,534 Posts
The smoking and missing may be due to a preglow problem, a check of the glow plugs may be in order. The smoke is unburned fuel in a not hot enough engine. The excessive shaking is due to the engine’s uneven warming. The miss is from the one or two cylinders with lower compression in conjunction with not being hot enough.

Due to the above conditions if the motor mounts are worn it can cause panel shaking. The shakes can also be caused by a worn rack dampener bolt in the IP. How hot does the engine get? Is the mileage mostly city? Highway? Combo? If a mix the mileage is not too bad if the engine is not getting hot enough, the hotter the engine the better the fuel mileage. Compression issues can also have an impact on mileage.
 

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1981 240D
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858 Posts
Discussion Starter · #3 ·
Thanks JDC

That's a good point about the glowplugs. I forgot to mention that I did check them via the procedure in the Haynes manual and all appear to be fine.

Usually, I drive about 15 minutes to work. 1/3 of that is city, and the other time is spent doing about 55 on a bypass. More or less, it's pretty mixed driving.

I have never checked compression...I suppose if I get the chance I should do that someday.
 

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1991 300 SE
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She may also benefit from a longish trip once a month, say two or three hours one way, to allow the engine to get nice and hot and stay that way for awhile.
 

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2007 S550
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Smallfence, that piece has been a reoccurring problem in my 240D for years. I finally just opened the hood and tweaked the linkage, its simple. Be careful as you have to do it with the engine running but just look at the metal throttle linkage and see where you can shorten the rod by screwing in the adjustment screw, adjust it and you can hear and feel the engine throttle up. Get to a point that the throttle is nice, (not too high, better to err on the side of caution) and you lock it down. This works fine for me but be advised that if the idle is set to high it can be a problem on icy roads in the winter time and an extra burden on the flex discs and drive train.

How did you do the diesel purge, disconnect the lines and suck it from the bottle?
 

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1981 240D
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858 Posts
Discussion Starter · #6 ·
Cyberbach, thanks for the tip about the throttle linkage...I'm going to check it out this weekend! Also appreciate your words of caution, that'll make me certain not to get the rpms too high

For the diesel purge, yes I did it via the method on dieselgiant's webpage...a big ol plastic bottle and two cans of L/M diesel purge I ordered from that place in Ca that's been mentioned on these forums (really good prices). Two cans seemed like excess as it took FOREVER to burn it all. Plus, I never really saw any smoke or noticed any indication that the purge was doing anything. I still can't really tell a difference.

Thanks again for your input
 

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1981 240D
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Discussion Starter · #7 ·
jdc1244a said:
The smoking and missing may be due to a preglow problem, a check of the glow plugs may be in order. The smoke is unburned fuel in a not hot enough engine. The excessive shaking is due to the engine’s uneven warming. The miss is from the one or two cylinders with lower compression in conjunction with not being hot enough.

Due to the above conditions if the motor mounts are worn it can cause panel shaking. The shakes can also be caused by a worn rack dampener bolt in the IP. How hot does the engine get? Is the mileage mostly city? Highway? Combo? If a mix the mileage is not too bad if the engine is not getting hot enough, the hotter the engine the better the fuel mileage. Compression issues can also have an impact on mileage.
just as a follow up:

I hope that I don't have a compression issue. I thought the whole problem was a bit strange as I got the car in the dead of winter and it didn't smoke and miss as bad when it was bitterly cold, but now that I've been driving it for a few months and it could be 70 degrees out it will carry on worse. ah well, it runs nice when warm.

But, I did want to follow up on the rack dampener bolt suggestion. I've tried looking on the website for performance products, autohaus az, and other places and can't find it listed anywhere. I'm not sure what my problem is, but does anyone know of a good place to get a new one?

Also, are changing motor mounts a big job?

Thanks again.
 

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1981 240D
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Discussion Starter · #8 ·
UPDATE:
I looked further into the rack dampening bolt...and it seems my 240D doesn't have one...so there goes that.
The last couple of days it's been 80+ degrees out. When I go to start it, it fires right up and keeps running with very little missing and a lot less shaking. I don't even need to turn up the idle screw for the first couple of minutes...it's very nice!
Does this mean anything to anybody to help narrow down why it would miss and carry on at 70 degrees or less?

I checked the glow plugs and they all work
I've done a diesel purge
I take it out every once in a while to "blow out all the carbon" on a long trip
I plan on changing the motor mounts and doing a compression check soon

Other than the compression check, is there any other thoughts?? I just haven't done it yet because I don't have the tools. If there's no other ideas...I'll just shut up until I get the compression checked :)
 
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