I found a listing for a '91 300D in the paper yesterday morning. I know these are somewhat rare (at least around here) so I jumped on it. Called the guy at 7:30 a.m. and was looking at the car by 8. Had a price negotiated by 8:15! I have looked at a whole bunch of 300D's (79-87) and a few 190's and they all had multiple problems. Bad paint, broken turbos, broken sunroofs, torn seats, etc.. Everything, and I mean everything worked on this car. When I saw the interior of this '91 my jaw dropped - it was nearly flawless, and BLACK. I have nothing against a tan interior but I prefer black. Love at first sight. Brought it home today:

http://motorheads.net/benz/DSC00177.JPG

Of course it's the 2.5 turbo, automatic. 203,000 miles. There are only a couple of minor issues with the car:

The headliner is sagging around and behind the sunroof. It's not too bad but I'd like to fix it as it's the only flaw in the otherwise perfect interior.

There is a light clunking noise coming from the left front when going over bumps. It can also be heard sometimes when turning the wheel left. I'm thinking it's the balljoint. I've read some posts about this job - if I attempt it I will be very careful with my fingers.

The idle speed is very low, around 600rpm. When coming to a stop, the idle speed will sometimes dip to just below 500rpm and the car shudders a bit. I found a post that said there was an idle adjust screw on the back of the IP - I guess I will go look for it. I will also be checking the motor mounts.

Finally, the car seems overly sluggish when I open the throttle at speed. It takes several seconds for the turbo to spool up. Is this normal? I have to plan lane changes waaaay in advance. It seems to spool up much more quickly from a dead stop. How do I find the ALDA on my car?

Looking forward to years of enjoyment (and learning) from my MB diesel. Thanks for any replies,

-Dave

Nice car--The 2.5 turbo is a great engine.

__________________
Anders

1995 E300
2015 VW TDI Sportwagen 15K
1977 240D (197K)
2002 Subaru Legacy L Wagon (115k) (Wife's)
Gone but not forgotten:
2005 Buick LeSabre
1998 C230
1984 300D
1983 240D
1981 300SD
1974 240D
1974 Fiat 124 Spider
1968 Triumph TR250

Congratulations! The W124 diesels are very nice cars. How much did you pay for it?

You can check the ball joint by pressing down on that corner of the car and listening for squeeking and by lifting the car and feeling for play in the wheel while grabbing it by the top and bottom. Also check the boots on both ball joints and if they are cracked or missing you'll need to lubricate the joints ASAP.

Idle speed is easily adjusted by that black knob close to the brake fluid reservoir. At least that's how it is on my 87 300D. I have mine set on the second highest setting.

I would mess with the ALDA only as a last resort. First examine the clear vacuum line that runs to it. If it's clogged it will inhibit proper operation of the turbo.

__________________
2004 VW Jetta TDI (manual)

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

Nice color combo! Sharp looking car! Welcome to the diesel forum!

__________________
Nate

1995 E420
1992 BMW 525i
1984 300D Turbo sold
1993 Volvo 244 sold
1995 Volvo 944T R.I.P!


"The details are not details. They make the product."
-Charles Eames

www.cbs.nu

Thanks for the welcome everyone. I looked around for the black knob to adjust idle speed but didn't find it. I honestly didn't expect to find it since I read some posts on this board which said it wasn't there on 91 models.

I found a clear vacuum line (very thin) but I don't know what the ALDA looks like. There are two rubber vacuum lines going from the turbo to a couple of canisters near the right fender, and from there across the front of the car to a device mounted on the front of the engine which also has a large line going to the brake booster. The only vacuum line I saw on the intake was rubber and immediately split several ways. I can see that it will take some time for me to learn what everything does.

The paint has some slightly faded spots - I just went out and applied a bit of Mothers #7 polish to a couple of the problem areas and the paint responded nicely. It's obvious that some of the $43,000 sticker price went into high quality paint (the car came with the original window sticker, but few other records).

-Dave

Oooh, thats pretty...

__________________
Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

I am not sure about the idle speed, but I am pretty sure that the idle speed is somewhat electronically governed on this engine.

The manual says for the 602.96 with automatic tranny idle speed should be 680 +/- 20 RPM. It also says if you disconnect the control, the idle speed should drop to 620 +/- 40 RPM. This control is located at the back of the injection pump and is labelled Y22 on the attached diagram. You should check to make sure that when you disconnect that, the RPM drops as it is supposed to. I haven't tested this myself but I haven't had an idle speed problem up to this point. Perhaps the connection is not being made for some reason or another. If that is working as it is supposed to.

In the second attached diagram, you can see a nut labelled 3a close up, also I labelled the Y22 connector on it. I believe it is if you slacken the nut 3a, the idle speed will increase.

For the ALDA .. In December I adjusted the ALDA on mine. It was virgin and now it has been turned out 1/2 turn, or maybe slightly more. The car is so much better, and you don't feel the turbo "kick in" anymore. It is smooth on the transition and doesn't all of a sudden have way more power at 2000 RPM. The car also shifts much more nicely out of first gear because now I am depressing the accelerator pedal less for the same amount of movement from a stop. It is very easy to get the ALDA out to adjust, you just need to pop the windshield washer reservoir up and out of the way (it just lifts up with a bit of jiggling), then you need a 27mm and 25mm wrench that are fairly thin (I think those are the sizes). I had to cut my 27mm boxend off so that it would fit in the space. Once it's out, it is very easy to adjust. It's directly underneath the intake manifold on top of the injection pump, and in the picture that's attached, I point out the hose that goes from the intake to the ALDA (and it should go through a switchover valve on the drivers side wheel well because your car is a 91. It's important to check all of this before you bother muddling with the ALDA. You need to make sure the fitting on the intake is clean and not blocking the boost signal. Also you need to make sure the hoses are clean and make sure the switchover valve isn't releasing all the pressure to the atmosphere. I believe the easiest way to do that is to try and blow through the hose and see if you notice the air coming out the switchover valve.

Another easy way to check this is to disconnect the hose at the ALDA, install a T in the line, hook it back up, and run the other part of the T to a pressure gauge in your car through the window. You will need a bit of hose for this, but it's easily done and then you can make sure the ALDA is getting the signal it should. This is how I tested mine, and I was getting 11-12 psi right at the ALDA. So, that's when it was time to adjust it.

The ALDA itself is near the back of the injection pump, and is a square shaped thing mounted on top of the IP with a big nut under it. It also will have a little black knob on the top if it has never been touched before. It should be easy to spot, just follow that line from the intake through the switchover valve and back to the ALDA. Actually, you can see the ALDA in the diagram with both Y22 and 3a written on it (not the one where I added Y22). It's just to the left of the 3a label.

Hope this helps.. It's a great car. I think I just broke 100,000 km on mine last week!

Attached Thumbnails

     

__________________
1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

Thanks for the great information - I will look at everything you suggested as soon as I get some free time. :-)

-Dave

On the driver's side of the false firewall, nearby the strut mount, you should see a black knob that says "ELR". This is the electronic control for the idle speed.

Nice car. I am envious. I almost bought a 124 diesel last year and now I could kick myself for passing on it. They seem to be going up in price.

I still can't find it. Here is a photo of the area in question - maybe someone else can identify the knob?

http://motorheads.net/benz/DSC00194.JPG

-Dave

Thank you, and I hope you're right. It is a fantasy of mine to drive a car that appreciates rather than depreciates. I have kicked myself on other deals in the past that I let slip by - the great thing is that if you search diligently, another deal will come along. Good luck finding yours!

-Dave

I pulled the plug and not only did the idle drop, but the engine nearly died. Much more than a 40rpm drop. Anyway, it's working. :-)

I did as you suggested and once the boost came up, it pegged my gauge at 11psi. Pegged it rather hard actually. The boost came up very slowly, however. After flooring the throttle, the boost would build with increasing speed until about 6psi at which point it would rapidly peg the gauge. Took maybe three seconds to reach max boost.

I also tried a stall test - floored it with the brake on and it stalled at 1500rpm and 2-3psi. Normal?

Next on the to-do list will be the ALDA adjustment, I guess.

Thanks again for your helpful post, dataiv.

-Dave

I adjusted the ALDA out 3/4 turn. There was a cap over the adjustment screw that I had to basically destroy - felt like a hack job. :-) The lag off the line seems to be reduced somewhat, but it's not a huge difference. I may go back in and try another 1/2 turn.

Filled up for the first time today, just over 1/4 showing on the gauge, 340 miles. Put in about 13.4 gallons which comes out to about 26mpg (US gallon). A bit lower than I had hoped, but then I have driven it rather hard. I paid $2.24/gallon, btw. Overall a satisfactory experience at the pump - my driving cost is back to well under 10 cents per mile - nice.

I found another problem with the car - when it sits for a few days, there will be a puddle of diesel underneath the engine. The funny thing is that if it just sits overnight, it will leak nothing (or nearly nothing). That's why I never noticed it until now. I plan on putting the car up on ramps this weekend, pulling off all of the panels and figuring out where it's coming from.

I'm ready to do my first oil change. I have read a lot on this board about what oil to use and I am either going to go with Rotella-T synthetic or the Mobil-1 5W40 SUV. I have close to 250,000 miles experience with Mobil-1 in other vehicles and as far as I'm concerned it is a top-notch quality oil, but the bargain price of the Rotella has me wavering. It will probably come down to the mood I'm in when I'm in the store.

Thanks again to everyone on the board that has taken time to answer my questions, including ones I haven't asked yet (in the archives). Great forum - I hope to be around here for a long time.

-Dave

With my 91 300D I adjusted the ALDA out just over 1/2 a turn and it made a huge difference. I guess it depends on how tired the spring in the IP is, though... Definitely want to find out where that diesel is coming from, because you should be getting better mileage than that if it was highway driving.

I've noticed a huge difference in mileage now that I've taken the snow tires off. I expect another welcome increase in mileage once the winter diesel disappears, hopefully in the next month or so.

I am planning on replacing the K1 spring in the transmission this summer, along with checking the timing chain, and IP timing. That's what's on the schedule for my car in the next few months.

I forgot to mention earlier, but I am using Mobil-1 15W50 Synthetic in the engine, and Mobil-1 Synthetic ATF (don't remember the exact name) in the tranny. No problems with either.

__________________
1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)