Hey everyone,

i'm having some issues with my 4.5, after i have been driving the car for a some what extended period of time 30-45 minutes+ the car will shut off as soon as it hits idle.

the motor can heat up fine in the first 20 minutes (according to the temp gauge) or so and i will have no issues. after the extended period of time she's still not in the red zone but just starts shutting at red lights. all the traits are very similar to vapor lock on warm start issue, but i have never had this happen while driving.

weird thing is, if i put it in neutral at the light she won't shut off. as soon as i put it back in drive if i don't give it gas she shuts right off.

any thoughts?

thanks

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W211 '03 E320 | W108 '72 280SEL 4.5

http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg

You could try increasing the idle rpm. When cold, this should be as high as about 1200rpm and then gradually decrease. Try to keep it at at least 600rpm when fully warmed up.

Sometimes the AAV needs attention. If it does not move smoothly, you can have it stick and then when car gets fully warm, it lets go and closes causing rpm to drop. This makes idle adjustment difficult.

You could try cleaning AAV by soaking in Carb cleaner and then perhaps something like Simple Green. Ultrasonic bath would help, if you have access to one. You can take the AAV apart, but that would be a last resort. New ones cost an arm & a leg. But perhaps getting a used spare and trying freeing it up might be worth while.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The AAV i assume is where I adjust the RPM? If so its def smooth and easy to adjust the RPM. I've adjust it a couple times now, someone else mentioned i should try raising the RPM but I was a little scared to run it too high so I believe I have only adjusted it up 1.5 turns. You think it just needs some idle attention? I can def keep messing with it there if need be

The idle fuel and idle air are controlled by two separate adjustments. The injection pump arm and throttle arm should both be against their idle stops; this means the linkage plays no role in synchronizing idle fuel and idle air when the engine is idling in neutral. Therefore, it is necessary to synchronize the idle fuel and idle air manually. It is a repetitive, trial and error procedure.

The procedure basically involves adjusting the idle fuel setting, then adjusting the idle air valve for best idle, then checking idle speed to see if it’s correct. If it’s not correct, you try another idle fuel setting, readjust the idle air for best idle, and recheck idle speed. This procedure is repeated until best idle and correct idle speed are achieved.

Note: Before adjusting the idle, all other aspects of engine operation should be as perfect as possible: points and timing properly set, good plugs, valves properly adjusted, no leakage at the Cold Start Valve or thermostatic warm up system, linkage properly adjusted and the throttle valve must be fully closed.

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Britton McIntyre

68 280 SE coupe 'Hairball'
70 280 SL
71 280 SEL - RIP May 2010

I think you must be talking about a different injection system. I assumed that the 108 with 4.5 engine is an M117 4.5L with Djetronic electronic injection. No idle fuel adjustment or injection pump.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The AAV is the auxiliary air valve. It is a thermostatic valve that air passes through when engine is warming up. It eventually closes when engine coolant is at about 150F. There is no adjustment.

There is also an idle screw that adjusts the amount of air that enters the engine when the throttle plate is closed (i.e. at idle). You use that to adjust idle speed.

Both are shown in this picture:

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

ahhh... ok i have only adjusted the idle screw

if the valve is stuck open or closed and is causing it to stall wouldn't it do the same when it was in neutral?

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W211 '03 E320 | W108 '72 280SEL 4.5

http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg

Sorry, I did not realize that some early Djets did not have a tachometer. Assuming you don't have one on dash, you will probably have to beg, borrow or buy a hand held tachometer.

Alternatively, get the engine well warmed up (go for a 20 mile drive with hills, stop, starts etc in warm weather). Then adjust the idle screw so engine is idling steadily, but not too fast. Then next time you start engine from cold, note how it idles. If engine rpm surges up and down, then you need to cut back on hot idle rpm a bit.

This assumes your AAV is working properly (and they seldom do if not cleaned).

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

crafty, Graham:

In addition to the idle air controls, it seems in order to suggest a bit of attention to the idle fuel control. The pulse width to the injectors is adjustable at idle by the mixture screw on the ECU.

Of equal importance is the voltage available at the injectors, which is a function of the condition of all the connectors and ground terminals. When the engine is at a low idle the output voltage of the charging system will drop, and when combined with accumulated corrosion on connectors and grounds can result in such a small signal to the injectors (already very short at idle), that an insufficient amount of fuel is injected to maintain idle speed under the load of an in-gear situation. In Neutral the load is removed, idle speed increases slightly, voltage rises, and injector pulse increases.

Additionally, fuel pressure should be at or slightly above design specification.

If the car is shutting down after a long run, or even a short one, but it runs fine while you are driving at a steady speed you need to do a compression check.

On these older cars that is a sure sign of lower compression. This could be something as simple as needing a valve adjustment or as complicated as a valve job.

But if you don't check the compression you will never know, and if you do, and it is within specs, then you can move on to the fuel system.

This could also be something as simple as a vac leak, so check all the ends of your vac lines for splitting and replace any line with a crack in it.

I missed your second sentence!

When you put car into drive, it puts an extra load on engine and rpms drop. I just went for a ride in my 350SL which has same engine. The difference between PorN and D is in the 100-150rpm range.

Let's say you set your car to idle in P at 700rpm when not fully warmed up and then go for a drive. If the AAV is sticky, once fully warmed up, your idle could drop to as low as 500rpm in P and then when you put it in D, it may drop to 400rpm (which usually means it will cut out unless you give it some gas).

As others have mentioned, there are many possibilities of what could be cause of your problem. But after owning a djet for 25+ years, I would always look first at the AAV for your symptoms.

You can try twiddling the idle knob on the ECU. Set it in middle of range (I think that is 9 clicks from either end of range?) Then try 1 click at a time either way with a burst of revs in between. This screw adjusts the idle mixture but is just a fine tuning. I think it had more to do with meeting environmental regulations than anything. You need an exhaust analyzer to set it to factory specs. But worth a try to see if affects anything.

BTW, this 107 link applies to the 4.5L Djet - might be worth reading. http://www.benzworld.org/forums/r-c107-sl-slc-class/1600137-comprehensive-illustrated-djet-72-75-350-a.html

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

If it is your aux air valve then use caution when buying a replacement. There are two styles, and early and a late, although I think the later style was used for the K-Jetronic.

Still, some sellers don't know the difference so make sure you do. They look a bit alike but are different enough that when you see them you can easily tell them apart.

thanks so much for the updates!

i'll admit i don't really know what i'm doing when it comes to this car so all this info is very helpful.

update, i turned the idle speed screw about 2.5 turns up. it doesn't feel like it's idling super high (honestly i can't tell the difference) and it seems to have cured (knocks on wood) it dying while it's warmed up. As far as the knob on the ecu, i have made some small adjustments there before but i did not know it had to be on and i need to give it some gas in between knob turns. any chance i could have cause any harm?

i'm going to look at removing the valve and giving it a cleaning as stated and and re-check the how it runs. it's been around 110 all week so it def heats up and i haven't really been driving the car because of this issue.

thanks again everyone!

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W211 '03 E320 | W108 '72 280SEL 4.5

http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg

so i pulled the valve off, it's not looking like it's in too good of shape

i have it soaking right now, so i'll see if it'll help any but i'm not too confident

any leads where i can get a new one? gasket is totally toast as well

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W211 '03 E320 | W108 '72 280SEL 4.5

http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg

She works! ...i didn't check t see if was working before though. i did;t think of doing that until after i cleaned it

hopefully this fixes the issue if not i'll report back.

thanks again everyone

__________________
W211 '03 E320 | W108 '72 280SEL 4.5

http://i66.photobucket.com/albums/h2...ps9b542eaa.jpg http://i66.photobucket.com/albums/h2...ps5723c50f.jpg