idle surge 84 300td

[BillyT]

I did some searching but didn't come up with a post that really matched what I have happening. I've noticed this a couple of times recently. I go out and start the car for my wife and daughter in the morning and let it warm up some for five minutes. Many times I'm outside doing something around the car. Twice recenently they have been running a little bit late getting out the door and it seems like maybe ten minutes passes by before they are ready to leave.

I noticed the idle gradually increasing a lot, like 2000 + rpm, and not sure if it would level out or not b/c I jump in the car and put the car in reverse to see if the idle levels out and it does while in gear. If I go back to park it's fine for a minute and starts picking back up again.

It''s only happened a couple of times and only when the car is left idling for ten minutes of so. Does this sound like a Rack Dampner Pin issue or? Around town, when warmed up and in Drive- it idles great.

Thanks for the help!

[jt20]

if there is not enough play in the linkages (in the right spots) , this could happen. Certain pieces of metal expand and put pressure on the throttle lever.

But I think thats unlikely considering the nature of this issue. you just started noticing yours without a pre-cursor, right?

I am going to suggest that you NOT warm the engine up by idling. You could be causing a runaway condition. Search "diesel runaway".

If you insist on a warm up period, run the engine over 1000 rpms.. preferably 1500 for at least 15 seconds before idling.

What is your oil consumption like?

[layback40]

we need more ifo about your car. How many miles? Much blow by? can you control the problem by use of the throttle?

[Diesel911]

Is your Oil level dropping over what you feel is a short period of time?

Perhaps after the Engine is hot Oil is getting past the Intake Valve seals and the Engine is runing on that Oil?
At idles speeds there is no pressure in the intake manifold as the Turbo is not pressurizing it.

Another factor is the Engine will use the Blow By vapor as Fuel if there is enough. (When you first start your Engine the oil pressure is high enough that the Oil Nozzles spray up into the Pistons; perhaps providing a better seal. As the oil heats up the idle Oil pressure drops below the setting of the little spring loaded valves in the Oil Nozzles and it does not spray any Oil at idle; perhaps this allows more blow-by due to having less Oil to help seal.)

[BillyT]

Thanks for the replies. I have 190k on the odometer and have only owned the car for five months. I haven't done much to it- changed fluids, fixed oil leaks, adjusted idle, rack dampner and put new rubbers under the air filter housing, etc.

The car has blow by. I'm not sure how to measure how much but there is always a light coating of oil around the oil filler cap. I add on average about 1/2 pint of oil and drive about 400 miles a week.

On cold start up I have to give it some fuel for 5/10 seconds or runs rough like it's being starved. I haven't done a compression check yet but I bet I'm low on a cylinder.

Thanks for the help. I enjoy working on cars but don't know a whole lot especially on MB diesels---yet.

thanks

[MBZ123]

Originally Posted by BillyT

Thanks for the replies. I have 190k on the odometer and have only owned the car for five months. I haven't done much to it- changed fluids, fixed oil leaks, adjusted idle, rack dampner and put new rubbers under the air filter housing, etc.

The car has blow by. I'm not sure how to measure how much but there is always a light coating of oil around the oil filler cap. I add on average about 1/2 pint of oil and drive about 400 miles a week.

Not bad on oil loss, you may find that most of this oil you're replacing is actually leaking out in drip form as opposed to being pulled into the combust proces. You just haven't tracked down the location yet. That amount won't show obvious signs in the form of polluted lakes in your driveway. The seepage atop the valve cover is due to a worn gasket in the filler cap. Replace with new to solve. Oh, cruise over to youtube to have a looksee on what some consider excessive blow-by. Frankly, just about every diesel, not freshly overhauled, in these cars will have some amount. What prompted the rack damper replace? Not too knowledgeable on this procedure myself, but sure it will come along soon enough.

Originally Posted by BillyT

On cold start up I have to give it some fuel for 5/10 seconds or runs rough like it's being starved. I haven't done a compression check yet but I bet I'm low on a cylinder.

Thanks for the help. I enjoy working on cars but don't know a whole lot especially on MB diesels---yet.

thanks

Do a glow plug test for this problem. Most likely culprit and a quick and easy learn. A multimeter is the preferred catalyst here. Had the same symptoms and bad plugs was the case for me. One of the first projects to initiate me into this disease, errr, obsession.

FNHB

[markg612]

Originally Posted by MBZ123

Do a glow plug test for this problem. Most likely culprit and a quick and easy learn. A multimeter is the preferred catalyst here. Had the same symptoms and bad plugs was the case for me. One of the first projects to initiate me into this disease, errr, obsession.

FNHB

I second that!

[BillyT]

Thanks- will check the glowpugs. The oil loss/consumption is minimal and I expect some blow by- I've just never known how much to expect. I had an old 59 Fordson Dexta tractor- 3 cyl. perkins diesel- that had blow by to the point is started passing oil through the rings, I think, and oil actually was coming out the exaust. I parked it. Wanted to keep it ( and the parts 59 dexta) for a rebuild project but the wife made me lose it in order to get a newer one. I agreed sorta.

I only adjusted the rack dampner pin because my warm idle was low and increased it just enough make the engine run more smoothly. If you have the old rack dampner pin, not gold colored, some say you should replace it if your experiencing warm idle issues and don't seem to get any results from adjusting your old one. It's only what I've read- I'm definitely no expert/mechanic. The new pin is like $50 for this little spring loaded adjusting screw.

Thanks again for the help.

[okyoureabeast]

Check your linkages. Have someone press on the go pedal and see if you have any play.

Also check to make sure none of them are sticking. I betcha simply sticking some ATF inthere will end the problem.