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1996 E300 Diesel, Shaky Idle Help please!

8K views 19 replies 7 participants last post by  nathanevans 
#1 ·
I own a 1996 E300 non-turbo diesel with 222,000 miles.

I've recently replaced the starter, water pump, injectors, fuel pump lines, glow plugs, and many other things.

The engine is in great condition. However, whenever the engine is cold and I start it up in the morning, I get a shaky idle with alot of smoke coming from the exhaust.

I've plugged in the OBD-II scanner and the only notable code I get is the P0120 throttle position sensor "A" circuit malfunction.

When the engine warms up, the problem goes away.

What's the problem? How do i fix it? Any help will be greatly appreciated.

Thanks
 
#4 ·
The shaky/cold and black smoke coupled with a faulty TPS is telling you that more fuel than required is being added for the event, ie a cold start.

I believe that if you correct the faulty TPS you will return to a smooth cold start. Good Luck
So based on both of your replies, I should clean/fix my TPS. Just to clarify, that is the cylinder-like black piece with a spring mechanism located at the top right under the hood correct? Also, what method should I use to clean it? And if cleaning it does not solve the problem, how could I diagnose exactly what the problem is?


P.S. - Tirona, I have no carbon buildup, at least in my intake system, as I bypassed the EGR and blasted the manifolds clean.
 
#7 · (Edited)
For the starters this engine has NO THROTTLE and the code applies to PEDAL position sensor. This is the potentiometer in front of brake booster. Pretty darn expensive potentiometer, but if the code comes back , you will have to get a new one. When the errors get bigger the CEL will come on and the engine will run in safe mode with about 50% of power.
Smoke and bad idle on cold engine can be from a glow plug, or 2 not working, or air in the fuel lines. Should not take long to check those things.
 
#9 ·
There is no air in the lines, I've replaced ALL of the glow plugs 8,000 miles ago. The potentiometer is what it must be.

I've had a different 96' E300 with the same error code, and eventually the problem escalated so much that the engine's idle would be so rough it noticeably shook the car and stalled out.

Just to clarify, this is the part I believe i need to replace:



Is this the correct part?
Also, here's the link to the page I got it from:

Sensor, accelerator position Mercedes, Puch from Bosch - 0 205 001 029
 
#10 ·
Yes, this is Pedal Position Sensor and I remember paying about $240 for one about 5 years ago. I did have that PPS triggering CEL, but don't recall problems with the idle at the time.
Still if that thing have repeated codes, you need to replace it and go from there.
 
#15 ·
Hey guys, I'm afraid my problem has escalated. This morning on my way to school my engine died out...I started it up (28 degrees out) and it ran fine for about 5 minutes and then as I was doing about 30 mph the engine lost all power and stalled out. I pulled over and opened the hood and the fuel lines did have bubbles in them. I got back in the car and it took me a couple engine cranks to get it going again and from there it ran just fine. How do I remove bubbles in the lines?
Also, as the engine was dying, I got two notifications on the little HUD on the speedometer. One said "BATTERY CHARGE" and displayed a picture of a battery in red, and the other said "ETS ELECTRONIC STABILITY CONTROL" in yellow. After I got the engine running again they dissappeared.

What are your thoughts on my problem?
 
#16 ·
You don't remove air bubbles from the fuel lines >>> you don't let them enter.
Check stickies for replacing fuel lines AND SOV oring.
The lights just indicated low car voltage - normal with dying engine. I would not worry about them unless they come back in different situation.
 
#18 ·
On fuel system working on VACUUM, the leaky orings let the air in.
Sounds like you didn't replace all aging orings, or did something wrong. Try to observe where the bubbles start. We do have fuel routing posted somewhere.
When I work on my system -a set of tubings with orings cost about $70. Not that expensive to get whole new set.
 
#19 ·
The bubbles are caused by air getting sucked in where it should be sealed. Finding the cause can drive you nuts but the main culprits are the SOV O ring or the pre-filter O ring. You stated you changed all the fuel lines, did you mean all the clear lines? or all the fuel lines? This is a low pressure fuel system so leaks sometimes just dont spring out. Example I recently had a air leak problem as well, the black rubber fuel line that connects to the pre-filter and runs all the way to the back of the fire wall (this is the fuel line that comes from the tank) was wet underneath so I replaced. After that leak was sealed a new one starting leaking immediately from the SOV, so I replaced the seal but it turned out to be bad SOV unit. Low pressure systems = hard to find air leaks in some cases, other times the lines are wet making it easy.
 
#20 ·
Check the fuel lines for leaks to remove air bubbles. You may need to do a little cleaning to determine exactly where the leak is occurring (and letting in air).

The other electrical problems may be caused by a weak battery. I would get that checked out. FYI -- I've gone to Advance Auto to check out my battery, they said it was fine, but I later found out the battery was defective. My point is to scrutinize or get a second opinion...
 
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