1999 E320 3.2L V6 Rough/Poor idle condition - PeachParts Mercedes-Benz Forum

sumday · #1 10-18-2006, 06:12 PM

I am working on a 99 E320 with a 166,000 miles and a 3.2L V6. the problem I am having is only at an idle, mainly when the vehicle is in gear at a stop, otherwise the car seems to run fine while going down the road. The check engine light was on when I first started to look at the car and I pulled codes to find a P0300, P0302, P0304, I had replaced the plugs and wires on the according cylinders(Cyl 2&4) with no change. I have been told that the plugs were changed less than a year ago, and I know that doesnt mean they are good, but they appear to be oe style plugs and I would not expect them to be causing a running condition due to how well the car runs off idle. I am also wondering, what is reason there are two plugs per cyl, are they there for emission reasons? well any help would be greatly appreciated,thanks. I have already cleaned the MAF with no change in the running condition. Also as I have been running further checks on the car I have found that i may have a leaking fuel injector/injectors. Fuel pressure checks good, but I am losing pressure at rest after I pressurize the system and close off the rail from the rest of the system(this is done by having a shut off valve between the rail and the feed line and closing the valve after pressurizing the system) I will lose almost all pressure after an hour or so. Due to the fact there is no return line on the rail the loss must be through an injector/injectors, but as I am watching data on the scan tool I dont see a fuel correction for a possible problem. I do have a long term fuel correction of 10 on the left bank and I have not been able to duplicate any codes that were in the vehicle to start with. I am wondering if I may have a vacuum leak somewhere or maybe an EGR issue. I have very little experience with mercedes cars so I am not to sure where to go with this

Qamar · #2 10-19-2006, 02:14 AM

Check out the air filter. I have 95 E320 and had the same problem in idol. Well at last I found that the air filter was the main culprit.
Secondly disconnect your car MAF from the air filter. Start the engine and ask someone to sit on the wheel and rev the engine to 2000 RPM. Slowly and steadily spray any carburetor cleaner or a brake cleaner inside the MAF window. This will thoroughly clear any dust accumulated on the MAF sensor and will also clear the throttle body. You will be amazed to see the smoothness of the engine. Don’t spray too much. While you are spraying the carburetor cleaner inside the MAP the car engine will sputter, don’t worry nothing will happen. Where ever you feel that the engine is dying stop the spray and then again start the spaying, till that time you feel that the idol condition has improved.
Do let us know about the progress.

#3 10-19-2006, 07:23 AM

Use only OEM plugs and wires, the aftermarket stuff will cause problems.

As for cleaning the MAF, IMHO, the use of carb cleaner might melt delicate parts and it leaves a residue.

blackmercedes · #4 10-19-2006, 09:12 AM

I have heard that a failing AMM can cause a misfire code, but I think it's usually accompanied with a fuel trim code.

While you have the car on SDS, check the fuel trim adaptation values to rule out the AMM before replacing it. BTW, 95 and 99 diagnostic systems are very different, so what a 95 owner found and what might work for your car could be quite different. (95 has M104 and 99 has M112 for starters, many differences after that...)

I know the M112's have a crank sensor problem, but I can't recall the symptoms. Have you done a search on "M112 problems" ?

sumday · #5 10-19-2006, 12:56 PM

While going over the car a little further and not finding anything real concrete, I decided to look at the EGR system and I found that the EGR tube was very hot and the car had not been driven yet so this was only from 3 to 5 minutes sitting at an idle, which leads me to believe EGR is flowing at idle. I wanted to take it a little further by disconnecting the vacuum line between the EGR valve and the vacuum transducer and the idle went smooth, plug it back in and it goes rough. My question is, since I know how the germans need to be different than everyone else, Should the EGR be flowing at idle ? I would think not , but I'm not sure how mercedes regulates this...

david s poole · #6 10-19-2006, 03:01 PM

the egr is very definately not supposed to be running at idle you have found your problem.