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sprinkles08, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 23117
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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I've got a 2006 E320 diesel with about 260,000 miles on it.

Customer Question

I've got a 2006 E320 diesel with about 260,000 miles on it. It has a rough idle, but runs smoothly off-idle. I had similar problems in the past and took it to several dealers in the past for inspection. They were happy to replace many hundreds of dollars of parts in hopes of correcting the problem without any positive results. I found out that if their computer doesn't tell them what the problem is - they have no diagnostic experience to figure it out. Their guess was as good as mine. It turned out to be diesel from a certain filling station.
JA: Sometimes things that you think will be really complicated end up being easy to fix with a Mercedes. The Mercedes Mechanic I'm going to connect you with knows all the tricks and shortcuts. Are you hoping to fix this yourself?
Customer: As long as it is screwed to the engine without requiring any special tools or micrometers, yes. If I have to deal with timing, valves, etc, then I'll take it in. I also have to be concerned that if it is a fuel injector - and have to replace all 6 I will likely double the value of the car. May not be worth it. If it constitutes buying a single injector and slowly walking thru each injector position - I'm likely to do this myself.
JA: Is there anything else important you think the Mercedes Mechanic should know about your Mercedes?
Customer: I took apart the air inlet piping from the cleaner to the turbo. There was a puddle of oil in the bottom of the pipe. It had come from the PCV? system - not the turbo. I have no idea if this is normal and should be replaced. I am planning on taking apart the rest of the intake manifold and cleaning the oil from it if it will help or solve any problems.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Mercedes
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

The most likely cause for a rough idle is definitely a fuel injector. Outside of something such as an EGR valve sticking open or fuel quality, there is little that will affect cylinder performance on a diesel besides compression and injectors.

Physically replacing the injectors may be something you can do on your own but a scan tool is needed to program their classification codes before the engine is ran.

The first step in diagnosing the problem is to see if any fault codes are setting. Have you checked for codes?