It seems that rough idle in our cars seems to be an issue that is always around and several factors contribute to this aggravating situation.. Finally I resolved this issue and I owe it to this forum and the help of Mr. Jim Forgione.

After replacing both distributor caps and rotors, plugs and coils, air filter and cleaning the MAS, the rough idle persisted. Hmmm, back to the drawing board...

Two weeks later I replaced the IAT which was shot..no improvement...

Then one Sunday I got down and replaced the fuel filter which was unbelievably dirty/plugged. Then I tested and replaced the O2 sensor using the technique found in http://www.w124-zone.com/articles.php?article_id=27 . Word of advise..it is not a simple task to get to that sensor, the exhaust needs to be dropped on a M119. (if someone knows of a faster way, please post it because it will surely save another member a lot of time and energy and patience..).

I started the car afterwards and the idle seemed to have improved a bit but I was not top-notch.

By the end of the day I began chasing for vacuum leaks..(yes I know..I should have done that from the very beginning but I hadn't had time to stop by Sears for a mity vac until that previous Saturday.. All lines were holding OK until I hit this 1 to 3 rubber connector shown below. There is a line coming in from the engine which splits into 3.



The lines were practically sliding in and out. So I rigged it with some tie-straps. Then I started the car, stood back..Ain't that some sh$@... The idle leveled out nicely..I jumped in, took it for a ride and yep...that took care of it, in P/N or D... After that I went to the stealer to order a new one which I am waiting for..It was $15.10. I will post the part number when I pick it up. Now if someone has any insight as to why this little part was the catalyst for a rough idle, please enlighten me. I am still trying to locate this rubber part in the EPC and service manual with no success and the guy at service was not very helpful about it..as usual.. From what I have chased I believe that the solenoid to the right is part of the AT, but what are the two yellow check valves..still trying to figure it out...

Now I have to figure out the tapping noise on the drivers side engine bank a shift issue that is more of a nuisance than a problem and only acts up when I floor the car or demand performance...I am attributing it to the kickdown switch at the moment but I will let you know when I have solved it as well..

Thanks a lot to everyone,

Cheers,

DH

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"The bitterness of poor quality remains, long after the sweetness of low price is gone..http://www.peachparts.com/shopforum/...milies/eek.gif

Could it be a 3-way check valve for climate control?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

amazing find, that's something. I'm going to try this in my 94 E420 tomorrow and post the results. what was the part number you ordered ? thanks...

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Whether you think you can or cannot, Either way you're right!. by Henry Ford.

It is a vacuum check valve, but I can't find the part # for the rubber harness. Maybe it's a dealer only item. The valve is under Fast Lane, check part # w0133-1638684

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1994@@1994&makeid=63@@MERCEDES+BENZ@@X&modelid=6396%3AED|10000072%3AMBC|1530@@E420&keyword=vacuum+valve@@vacuum+valve&catid=All@@All&subcatid=P%3A241861@@Vacuum+Check+Valve&applicationid=W0133-1638684@@Vacuum%20Check%20Valve&mode=PA

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I scoured the epc for an hour and I couldn't find the 1-to-3 rubber connector. If you find the part number, please post it here.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles