C36 Rough Idle and EGR issue - PeachParts Mercedes-Benz Forum

holdontight · #1 11-28-2006, 08:47 PM

Hello all, first post from the newest member and proud new owner of an almost pristene 1996 C36 with 88K miles. I bought this car a month ago from a guy that could not make it run right. No power, CE light was on, hard starting and so on. He had the car listed at 13.5k and I talked him down to 6k...not a bad deal I think!

I replaced the MAF and all the power is back and it runs awesome everywhere but idle. I have checked the usual suspects, EGR valve, EGR tube at intake, O2 sensors, and a few others.

I searched and searched and found some great info on this site, but nothing to solve this issue. The 2 problems are exactly this: In the morning after the car sits, it starts right up and idles perfect. 5 mins later, the car stumbles at idle real bad. The other (and I suspect it is related to the first) is when the car is shut off and restarted within 20-30 mins, it starts right up... if I leave it for any longer than 20-30 mins, it cranks for 5-8 secs before it starts, but always starts.

During my troubleshooting, I measured vacuum at the egr valve and found that 5-8 in of vacuum holding the egr open half way. And that is exactly what is causing the rough idle. I tested the solenoids that control vacuum to the Secondary Air system and the EGR system and they open and close while bench testing.

SOOOOO, Finally, My question is, what sends a signal to these electrical solenoids that control air to the EGR? Like I said, when the car is warming up, there is no vacuum present to hold the EGR open, hence the good idle. However, the second I snap the throttle, 5-8 in of vacuum is present and messes up my idle. This is also accompanied by a P0400 and a P0411 CE light.

With all the knowledge that I have seen on this board, I hope someone can help out the newest member! Thanks so much in advance!! I am a former Ford and Acura mechanic and hope to share my experience with this car and contribute to this forum as it comes!

manny · #2 11-28-2006, 08:54 PM

First of all, welcome to this forum.
Secondly, just to clarify, I'm sure you mean 5 - 8 inches of vacuum ( not pounds ) ?
Sounds to me like a faulty checkvalve of some kind, that would prevent vacuum from bleeding off.
I'm sure somebody with more in-depth knowledge on your specific model will chime in.

holdontight · #3 11-28-2006, 09:00 PM

Thank you-and yes you are right. 5-8 inches of vacuum. Thanks for the correction.

ProV1 · #4 11-28-2006, 09:03 PM

hi there!

i have nowhere near the level of knowledge as you do, so most of what you were saying didn't make any sense to me, but my 97 E420 w/ 106k miles has the exact same prob: car runs perfect, no issues when first started, but the car has uneven idle and stumbles around when sitting at traffic lights. car never stalls though, and no CE lights. i'm sure as more miles are racked up, my prob will get worse.

lemme know what you find.

holdontight · #5 11-29-2006, 10:53 PM

C'mon guys, I know someone out there knows something about this. Now we have two members that could benfit from some information. Some one with a manual (which I will be getting as soon as I can find one) should be able to see what component controls the vacuum solenoids. THANKS!

manny · #6 11-29-2006, 11:21 PM

When you bench-tested the solenoids, did you check the bleed-off port ( 3 rd port on the solenoid ), to ensure the vacuum bleeds off to atmosphere when the solenoid de-energizes ?

holdontight · #7 11-30-2006, 10:09 AM

That is a great idea. I checked the bleed off port (the port on the bottom with the screen attached) and when the solenoid de-energizes, air is allowed to pass without restriction. I also just tested the blue little check valve in the line comming off of the intake that supplies vacuum to the solenoids-functions like it should. I also did a test without electrical power to the solenoids-they are staying closed like they should and not allowing air to pass without the solenoid being energized.

I have been driving the car for the past couple days with the vacuum line blocked to the EGR. It has been running good and the idle is perfect. There has also been no check engine lights, but I am sure it is a matter of time before it comes on again (very cold to day, 2 degrees F. this morning). Still trying to figure out why those solenoids are being powered up and staying energized when they are not supposed to....

ProV1 · #8 11-30-2006, 11:36 AM

Hi there, it's me again.

I'm having the same problems w/ my 97 E420; rough idle when sitting at lights, and occasionally need to crank for 3-4 seconds to fire her up. otherwise the car is running great.

i'm a n00b diy'er and been reading different forums. One thing i noticed is that these problems are very common and seem to occur on almost every MB model.

A few items seem to pop up most often, which are CPS, MAF, engine mounts, fuel pump, vacuum leak and oxygen sensor.

B/c my car doesn't have CE lights or show codes, I think i can rule out the MAF and O2 sensor. I think a new CPS (aka reference sensor) will take care of the long cranking problem, and possibly also the rough idle. If it doesn't, well the part is $55 and it needs to be replaced anyway so i wont feel so bad. Then I'll tackle the engine mounts. My car has original vacuum & air hoses but on inspection they still seem ok.

Let me know if u replace the CPS and if it works out for you. I'm having trouble removing mine.

holdontight · #9 11-30-2006, 08:34 PM

ProV1, have you checked you EGR system? I have my car idling and starting like a champ when the EGR valve is shut (by disconnecting the vacuum line) and not being held open by this mysterious vacuum presence. I am not sure, is there both a camshaft position sensor AND a crankshaft position sensor on these 104 engines? If so, the cam pos. sensor would be on the upper end of the motor and the crank pos. sensor would be towards the harmonic balancer/crank pulley I believe.

larry1963 · #10 12-11-2006, 10:16 PM

I have a 2000 E320. Bad idle. Where is the EGR located on my engine?

holdontight · #11 12-12-2006, 09:37 AM

Larry1963, I am not as familiar with the E320, but I believe that your EGR valve is located on the passengers side of the engine. It is a little flying saucer looking deal that will have a vacuum line running to the top of it, then a steel tube running from your exhaust manifold to the valve, then a steel tube running from the valve to the intake manifold.

holdontight · #12 12-12-2006, 09:42 AM

Just a quick update on my EGR vacuum problem, I recieved my WIS ASRA dvd's purchased from manuals unlimited and evidently, my WIS program does not have all the info that it should! I spoke with another member of another board and they had info in theirs that I did not have in mine! Has anyone ran across this before with the WIS system? I am not happy. I still need to find out what sends an electrical signal to these vacuum solenoids that is holding my EGR valve partial open before I have no hair left to pull out!!