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EVAP vent valve under hood

Tiny
MIKE ALABAMA
  • MEMBER
  • 1998 MERCEDES BENZ SLK230
  • 2.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 98,001 MILES
On a trip home from Florida to Georgia the car started acting weird as if it wanted to stall and as I was watching the RPM/s. I indeed noticed at idle in park the RPM's would drop almost to the stall point and then suddenly surge back up to around 1,000 RPM and then level back off to around 600 to 700 RPM and then the car would suddenly start doing the same thing over and over again until I disconnected the vent valve solenoid under the hood. I'm at a loss as to where to begin with this. I tried to watch the fuel trims and the MAF sensor and I do notice that the fuel trims went into the - negative double digits and when I pulled the plug on the vent valve solenoid again the fuel trims went back to around 0.0 for the short term but I'm still at a loss as to where to start. So for now I'm driving the vehicle with the vent valve solenoid disconnected. Any ideas would be greatly appreciated!
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Sunday, March 24th, 2019 AT 2:38 PM

6 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Welcome to 2CarPros.

If the fuel trims are showing negative, the computer is trying to compensate by adding fuel. Thus, it sounds like the vent valve solenoid has failed and sticks open when connected or is damaged internally and allowing a vacuum leak to occur. I attached a picture of the vent valve to confirm that we are talking of the same part.

Also, check to confirm that none of the vacuum lines which attach to this part are damaged, dry rotted, disconnected and so on. To me, it sounds like the part is bad and causing a vacuum leak when it is connected. However, there are other hoses and components that can be leaking.

Here is a list of components related to the valve and correlate with the picture I attached:

Vent Valve, Design

imageOpen In New TabZoom/Print

1 Compression spring
2 Valve housing
3 Spring cup
4 Bleed valve
5 Valve plate
6 Air admission valve
7 Connection
76 Vent valve
A Connection to activated charcoal canister
B Connection to fuel tank

Let me know what you find.

Take care,
Joe
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Sunday, March 24th, 2019 AT 5:06 PM
Tiny
MIKE ALABAMA
  • MEMBER
  • 5 POSTS
Yes, that vent valve is what I was referring to. I know there's also a purge valve but that's in the rear behind the wheel. I checked all of the lines and hoses from the charcoal canister all the way back to the vent valve under the hood and I don't happen to see anything that looks bad or dry rotted and no disconnections anywhere. I think you're right that it probably is that vent valve under the hood because the car only acts up when I plug it back in. I'll turn the car off, plug the vent valve back in and then restart the car and it starts right up but in about twenty to thirty seconds it starts wanting to stall and I actually did smell unburned gas outside of the vehicle with the car door open and that's while I was looking at the fuel trims to see what they were doing while I was trying to look for a vacuum leak so you're like right on the money. So I'm going to remove the vent valve and test it out and see how that goes.
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Sunday, March 24th, 2019 AT 5:43 PM
Tiny
MIKE ALABAMA
  • MEMBER
  • 5 POSTS
This would be the vent (purge) valve solenoid I'm referring to under the hood. I think there's too many contradicting names for the valve and the purge valve. So this one will show which one I mean:

https://www.amazon.com/SKP-SKCP664-Purge-Valve/dp/B07NDX3TKL/ref=mp_s_a_1_1?_encoding=UTF8&qid=1553474992&s=automotive&sr=1-1&vehicle=1998-63-853-852--8-6-7-2271-1594-1-2-1721--1&vehicleName=1998+Mercedes-Benz+SLK230

By the way, driving the vehicle with the valve disconnected won't hurt anything will it?
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Sunday, March 24th, 2019 AT 5:50 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Welcome back.

I agree. Actually, there are just too many parts anymore. LOL

That looks like the part. If it hasn't already, it will set an EVAP code. Honestly, drive it if needed, but I would replace the valve as soon as you can.

Joe
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Sunday, March 24th, 2019 AT 7:02 PM
Tiny
MIKE ALABAMA
  • MEMBER
  • 5 POSTS
Thanks for the reply and help Joe! Have a great week!
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Sunday, March 24th, 2019 AT 7:45 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
You are very welcome. Come back anytime.

Take care,
Joe
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Monday, March 25th, 2019 AT 6:16 PM

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