pskdude

Hello all. I have searched all the rough idle threads and mine had slightly different characteristics.

-Cleaned MAF sensor as instructed by other threads. mpg improved slightly but became worse again with time.
-Change all the o2 Sensors. I had a previous code of a short that now is gone.
fyi. I used the generic ones Bosch makes, The universal ones require you to attach both ends. But ended up working great! mpg at this point increased 3/5.

Now my issue is im still having the rough idle and on slow down the car seems like its going to turn off sometimes. What do you suggest i change next.
MAF or EGR Valve.

On another note I notice i waste wayyy more (10-12mpg) gas on idle than when im driving whether its city/high, could this be a sign its the MAF?
In other words I can be driving around town and im at 15mpg. Even with a heavy foot. At any point if i stop at a stoplight. It will continue to drop till it gets to about 12/10 :/

Any advice is appreciated!

btw here is the link i used for the o2 sensors.
http://amzn.com/B000BZG8ZU

Yidney

Not sure I'm following what you are saying about mpg at idle. I assume by idle you mean sitting still. When you are sitting still you are getting 0 mpg. You can run your tank dry and go nowhere - that is zero mpg. So I'm not sure what you are saying when you say at idle it drops to 10-12 mpg. If you are talking about the mpg average since you started you car that morning, of course it will drop as you sit still. The longer you sit the lower it will drop because it is averaging 0 with whatever you had before you stopped.


EDIT: But that doesn't mean it is using more gas at idle than driving. It is using way less gas per minute. But it is still 0 mpg.

pskdude

Ahhhh I seee! Thanks! Silly me I understand now. I assumed it would sit at what it measured last in mpg.

Any advice on what to change next ?

Rudeney

Where did you get the MAF sensor? Cheap aftermarket units rarely work well. I'd use only genuine MBZ or Bosch.

pskdude

@Rud. Havnt purchased any yet. Since i was planning on buying the OEM. My question was should I change the MAF or egr valve next? Seems like the 2 things that affect rough idle on the forums.

Rudeney

Here's a test- unplug the MAF sensor (it will probably trigger an MIL, but just ignore that). If the car urns worse, then it's probably not the MAF sensor. If there's no change, then replace it.

pskdude

sounds good! ill try it today and post the results.

pskdude

So I removed the MAF sensor and had the same exact rough idle. Going to take a shot and replace it with a bosch one. :/ 190 ouch!

pskdude

MAF sensor was replaced with a brand new one. STILL the same rough idle.
Going to take apart all the fuel lines and check the vacuums tomm. not sure what to do next.

pskdude

So after Checking almost every line under the hood i found several that were in bad shape. fixed. but The rough idle is still happening.

Seems after replacing o2 sensors, maf. im still doing about 12-13 mpg on average with a/c on. in the city, highway about 15-17. Does this sound normal ? And no i don't have a heavy foot. When i do it comes down to about 10-11. :/

My next step i Guess would be to change the EGR valve as per other posts.
Ill update as soon as I do.

seemayur

I had a similar issue and it ended up being a bad cam shaft position sensor. do you have access to an obdII code reader, you can borrow one from some of the auto parts stores. I hooked one up to my car and it threw a code that lead me to the cam shaft position sensor. I changed that out and it solved my problem.

pskdude

yes i have put the scanner to it. and no codes. :/ One of the first codes i received was o2 sensor short. Then I replaced and had no codes, now its clear.

pskdude

Thanks for all your help guys. It seems im going to be getting rid of her. Been fun while it lasted. My longer work commute requires me to have a more economical car.... :/

johny1989

clean injectors

Eojj

Shame you had to get rid of her. I was just going to say I drive a lot of city miles and my clk500 gets horrible mileage. Probably around 13-16mpg city driving. Highest I've seen was 22.5mpg driving on the highway.

pskdude

I know..=( especially after ive replaced almost every part that would go bad in the car after 100k miles. Full control arms/ all shocks/ all top hydraulics/motormounts/valvegaskets . etc. Not going to be appreciated as much by the next buyer.

pskdude

After a long battle with this issue I finally kept the car for weekend driving the resale was terrible in dealers. I took it to the shop and i got the following codes. (See Attached) Also he tells me that the loop is broken on my car or there is a short and he cant read codes from Command. (was trying to see if the injectors were the problem) Could the initial MAF short be the problem ? Going to start following the harness see what I can troubleshoot myself.

note: i was in the process of changing my stock radio and had it out. Will this affect the readings from the diagnostic tool ?

Rudeney

Is the MIL illuminated now? If not, those are just stored codes from where you unplugged the MAF sensor to test. I'd clear them, then drive a while and re-check.

DanielFD

just wondering, exactly how you fixed those vacuum lines? that vacuum line that you took a picture of in the picture it runs down and enters the intake manifold from the bottom.. worst part is that its connected inside of the manifold. its not a simple job maybe it wasn't done correctly? When vacuum lines leak they can give out all kinds of errors. my car was giving out EGR errors and it turned out to be the vacuum line that lead into the pressure sensor was broken. also you should checkout the vacuum lines connected to the EGR in the back and the ones in the front should be checked thoroughly especially in the places where they connect to something (their ends). it may not be apparent at first but moving the line around should help show cracks.

pskdude

Sounds good. I do not get any illuminations. Ill try and clear them and continue checking vacuum lines as Daniel suggested. The one i replaced had an ending to it. Might not be the same line you speak about. I will continue checking a little further into the EGR lines etc. Thanks for the help guys. Dying for her to run smooth already. any idea why my guy says the diagnostic tool isnt able to read anything or get any diagnostics. he had said something about the SAMS being in short or a loop not closing... :/

Rudeney

I'm not sure about the "SAMs" comment. Any generic OBDII scanner should be able to read and reset ECU codes. It's only when you get into the other systems (ESP, ABS, SRS, etc.) that you need special equipment that communicates over the car's CAN bus.

DanielFD

Problems like the once your car is experiencing require a lot of testing to figure out exactly whats going on. try to get to an independent shop that has STAR (Mercedes's own scanner solution). certain tests can be performed; even testing of vacuum lines. viewing live actual values and so on to pinpoint the problem your having.


Weird about the vacuum line. it took forever to realize it wasn't connected on the outside of the manifold. i didn't want to take the whole engine apart. My friend and I went through hell to fix that vacuum line. At first we were like oh that simple just remove the secondary air pump so we can reach it.. then ohh just remove all the front sensors to reach it. then ohh lets just remove the fuel rail to reach it. and then we realized we had taken apart half of the engine and the manifold was out haha we had started at 7pm finished at around 1am.. I guess I'm scared of that vacuum line

pskdude

this problem has been becoming worse and worse. I finally got a check engine light and decided to take the car in for service.

they did the vacuum smog/leak test and. Came up blank....no leaks....

The following Code came up and they want to charge me 800 bucks to change. They said it was the following (See below). Anyone ever had this issue ? suggestions ?

P2-075-002 Purge Control System slight leak. shut off valve or activated Charcoal Canister - PO 456.

Any help is appreciated.
I can change the part myself if I knew where the hell they are lol

DanielFD

the purge valve is an extremely easy repair and pretty cheap just Google that and see how easy it is. As the activated charcoal canister.. i have no idea, i do know its related to the fuel tank and they are known to fail.

pskdude

after replacing the purge valve with no fix.... i had the check engine turn on today going home from work. Definitely felt a misfire. Hopefully it was related to the rough idle. Ill post today the results.