Replaced Air Filter and now she idles badly and stalls
 

Hi!

Hoping for some help as always. I replaced the air filter in my Boxster with a new K&N filter. I read afterwards that some people have some problems with it, hmm.

Anyhow when I pulled the old air filter out there was a lot of debris that went everywhere - dust, stones, twigs. I used damp kitchen towel to remove it all from the air filter compartment and made sure there was nothing left.

I gently lubed up the filter tray ribs like the instructions say and placed the filter in.

But now, she idles between 600-1000, going up and down. And if I let the revs fall too fast like at a traffic light, she stalls.

Has anyone had this problem? Maybe I didn't put enough lube and there's an air seal problem? Wanted to research before I try to fix.

Thanks so much as always :-)

John

P.S. DAMN she is faster now she doesn't have an old filter in her. After 4500 revs it is a pleasure.

Hmm done some analysis and I think this must be a vacuum problem or a MAF problem. It reminds me of a Golf I had, that had a small vacuum problem - funny idle and stalls if the revs fall too fast.

In case the K&N doesn't fit right I'm going to put the original filter back and see if it fixes it. That should remove the possibility of the vacuum problem though I don't have a smoke machine.

Otherwise I guess I have to go and get some MAF cleaning fluid and clean that - possibly I contaminated the MAF when I removed the old filter? Fingers crossed...

John

Did you oil the new filter? I believe the new filter already comes pre oiled, and oiling it would over saturate it.
Also, did you disconnect the battery for 15 minutes? The car's computer has "memory" and may benefit from just a reset. Just a thought.

Thanks for the reply Kenny.

I read it came pre-oiled so I didn't do anything before I put it in. It didn't look heavily oiled so I didn't soak it in kitchen towel or anything.

I put the old filter back (it goes in much more easily) and the same problem is there though it is not so prominent. Thanks for the tip on the reset, I'll try this next.

I also noticed that the seal on the air filter tray looks a bit worn. Could this be causing a vacuum problem?

John

If your car ran fine before the K&N and only acted up after the new air filter was installed, most likely its from the oil particles mucking up the MAF sensor. Try using a MAF cleaner sold at auto stores or get a new MAF sensor. It happens more than you think and this is not so much mentioned in the K&N ad.

I use an oem air filter, works the best, and I also just changed my MAF sensor from a CEL P1128 code saying the left bank running lean. After installing a new MAF sensor and resetting the CEL with a OBDII scanner, it solved my problem. No lights for 2 months and the car runs like new.

Best

OK so left the battery unplugged for a while, same problem. Took it to my mechanic that usually services the car and we looked at it together - he agrees that I didn't screw anything up :-)

Guess next step is to clean the MAF sensor. Doesn't look too hard, the throttle body looks tougher.

Now the car is starting to hesitate, need to change down and rev and it is OK again. Does that symptom mean anything?

John

By the way I'm not getting any CEL. I may hook up my OBD-II to her just to check if there are any messages.

Air filter clogging MAF is a known problem. Use a search to see.

Get rid of that air filter before cleaning your MAF and writing it off to an inexpensive 986 lesson... (there are much more expensive lessons).


/

An update... no way to get a stock air filter at the weekend around here, so I cleaned the MAF and put the K&N back. She ran great for a while (better than ever) and then got bad again.

So either it is the K&N or it is the MAF which is bad. A stock filter costs $20 and a MAF costs $240, wonder which one I am going to try first :-)

I really didn't want to believe this stuff about oil coming out the K&N and into the MAF, and K&N heavily refute this and have done a lot of tests which claim that the oil residue is BS. But, my testing is clearly pointing to the K&N filter not working in some way.

K&N Mass Air Flow Sensor Test Results

Thanks as always. Update tomorrow when I have secured a stock filter, re-cleaned the MAF and test driven her.

John

Well, the Porsche folks here say one thing, and K&N another......listen to the Porsche folks.

Just stick with paper filter... you can change it twice as often if you're concerned about it getting dirty and degrades performance...

Go ahead and ask me how I know this.

Agreed!!! Installed a K&N and went back to the PAPER!!!! Throw it away

So I'm still stuck :-(

Replaced the K&N with a paper filter, cleaned the MAF sensor, she seems OK for 10 minutes then when she's warm, the hunting at idle and hesitation starts again.

Any ideas what to do next? So frustrating!

John

Did you change the filter and unplug the battery again to reset?

Try cleaning the idle control valve. I had a stalling problem this summer. Pretty much the same symptoms. Cleaned the throttle body and the control valve, problem solved. You can take the the idle control off without removing the throttle body.

Yep - unplug the battery for 15 minutes every time, just in case.

I have an '01 2.7 which I believe means it is E-Gas so there is no ICV. Instead, the throttle body modulates the butterflies to retain a good idle.

I guess therefore it is logical that the butterflies may have some gunk in them, and that would explain a rough idle and hesitation. Guess it is time to man up and clean the throttle body - was avoiding this, to be honest, as it looks fiddly!

John

Removing the throttle body is a PIA. My idle problems cleared up after removing the the intake duct to the throttle body and spraying cleaner all around in there without removing it. Snapping the duct back on took a little elbow grease too but warming it up with a heat gun helps.

At this point I would get a new MAF sensor, yours is no longer good even after you cleaned it.
Put back an oem filter, and use an obd2 scanner to reset it, should be fine after that.
If the maf is bad, it doesnt matter what filter u use it will affect the fuel/air mix and cause the car to run rough.
I don't believe its your your throttle body controller as I just went thru this myself and a new MAF fixed it.
The MAF sensor comes in 2 types, with and without E-Gas/E-Acceleration, need to find out which your car uses.

Air Mass Sensors are also known as the: Air Flow Meter, Air Flow Sensor, Air Mass Meter, MAF, Mass Air Sensor, and Mass Flow Meter.
The Air Mass Sensor measures the air mass that flows through the air filter to the engine.
This information is then sent to the control unit in order to specify the fuel injection rate.
Common symptoms for an Air Mass Sensor that needs replacing include:

- Erratic Engine Operation
- Reduced Performance
- Engine Stalling or Cutout
- Increased Fuel Consumption

* Please remember to reset the ECU after replacing the MAF or the car may continue working as if the old one was still installed. * (by unplugging the battery or reset tool).

best

My car came with a K&N, I have done the normal clean and re-oil a couple times with no detrimental effects. I started getting the hunting idle.
I did a complete Throttle body, tubes, MAF (Use MAF cleaner) and now my idle is rock steady
I had switched to a K&N on my mustang and was concerned about the MAF getting fouled but it never effected it

I think you need to see what residue maybe lurking in your throttle body and using some MAF cleaner.

I've used K&N air filters on my Z3 and Z4 without any issues. Porsches and Ferraris are not recommended as the oil particles from the filters will foul up the sensitive sensors. You might get lucky based on how much oil your filter has on it, but its a guessing game and luck at this point. No thanks, not worth the gamble.