fpena944

I have an issue that really wipes out the amount of fun I can have with my car.

When accelerating and hitting the upper RPM range, I frequently get a misfire on cylinders #4 or #5.

I thought it was the coils so I replaced those last week but the problem still exists.

So I did some reading and found that someone once had some unexplainable CELs come up and found that it was their MAF. I tried to test this theory by disconnecting the MAF and trying to replicate the CEL. Without the MAF I didn't get the misfire anymore.

Now my question before I spend another $300 on a MAF, could this potentially be the issue? I just find it strange that if it is I would only get errors on one side of the engine. This past weekend I did remove the entire air box assembly and MAF to clean it all out. It looked clean (even the throttle body) but I still sprayed it down - didn't make a difference.

Any ideas anyone?

Topaz330ci

Did you clean the TB with a cloth and literally no dirt was on it?

wyovino

Just curious, did you clean the MAF sensor as shown here?

http://www.6speedonline.com/forums/9...sor-clean.html

fpena944

Yes and I also used "throttle body cleaning spray" that I found right next to the MAF spray at Advance Auto Parts. So in the case of the throttle body I used both the spray and a cloth. It had a slight film of grime on it but for the most part was pretty clean.

I did. I took the whole assembly apart, checked the rubber hoses on the airbox to make sure I didn't have any leaks and sprayed the crap out of the MAF. The MAF was also clean but I figured just in case I would spray it liberally.

The car ran very rough for the first 30 seconds or so after I put everything back together again but then it began to idle normally and I took it out on a test drive. On the drive all is well until I floor it and hit over 5000 RPM. At that point I get the misfire again on cylinder #4. So frustrating!

Barn996

Are you getting any CELs?

Barn996

I paid about $156. for a new MAF a year ago. I had previously spray cleaned my MAF but it still produced CELs after a couple of weeks.

chsu74

egas MAFs are more expensive. $233 at autohauz vs $168. I replace mine every 2-3 years because of CAI oiling it up and its just not the same after.

http://www.autohausaz.com/search/pro...0Mass%20Sensor

Barn996

That's where I bought mine last year Chao. Non egas.

fpena944

If I rev the car up through redline I'll get a P0304 or P0305 CEL.

Sometimes it'll clear up if I ease up on the gas quickly but other times it stays on and I have to clear it manually.

Spark plug wires are in good shape and the coils have been swapped out so that's why I was wondering if maybe the MAF could be the root cause here.

Macster

The answer is yes the MAF could *potentially* be the cause of the misfires.

On another board I encountered a Boxster owner who reported misfires on just one bank. I forget the bank. He tried all the usual things: coils, plugs, 'bad gas', and I forget what else.

He either disconnected the MAF or simply replaced the MAF and the misfires went away, AFAIK, never to return.

I would not advise you to replace the MAF without more confidence that it was the source of the misfires.

You disconnected the MAF. Did you clear the DTCs to among other things reset the fuel trims to their defaults?

Then drive the car as you did before. You need to give the DME time to detect -- if there are any to detect -- misfires so just a quick spin around the block is not going to do it.

If you give the engine every chance to misfire and it does not, then clear the DTCs again and reconnect the MAF. Drive the car again. See if the misfires return.

If they do I have to say that this is not 100% proof the MAF is the cause. It could be with the MAF disconnected the DME varies the fuel or ignition timing or varies the valve timing (and if VarioCam Plus present the valve lift) of the engine in such a manner that the misfires are avoided.

If at any time the engine gets sicker, makes any noises, behaves in way out of the ordinary, shut off the engine pronto and get the car to an expert for evaluation.

Sincerely,

Macster.

ferryman

Maf sensor usually runs rough and gives a lack of power in my experience, i'd be looking at the solenoid for the cams first in case there is one off,or even swap side to side to see if the fault moves with it !

fpena944

Macster - Thanks for the response and help with troubleshooting.

When I disconnected the MAF I ended up getting some PSM and ABS errors but no CEL codes. I didn't clear anything and figured these errors would continue as long as the MAF wasn't functional. I didn't like driving the car for very long without it connected so honestly my test was maybe 5 minutes at the most. I ran it through the same scenario and no codes appeared.

But as you mentioned it is likely that I was now under a completely different fuel mapping scenario so perhaps the test wasn't really valid.

Once I reconnected everything the PSM and ABS errors were gone and all instruments were back to normal. But when I floored it I ended up with the P0304 error.

No other symptoms appear on the car and it runs great each day except when I go wide-open throttle and hit the upper RPM ranges.

Based on what Ferryman states below about the cam solenoids, would that be a possibility? I try to do as much as I can by myself on this car but I might have to throw in the towel soon and take it to the professionals.

The car runs fine so I'm not experiencing the rough running symptom. I'll do a search on that problem and see what else I can learn!

gixxe638

i have same thing what did you find out

Macster

In the original thread, I never responded again to the OP. Why I don't know.

Maybe I can make it up some….. You say you have the same thing going on with your car? What model/year? Need more info. What have you done to the car? A bit of history on the car would be nice.

gixxe638

my car is a 2002 996 c2 with 33000 miles on it i use the car on the track more then the street. i changed the coils, plugs and the MAF and no change. above 5200 rpm it starts to brake up from idle to 5000 rpm it runs good. i get a code of misfire 4,5, and 6 most of the time but when i unplug the maf there is no change in the car but the code is not a misfire anymore but a maf sensor