Low MAF reading, high LTFT but no vacuum leak - what to check next?
 

When my engine (just past the 50,000 mile mark on my 2009) is fully warmed up and idling (~800 rpm; everything off radio/fans/AC/etc), my MAF is reading 4.1-4.4 grams/second, and my LTFT are +12. Pretty standard symptoms of a vacuum leak (there is also an audible high pitched "chirp" that sounds like a vacuum leak as well).

So far I've cleaned the MAF (wasn't visibly dirty to begin with but what the hell) and re-set the fuel trims - no change. Cleaning the throttle body, which was slightly oily, also had no affect (curiously, calculated engine load at idle went from 30-33% to 29-31%, and the MAF readings started to hit 4.1 more often). Tried to track down any vacuum leaks myself, couldn't find any, so I took it to the dealer to get it smoke tested. The smoke test didn't turn up any leaks. I spoke with the tech at length, and he insisted that it was the P0420 being thrown by my midpipe that was adjusting the fuel trim. When I postulated how this could possibly cause the MAF to read lower than normal he provided an incoherent response in which he referred to the car's "4 cylinder" engine and rich smelling exhaust. He also said that the MAF itself shows no signs that it is faulty or has any frayed wiring.

So my question is where do I go from here? The only other "clue" is that on 3 occasions this summer on hot days, when the car was repeated shut down/restarted in rapid succession with the engine hot (such as getting gas, then going 1 mile to the pharmacy, then going 2 miles back home), I would get a P0111 as pending. On all occasions the P0111 would clear itself within a day or two and never went beyond "pending" status. Monitoring the intake temperatures revealed no abnormally high/low readings under normal driving conditions (10-15 degrees F over ambient).

Thoughts? All I can think of is to re-check the grounding for the MAF. :banghead:

UPDATE: Just made this connection - the high pitched "chirping" that I previously mentioned sounded like a vacuum leak goes away when I push the clutch in. It then returns almost exactly 3 second after the clutch pedal is released.

Check the SSV shaft for wear .............grab it with your fingers and see if it has much freeplay

Check the tube the MAF is in for cracks, and every hose that attaches to it. Smoke is usually applied downstream of the butterfly, but air getting in before the butterfly, after the MAF, will cause issues as well.

Do you have a catch can? Is it vented? That will do the same thing.

As far as I can tell there isn't any discernible play in the SSV. However, being buried behind a myriad of hoses and various parts, it's hard to get my hand in there to really tell for sure. Perhaps if I remove the air pump I can get a hand in there a bit better?

I've gone over the MAF and every hose running off the intake with a fine tooth comb and haven't been able to turn up anything. I will proceed to triple check these components.

The car does not have a catch can installed.

So, the car keeps trimming itself to put in more fuel. One reason is extra air is getting in, the other is that not enough fuel is getting in. Check fuel pump..

Also, check midpipe for leaks. I have no idea why, but when I had a crack welded in mine, before the second o2 sensor, my LTFT dropped about 2% almost instantly. I thought that sensor was only to check on the CAT (um, missing) but it may collude with the front one. If the crack was letting air in between pulses, then the sensor would read excess o2, and think it needed to add fuel. At least that is what I made up to explain the effect.

Would a failed ignition coil possibly cause this?

I haven't had enough time to pull the air pump out to get at the SSV yet, but I have gone over all of the hoses running off the intake again and came up empty.


While I can certainly understand that any leaks upstream of the second O2 sensor could plausibly explain some of the fuel trims - the thing that I can't seem to rectify is the low MAF readings. :scratchhe It's clean, but it seems prudent that I verify (a) that the numbers I'm seeing via OBDII access are the same as what the MAF is actually reading, and (b) that the MAF itself isn't faulty.

The fact that the "chirp" goes away when the clutch is engaged is another area that I haven't had time to fully explore, but it seems like a red herring since it has no correlation with the MAF readings.

Thoughts?

Thanks for all of the input. I will continue to pursue all suggested avenues - it's just a matter of having the time to do it.

Chirp could be release bearing. Does it go away as soon as you touch the clutch pedal? If so, look up "free play" for the clutch pedal. If the release bearing is touching the pressure plate, and making noises, you might be in line for a release bearing failure. you can likely adjust things so it does not touch, but I would get that looked into. It may be more important than the fuel trims. Mine ended up in 20 something pieces and I towed it home.

Definitely have too much free play in the clutch, and as predicted the chirp stops as soon as the clutch is moved. My attempt to adjust the play this evening was foiled by the locking nut - which I was not able to get off (combination of requiring more force than I was comfortable applying and the bad angle making it hard to apply any force). Hopefully I'll have better luck (and more sunlight) tomorrow.

UPDATE: Adjusted clutch free play to within spec (was just 3 mm's outside spec originally), and while the chirping has decreased in volume, it is still present. I will continue to play with the clutch free play to see if any additional adjustment can alleviate this. In the event that the release bearing continues to make noise and needs to be looked at, would there be any substantial benefits in having a new clutch put in at the same time? (car doesn't need a new clutch, but if the release bearing requires removing the transmission to replace it seems like I could stand to save money on labor if it's all done at once)

Ever found the maf problem? I have the same issue

Yeah, that sounds like the throw out bearing.

I think it's always best economics to check pressure plate, and put in clutch plate and maybe pilot bearing at the same time.

Keeping plate with the clutch freeplay to stop throw out bearing from running is key to it's life.