Ruiner

Over the past few months, I have small issues with my fuel trims (typically only the Short Term Fuel Trims are affected). I suspected the MAF to be the problem, so I cleaned it and things "appeared" to return back to normal for a few months (less hesitation and no CELs). I had the previously mentioned "bucking" and hesitation under low speed, low rpm throttle. Recently, the CEL has come on a few times; perhaps once a week or so.

Looking at my fuel trims today after my drive to work (36' F) while the car was cooling down at idle:
- my LTFTs were both: +3% (left and right bank)
- my STFTs were both -3 to 0% as they cycled (left and right bank)

Now, this doesn't look too bad and is easily w/in the range of values. As I am sitting there, I get my famous CEL:P0175 System Too Rich (Bank 2). Sometimes I get P0172 (System Too Rich Bank 1), but not this time as I typically clear the code before it has a chance to throw the other bank as well.

So, I clear the CEL and look at my fuel trims:
- upon resetting a CEL, your LTFTs go back to: 0 (left and right banks)
- I look at my STFTs, at idle, with the LTFTs at 0 as they zero-out when you clear a CEL like that: -22 to -18% (cycling - both left and right banks)

It appears as if my STFTs are what trip the CEL light as they are approaching -25%. They were just at -3 to 0% before I got the CEL, when the LTFTs were +3% each. I never saw them get below -3% or so when my CEL came on as I was watching it when it happened, yet the light still came on. Any explanation?

I am still thinking that this is my MAF as your system will typically run positive corrections under throttle/load and negative corrections under idle if the MAF is bad (if I am wrong, please someone correct me).

Any ideas?

Oak

what kind of mods?

tkerrmd

Boy I wish I knew what you were talking about I feel so dumb!!!

Ruiner

Turbo Exhaust v8.0 + Baileys Diverter Valves; stock ECU

'01 w/ 34k on the clock

Dock

I'd have to say it's the MAF.

Ruiner

I figured the much, Dock, but I guess I wanted to know for sure. I swapped in Frank's MAF and didn't notice that much of a difference. Then again, I didn't get a CEL so that I could reset my LTFTs while it was in, so the test wasn't as good as it could be I guess.

Dock

If I were you, I'd drop by J. Ellis and bend Craig's ear on this issue before springing for a new MAF.

ebaker

It's strange that the STFT would suddenly go from 0 to -20 while you're just sitting and idling. Maybe some oil or lint got on the MAF or maybe the MAF is failing with an intermittent electronic fault. If your datalogger is working correctly the ECU should move the short trim gradually towards zero and the long trim towards -20 if you drive around slowly.

Ruiner

It "only" went to -20ish when the LTFTs were set back to 0 after I cleared the CEL. However, this is not the first time that I have seen the STFTs dip into the -20s (one of 10 times give or take). However, it would take a -25% or so in order to throw a CEL (which is what I got).

The problem is that I never get my LTFTs to hit the extreme +25 or -25. I typically throw a CEL before that happens (I have seen them as high as +7 or 8). When I clear the CEL, the LTFTs zero-out. I do know that a symptom of a bad MAF is LTFTs (STFTs as well) in the positive range under throttle and STFTs in the negative range at idle.

Ruiner

As usual, you are probably right, Dock. Craig S., correct?

Dock

Yep.

Woodster

Take it to your local dealer and have them diagnose your problem,
time is money also!

good luck!
Marty K.

Ruiner

I'm stubborn to an extent. I enjoy being able to solve problems on my own. I ordered a Boxster 986 MAF from AutoHausAZ for $210. If it comes down to it, I will take it in to the dealer, but I can do most of my own work and will continue to do so until (if) the problems get beyond my control.

GreggT

Ruiner........heck of a deal on that MAF.
But hey, what are you going to do for a hobby after you get this solved
........seriously, please come back and let us know if this solves the problem.

Ruiner

Oh, I'll figure out something else to do. I have a new set of brake pads (Mintex) and want to change my oil, so that will keep me somewhat busy. I still have a stock ECU, so we will see how well the Boxster MAF does with a stock, 2001 ECU (if I need to flash the DME or not). This might be an easily, more stable solution to those with MAF issues. Keep your fingers crossed and I'll report back as soon as it arrives (it shipped today).