I've had ongoing issues with my original MAF sensor for a few years now. I had it into the dealer for diagnosis of pinging and they told me the MAF was giving some bad readings. It would always run smoother/shift better after I cleaned the MAF with some spray. Long story short, I finally purchased a new OEM MAF.

After I put the new MAF in the car drove beautifully. No pinging, completely smooth shifting, throttle response like I hadn't felt in years. About 5 days in, it started to have an odd issuing while warming up. When driving around 35 mph uphill, it would upshift, then lug and surge 1-2 times before downshifting and running normally. This only happened at one particular temperature between Cold and Normal. No problems when cold, no problems once hot.

I few days of this go by and I figure it had learned some odd fuel trim or shift pattern. So I pulled the battery for an hour to reset. Put it back on, and sure enough that problem was gone. Unfortunately, here we are 5 days later and it came back with a vengeance. This time it's right about the time I reached normal op temp. I slowed to 40 mph for traffic, then when pressing the gas to accelerate it completely fell on its face. Lugged and surged 4-5 times until it finally accelerated. After that it ran normally again.

I'm at a bit of a loss. I'm not sure exactly what this feels like--not quite a misfire (doesn't feel like a single cylinder miss), but not quite a transmission shifting issue (trying to lock the torque converter when it shouldn't?).

Fuel trims are looking fine, and about the same as they did with the old MAF (LT -5% bank 1, -3% bank 2 at idle, close to 0% both off idle).

Any thoughts or suggestions?

Thanks,
-Michael

 

What's the status of your o2 sensors? If original, they could be failing without throwing codes.

 

They are the originals. I've heard differing opinions on whether O2s should be replaced as wear items or not. Car has 113k miles now.

I don't mind replacing them if they are bad, but I'm not sure I see how they are playing a role in this issue. They had no problems with the old MAF and only cause issues with the new MAF after a week of learning parameters, and then only for a moment or two during warmup... do you think the downstream are not warming up properly and then when the do they suddenly cause a change in mixture?

Would you do all 4 or just upstream only, downstream only?

 

They should definitely be replaced as a wear item between 100k-150k, sooner the better.

Unfortunately, the relationship between the MAF and o2 sensors and specifically what they all do together and how and when is beyond my knowledge. But what I do know is that I was having similar driveability issues that were temporarily solved with a new MAF, but turned out to be the o2 sensors in the end. Once I replaced all four, the car became brand new again.

I admit I was just throwing parts at the issue without really understanding it, but it worked for me. I'm not saying that your particular problem is indeed the o2s but its definitely something to keep in mind.

 

Has the fuel filter been replaced?

 

Update to this issue: I put back the old MAF and still had the stumble/stutter. So I reset the battery and the problem remains. So this issue appers to be unrelated to the new MAF, which is good news at least. However now I can't figure what would cause it to occur as such different times. Today it happened a block from home on a cold start, stumbled a few times and that was it. Yesterday it was fine until I tried to accelerate onto the highway. That time the stumble was at 3k rpm, but I was 5 miles from home and the engine was fully warmed.

Doesn't feel like a misfire. It feels the same as when you let an engine hit the rev limiter. Fuel filter was changed, but don't see that as the issue. It's too intermittent.
​​

 

Could be any of a few things but maybe a perished hose that flexes so a hole appears briefly.

If it's that then watching (realistically: recording) fuel trims (short ones) should show it up.

 

Hello, did you ever find out what caused your MAF faults. I have the exact same problem with my 05 XJR, PO103, I replaced the MAF with a new one, not OEM, but a new Denso unit. I did find a crack in the intake tube leading into air box. Still my PO103 fault persist. I disconnected the battery, but not both leads. I do not have the code to reset radio.

John

 

Check the wiring & connectors (through to the PCM if needs be) if the MAF is good.

 

jpmc86 wrote
I do not have the code to reset radio.

Never had to reset mine, had it disconnected for at least a week at a time, more than once.

 

Ever geta a result on this? sounds like what mine is doing

 

I eventually replaced the fuel rail pressure sensor and that cleared up all stumbling/running issues.

 

Any chance the PCV valve is gunked up? I had a similar issue a couple years ago and the MAF and PCV were the culprits. Just a thought as I am definitely not a diagnostic mechanic.