2006 XC70 MAF code with issues

[EngineeringBloke]

While the Volvo DICE diagnostic unit is great and provides information you can't get from a cheap alternative, I drive with an ELM327 Bluetooth unit (about $12 from Amazon) and use the Torque app (Torque pro is $5) on my Android phone to monitor via the ODB2 engine diagnostic port under the dash of my '06 S60. Torque allows you to reset the check engine light and clear the current stored error codes.

[jimpierce7]

While the Volvo DICE diagnostic unit is great and provides information you can't get from a cheap alternative, I drive with an ELM327 Bluetooth unit (about $12 from Amazon) and use the Torque app (Torque pro is $5) on my Android phone to monitor via the ODB2 engine diagnostic port under the dash of my '06 S60. Torque allows you to reset the check engine light and clear the current stored error codes.

NICE!!! I'll have to look into this!

[abscate]

The mechanic should have spent the hour monitoring fuel trims and fuel pressure to track down the problem. If they are just throwing parts at it, you add labor costs to the cost of good parts replacement.

My 1999 had a hose split that came and went, causing rough cold idle, that showed nicely on fuel trims

Using aftermarket parts like a MAF will make you chase your tail even faster. These cars like OEM on critical stuff

[jimpierce7]

I'm learning this. The mechanic that did the diagnostic did a smoke test and inspection on the vacuum lines. All came back good. Until I get a good MAF on it I'm not doing anything else. With the new O2 sensor it is smoother once warmed up. But the most recent MAF is worse than the original was at cold start. If the newest one is still no good I'll have to bite the bullet so to speak and go to Volvo.

[jimpierce7]

All the Norse Gods willing, I may have actually found a good MAF. I'll know for sure in the morning. O'Reilly was going to take 5 to 7 days to order another, as after two so far I decided to call Autozone to see if they had one. I couldn't go 5 to 7 days running as it was. Each new MAF made it run worse than the one before.
She is running substantially better now.
Sheesh.
This holds true my next adventure will be a timing belt.

[mrbrian200]

I've been through this. Sounds like your mechanic is just following the recommended actions displayed on his diagnostic tool. I don't think that's going to do it in this case. He needs to dive deeper - which involves watching and understanding live data, and probably a smoke test. Quite a few mechanics will be in over their heads on modern vehicles when you bring them something with a little funky going on.

MAF code and rough running at various times but more often just after startup when hot. Gaskets tend to leak more when cold, so that's probably down on the list.

An intermittent bad reading from the coolant temp sensor can cause this. A air charge/temp sensor might do it too. It's not on the manifold on these cars. It's a combination air pressure and temp sensor. Technically not a MAP as it's before the throttle plate, not after.

Because I've had problems with this on my '06, and it could cause your symptoms, I'll mention:
Have your mech check the throttle body. He'll need to record live data during one of those rough starts. Also observe how the throttle plate position acts while driving. Throttle plate position (as reported by the TPS) should be no higher than around 7% open during hot idle in park. While driving you slowly press and release the accelerator pedal and look for spots where the throttle plate appears to be sticking.
In my experience a sweep test with the engine off looks like there's nothing wrong with it. You have to perform functional tests while the car is starting/idling/rolling down the road.

The ECU command output to the throttle body isn't necessarily linear to torque request (accelerator pedal), but most of the funnier stuff the ECU does in this regard happens with quick changes on the accelerator pedal and during hard acceleration to moderate hard gear shifts. On a longer 10-15 second sweep between foot off and about half way down on the pedal and vice versa you should see a smooth predictable correlation between the two.

If any of the above turns up nothing you probably have a air leak and just aren't finding it. Could be almost anywhere including PCV, power brake system, vacuum check valves, or even the evap system, hoses, purge solenoids etc. Hence a smoke test might actually be the faster way to find and remedy.

[jimpierce7]

Thank you very much for the input!! I seem to have struck pay dirt as with this new MAF combined with the upstream O2 sensor. She is running good again. With all this it is time for a new timing belt as well. I'm going to keep in mind the above just to be sure as there is a slight bit of roughness in the idle. Very slight but it is there. Until it is all the way warmed up.
I'll be looking into the throttle body as it has been mentioned a couple times.
A smoke test has been done and there were no leaks.

[EngineeringBloke]

Interesting. During my commute this afternoon (13 mpg for the 5 mile trip mostly on highway with moderate traffic - 3 lights and it is quite possible that I was not hypermiling at all ), I see that the throttle position manifold only closes to 12.16% (ELM327/Torque) during downhill braking when I would have my foot off the accelerator at the highway exit. Later, going down a steep hill, I see the minimum for the whole trip - 11.76% - it never ever goes to 7%. I do have my aftermarket amp, A/C and seat heater on. I will test with those all off to see if I find a difference.

I wonder if the throttle is truly not closing due to a physical blockage or issue within the ETA, or if it is commanded to stay partially open -7% LTFT.

mrbrian200, I remember you taking your ETA apart and finding heavily worn plastic gearing - we have the same model/year. However, I an not aware of any notchiness in my cars response to the pedal.

My Torque app Trip View map shows readings at about a second interval when you zoom in to the route.

Still not sure what the underlying cause is. I am installing new Volvo OEM plugs and a new MAP sensor when it gets a little warmer (perhaps tomorrow). I also plan to try spraying some brake cleaner around the cold running engine to see if I can pick up a vacuum leak.

(Sorry for jumping on your thread, Jim)

[mrbrian200]

I'm not sure how it's supposed to act when you take your foot completely off the pedal at higher speeds. I know where it should sit at warm idle in park which is a controlled condition that shouldn't vary too much from one vehicle to the next with the same/similar engine configuration. Which in this case would turbo 5's with the Bosch ETA. I'd check but am with relatives in the city with no close access to a highway for the next couple weeks. I always get confused with fuel trim numbers. Negative means it's adding gas to compensate for a lean condition or the other way around? If you're using VIDA, put it in graph mode displaying the throttle position, STFT, and torque request/accelerator pedal position. If it's going lean during those higher speed deceleration maneuvers that would probably be good enough evidence to me to consider that the ETA may have an issue.

[EngineeringBloke]

I think I need to start a thread of my own, but I did just run the engine in the driveway. It was cool, but the revs came down to 665. I will redo the test on a warm engine but the throttle never went below 12% with no amp, heated seat or A/C.

And my LTFT is 7% positive (not negative) which I understand to mean positive addition of fuel to compensate for unexpected additional air - perhaps a leak in the intake piping after the MAF (or under measured air at the MAF).

Looks like I should check the throttle plate is clean and free to close. And perform an intake leak test.