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Discussion Starter #221 (Edited)
Elevated HC with no CO often means the engine has a slight lean misfire, like from a vacuum leak. But if the car was running well in closed loop mode when the HC was measured, with the O2 sensors switching normally (at idle, the switching rate is slow, every 2-3 seconds), and the lambda integrators and adaptations in the normal range, then this rules out the usual problems like vacuum leaks IMO, and the two likely problems are a degraded cat (or cats), or an O2 sensor drifting and reporting good AFR when in fact it's not.
The pre cat sensor worked fine when in idle (at the measurement ), and the post cat sensor gave 0.72~0.74 V (Is this high level because of high HC?). The lambda integrator was around 1.05, I think.

How old are the O2 sensors? Any B2/B3 cats codes?
No codes at all. The all four O2 sensors are only four months old. They are all Bosch-made.

Yes, the ignition timing on all cylinders is locked at 15 deg at idle, but it should change significantly while driving. Do you not see this?
I did not know the ignition timing on all cylinders is locked at 15 deg at idle. Thanks. I have not measured them in driving around.

Re exhaust cam timing, it depends what you mean by randomly. The exhaust cam is the one that changes a lot during normal driving whereas it takes quite aggressive driving to change the intake cam timing.

Why are they dubious about the between-cam tensioners? They are pretty reliable.
The pic below is from the post #172. The exhaust camshaft angle do not change in consistent manner (around 4 deg which the DME commands). They think it could be caused by slacks of the chains. Of course they are not 100% certain. The solenoids could be the cause. They think mechanical part should be aligned before we say something about sensors and control.

Re gas mileage, if the car is working normally in closed mode, maintaining the AFR at 14.7:1, then the only two factors that affect it are the ones that involve working in open loop mode, i.e. the warm-up enrichment time and the time spent driving aggressively.
What about long idle in congested traffic? As usual I had a lot of idling time (a lot of HC?) during the round trip.

In your case, the second factor doesn't apply, and since your car now appears to be running well in closed loop, the gas mileage is affected only by the warm-up enrichment time. This is very dependent on ambient temperature so naturally as the weather cools down, gas consumption increases. This may be what you are seeing. 15 mpg doesn't seem to bad to me, especially if it's US gallons.

And of course, the t/s has to work well.
I do not think the warm-up enrichment time matters because it take only a small part in the total driving time of nearly 3 hours. And the ambient temperature was around 10~12 C (50~54 F). I have to correct the average speed. It was more like 50/3 = 16 mph (not 30 mph).
1 Gal = 3.78541 L (by my hp calculator). I believe this is the US gal.
 

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Discussion Starter #222 (Edited)
More on the MAF

Now the security torx arrived and I remove the sensor part from the duct.
The opening to the sensor is very small and it is hard to see the film sensor surface. I could barely see dirt and a few lints. Cannot say it is very clean. The lints could be a part of the house dust. My living room cannot be said to be a dedicated clean room, and my cat came and saw.

With that said a spraying the cleaner with the duct on may be of no use. Spraying through the front lattice at the sensor opening is very difficult.
Removing the sensor assembly from the duct may be necessary. Also a brush or a cotton swab is needed too, though it might break the film sensor.
According to the mechanic at the shop he was told at a Bosch training the sensor cannot be cleaned.

The smallness of the opening to the sensor makes me think it is due both to increase sensor sensitivity and to limit airflow within the sensitivity.
Although the airflow passage forms a U-shape with the exit facing down, there is another passage above it. It is, contrary to the sensor passage, straight.
It may be for cooling the circuitry.

Btw the torx is very good considering its price of less than $3 and free shipping ( I found it at ebay). Unfortunately the six-point is on the longer end it is a bit hard to torque it.

In the pic below the magnifying glass I used is also shown(sorry for the poor quality).
 

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The pre cat sensor worked fine when in idle (at the measurement ), and the post cat sensor gave 0.72~0.74 V (Is this high level because of high HC?). The lambda integrator was around 1.05, I think.
The normal post-cat reading of steady 0.75 V means there is very little O2 in the exhaust post-cat. I guess that's because it's doing it's job well, both storing O2 and combining it with HC and CO.

LI's around 1.05 indicates lean running. LI's should be bouncing either side of 1.0.

The pic below is from the post #172. The exhaust camshaft angle do not change in consistent manner (around 4 deg which the DME commands). They think it could be caused by slacks of the chains. Of course they are not 100% certain. The solenoids could be the cause. They think mechanical part should be aligned before we say something about sensors and control.
Doesn't look too significant to me. Try looking at the exhaust cam values after a cold start. The timing goes to about 35 deg. How much do they bounce around then?

What about long idle in congested traffic? As usual I had a lot of idling time (a lot of HC?) during the round trip.
Ah, yes, I forgot about idling. Sometimes while sitting at idle, over 20 minutes I can see my fuel consumption on the NAV screen increase by 1 litre/100 km. It's very dependent on when you last reset the reading.

I don't know how the DME calculates the reading if you reset it and then just idle, because technically you are getting 0 mpg, or infinity l/100 km!
 

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Discussion Starter #224
Doesn't look too significant to me. Try looking at the exhaust cam values after a cold start. The timing goes to about 35 deg. How much do they bounce around then?
Sorry for the late reply.
I tried a cold start (the OBC temp was 7C) and monitored the exhaust camshaft angles with C110.
Basically they jumped to 37~38 deg, bounced maybe 1~2 deg range and continuously went down to around 4 deg at 700 rpm (Just one yellow LED of the tachometer was put off at that moment). Naturally it was not easy to see the neutral points around which they bounced at the very start, since they were not stable there.
So the VANOS for the exhaust seems to be OK.
 
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