You are on thinking correctly- In fact, I would be a little suspicious of the mechanic guy from now on. So, what is the LTFT and STFT doing? are the O2s cycling high to low? are you SURE you have no vacuum leak? have you carefully examined the air plenum that runs from the MAF to the throttle body? Is the full load breather tube cracked? Sometimes tit is hard to see the crack on the breather tube. If all of that is OK, I would be looking for problems at the MAF.

 

Do you knwo how to check the MAF? Is there a certain procedure to determine if it is faulty?

 

See if this troubleshooting link might help. http://www.gusglikas.com/AutoRepairTroubleShooting.htm I found my leaks at times by going back a second time, in fact the one on my S-Type I was told where to look before I found it. It could be the MAFS and aside from using a high-end OBD reader or have another to swap it out I am not sure how to check it. If you had pin readings to compare you may be able to identify the problem.

 

Well, I was not able to map the O2 data on my scanner, but I was able to get freeze frame data. Not sure if these are normal:

Control Module
$11 ISO 9141-2
Live Data
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 866
MAF(g/s) 5.98
O2S B1S12--B2S12--
O2B1S2(V) 0.135
O2B2S2(V) 0.120
O2S21(mA) -0.586
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 750
MAF(g/s) 5.22
O2S B1S12--B2S12--
O2B1S2(V) 0.090
O2B2S2(V) 0.070
O2S21(mA) -0.637
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1726
MAF(g/s) 15.35
O2S B1S12--B2S12--
O2B1S2(V) 0.735
O2B2S2(V) 0.335
O2S21(mA) -4.004
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1948
MAF(g/s) 24.73
O2S B1S12--B2S12--
O2B1S2(V) 0.150
O2B2S2(V) 0.115
O2S21(mA) 0.977
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 3200
MAF(g/s) 25.12
O2S B1S12--B2S12--
O2B1S2(V) 0.395
O2B2S2(V) 0.275
O2S21(mA) -0.293
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 3164
MAF(g/s) 24.44
O2S B1S12--B2S12--
O2B1S2(V) 0.445
O2B2S2(V) 0.335
O2S21(mA) -0.586
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 2852
MAF(g/s) 20.30
O2S B1S12--B2S12--
O2B1S2(V) 0.525
O2B2S2(V) 0.255
O2S21(mA) -0.293
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 2788
MAF(g/s) 20.12
O2S B1S12--B2S12--
O2B1S2(V) 0.545
O2B2S2(V) 0.395
O2S21(mA) -1.270
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1181
MAF(g/s) 5.18
O2S B1S12--B2S12--
O2B1S2(V) 0.655
O2B2S2(V) 0.695
O2S21(mA) -0.441
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 759
MAF(g/s) 4.39
O2S B1S12--B2S12--
O2B1S2(V) 0.555
O2B2S2(V) 0.345
O2S21(mA) 0.098
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 893
MAF(g/s) 4.81
O2S B1S12--B2S12--
O2B1S2(V) 0.770
O2B2S2(V) 0.790
O2S21(mA) -1.953
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1532
MAF(g/s) 5.66
O2S B1S12--B2S12--
O2B1S2(V) 0.195
O2B2S2(V) 0.100
O2S21(mA) 6.543
------------------
FUELSYS2 OL-Drive
FUELSYS1 OL-Drive
RPM(/min) 691
MAF(g/s) 3.74
O2S B1S12--B2S12--
O2B1S2(V) 0.045
O2B2S2(V) 0.035
O2S21(mA) 4.348
------------------
FUELSYS2 OL-Drive
FUELSYS1 OL-Drive
RPM(/min) 705
MAF(g/s) 4.64
O2S B1S12--B2S12--
O2B1S2(V) 0.025
O2B2S2(V) 0.020
O2S21(mA) 4.738
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 654
MAF(g/s) 5.81
O2S B1S12--B2S12--
O2B1S2(V) 0.030
O2B2S2(V) 0.035
O2S21(mA) 0.293
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 611
MAF(g/s) 5.09
O2S B1S12--B2S12--
O2B1S2(V) 0.065
O2B2S2(V) 0.070
O2S21(mA) 0.684
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 645
MAF(g/s) 4.99
O2S B1S12--B2S12--
O2B1S2(V) 0.125
O2B2S2(V) 0.100
O2S21(mA) -0.441
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 582
MAF(g/s) 5.09
O2S B1S12--B2S12--
O2B1S2(V) 0.660
O2B2S2(V) 0.160
O2S21(mA) -1.711
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 614
MAF(g/s) 5.09
O2S B1S12--B2S12--
O2B1S2(V) 0.855
O2B2S2(V) 0.855
O2S21(mA) 0.344
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 630
MAF(g/s) 3.61
O2S B1S12--B2S12--
O2B1S2(V) 0.815
O2B2S2(V) 0.690
O2S21(mA) 2.246
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 657
MAF(g/s) 4.04
O2S B1S12--B2S12--
O2B1S2(V) 0.045
O2B2S2(V) 0.040
O2S21(mA) 1.320
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 664
MAF(g/s) 4.12
O2S B1S12--B2S12--
O2B1S2(V) 0.050
O2B2S2(V) 0.050
O2S21(mA) 0.930
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 627
MAF(g/s) 4.04
O2S B1S12--B2S12--
O2B1S2(V) 0.040
O2B2S2(V) 0.035
O2S21(mA) 1.613
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 651
MAF(g/s) 4.07
O2S B1S12--B2S12--
O2B1S2(V) 0.040
O2B2S2(V) 0.035
O2S21(mA) 1.516
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 642
MAF(g/s) 4.04
O2S B1S12--B2S12--
O2B1S2(V) 0.040
O2B2S2(V) 0.030
O2S21(mA) 1.809
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 635
MAF(g/s) 4.09
O2S B1S12--B2S12--
O2B1S2(V) 0.045
O2B2S2(V) 0.035
O2S21(mA) 1.367
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 957
MAF(g/s) 16.88
O2S B1S12--B2S12--
O2B1S2(V) 0.830
O2B2S2(V) 0.860
O2S21(mA) -3.957
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1721
MAF(g/s) 25.22
O2S B1S12--B2S12--
O2B1S2(V) 0.800
O2B2S2(V) 0.740
O2S21(mA) 0.195
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 825
MAF(g/s) 5.37
O2S B1S12--B2S12--
O2B1S2(V) 0.065
O2B2S2(V) 0.055
O2S21(mA) -4.641
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 2003
MAF(g/s) 51.87
O2S B1S12--B2S12--
O2B1S2(V) 0.670
O2B2S2(V) 0.620
O2S21(mA) -0.977
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 2803
MAF(g/s) 62.28
O2S B1S12--B2S12--
O2B1S2(V) 0.710
O2B2S2(V) 0.595
O2S21(mA) -0.441
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1564
MAF(g/s) 6.06
O2S B1S12--B2S12--
O2B1S2(V) 0.795
O2B2S2(V) 0.650
O2S21(mA) 2.395
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1260
MAF(g/s) 7.53
O2S B1S12--B2S12--
O2B1S2(V) 0.065
O2B2S2(V) 0.075
O2S21(mA) -1.125
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 955
MAF(g/s) 4.81
O2S B1S12--B2S12--
O2B1S2(V) 0.875
O2B2S2(V) 0.865
O2S21(mA) -0.488
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 653
MAF(g/s) 3.19
O2S B1S12--B2S12--
O2B1S2(V) 0.580
O2B2S2(V) 0.825
O2S21(mA) 0.148
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 588
MAF(g/s) 8.03
O2S B1S12--B2S12--
O2B1S2(V) 0.050
O2B2S2(V) 0.065
O2S21(mA) -1.711
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1196
MAF(g/s) 19.39
O2S B1S12--B2S12--
O2B1S2(V) 0.895
O2B2S2(V) 0.880
O2S21(mA) -0.098
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 1097
MAF(g/s) 4.90
O2S B1S12--B2S12--
O2B1S2(V) 0.930
O2B2S2(V) 0.875
O2S21(mA) 4.641
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 582
MAF(g/s) 3.61
O2S B1S12--B2S12--
O2B1S2(V) 0.035
O2B2S2(V) 0.035
O2S21(mA) 2.980
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 560
MAF(g/s) 4.26
O2S B1S12--B2S12--
O2B1S2(V) 0.045
O2B2S2(V) 0.055
O2S21(mA) 1.270
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 615
MAF(g/s) 3.11
O2S B1S12--B2S12--
O2B1S2(V) 0.025
O2B2S2(V) 0.025
O2S21(mA) 4.395
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 644
MAF(g/s) 3.28
O2S B1S12--B2S12--
O2B1S2(V) 0.035
O2B2S2(V) 0.030
O2S21(mA) 0.832
------------------
FUELSYS2 CL
FUELSYS1 CL
RPM(/min) 653
MAF(g/s) 4.04
O2S B1S12--B2S12--
O2B1S2(V) 0.055
O2B2S2(V) 0.060
O2S21(mA) 0.539
------------------

 

I had to read your entire post, again! I have no idea what readings are good or bad for the MAFS right now but I do agree with Ross, I think you have a vacuum leak. At this point I would take your time and go over the entire intake and check for leaks, I would also check the breather ports and lines back to the TB for leaks. For example I reinstalled my intake line and bolted it down to soon find out that I mounted it incorrectly on the TB and it was leaking. Pulled it off, cleaned it and used WD-40 on the lip that allowed it to slip into place properly. I think you need to check the vacuum lines again!

I would also clean and reinstall the plugs on the MAFS & TB and see what takes place. Look them over for any loose or bad connections.

 

ditto for me finding vacuum problems after several checks when I thought I was careful.

 

i found it. It was a vaccum problem. The injector that mechanic changed was not seated down properly. You could see the o-ring sticking out.

 

Kudos to you!

 

So - mechanics are human, too, and can make mistakes,

 

Right, however after I changed the injector and it was still running poor I asked him to look at it again (and paid $100) just to be told it was the o2 sensors.

 

Well, I troubleshoot control circuits for a living, and when two or more problems exist at the same time, it is always much more difficult to find either of them. In this case, though, it seems he caused the problem while changing the injector. As to the real problem, I would not be so sure he is right about the sensors. Obviously, neither could I be sure he was not! Do youhave data , like traces of the sensor voltage, or codes that indicate bad O2s? I do not believe drivability problems with no codes usually are a result of bad lambdas.

 

Sensor voltages are on the previous page. So far the problem has not come back. Only time will tell if thats what it is.

 

redghost
Actually you only posted 3 lambda readings per capture, and there are four sensors. Maybe you have a cut and paste error. Anyway, they seem to be cycling, but it is hard to tell if they are "good" or "bad" without a chart to see what is going on versus time
As I recall, the original problem was shaking, with a misfire noted for cylinder 3 and occaisonally 6. That is (1)3 and (2)2, which are adjacent in the firing order. I suspect you had a misfire in (1)3 and it can be misidentified with adjacent cylinders by the missfire detect circuit. The other problems occurred after the injector was installed with a leak. SO... I believe either you had gotten the plugs damp, or you had a bad plug, or a failing coil. Or maybe not!