Vauxh/Opler Zafira Low Power [No Fix]

No Fix Yet A Good Experience
A friend of mine, running a small garage had requested me to look into a Vauxhall Zafira 1.8L, 2003; Engine code Z18XE. The symptoms were; Extreme loss of power and very poor acceleration in most of the driving time and it can be as bad as a maximum of 20 mph vehicle speed.
The attempts to fix the car went as follows:
* The garage owner (My Friend) had accepted the customers request to replace the Mass Air Flow sensor (MAF) based on a fault logged by the ECU, as he was badly in need of using the car. Two days latter the customer informed the garage that the loss of power was so sever that he was unable to bring the car to the garage.
* On behave of My Friend I went to the customers place and retrieved some DTCs (shown by the attached photo) and based on the symptoms; the one that caught my attention was the P0100 and the live data for the MAF was the next check which was an idle signal of Zero volt (Exactly 0.06V) and a maximum of 2.0 Kg/hr (about 0.55 g/s). This is far from the expected idle value. Basic checks on the wires did show no physical damage, but during this the MAF signal did jump to an acceptable range of 0.6 volt. This enabled me to drive behind the customer and follow him to the garage; were a detailed checks on the wiring sub loom was carried out to confirm no wiring damage. This time the signal voltage stayed at zero and I told My Friend that I don’t know the cause of the symptoms; either more time is given for further checks or We say We don’t know.
* Next day a test drive with no fault carried by My Friend lead to inform the customer that the car was fixed collected and booked for further service work. Days later the car broken-down again and I did volunteer to pick the car and drive (with struggle) back to the garage.
* My next action went in the wrong direction of concluding that the fault is a bad terminal on the signal wire MAF connector. Replacing this with another second hand connector didn’t fix the fault. Next I have used an “improvised” breakout box on this 4 terminals connector (1 from a fused circuit and 3 from the ECU; MAF Signal, Earth and Air Temp Signal). This has enabled me to; 1) see that the idle Zero signal is also in my breakout box terminal and 2) A test of removing the Earth return has caused the MAF signal to jump to a figure above 10 volt.
* Next I have made an unusual action of; Mouth air blowing through the (Old) MAF with the ignition on and saw a clear rise in the signal voltage. While this does not seems scientific enough, this action did confirmed that the Engine running bad MAF signal was not related to the sensor and its wiring. This action was a chance to see the effect of low quality spare parts; The “New” MAF purchased from a local part shop, didn’t show any voltage rise during the blowing.
* Next We went checking the timing belt marks and confirmed OK and My Friend went further to show me that when piston No. 1 TDC come along the Timing marks; This according to his experience of that particular Engine is a confirmation that the actual Cams positions are also OK.
* Next 2 checks; Inlet Vacuum reading was showing an ubnormal gauge position on the Red zone of LATEING TIMING and an Exhaust back pressure (using the O2 sensor 1 port) showed a normal gauge reading; No blocked Exhaust.
* Finally My Friend decided that he has to cut his losses and inform the customer that We don’t know exactly that was the fault.
A touch of Imagination
Had the Job managed in away to have the customers approval for more time; We could have the chance to send the ECU for a Laboratory test . Later I did an internet search to find the likelihood of an ECU fault. A common failure for all 1.8 Vauxhalls with this system type; the problem is caused by the location of the ECU. It is bolted to the side of the engine block and can’t dissipate any of its heat, combined with engine vibration and wild temperature differentials.
Related to this is is an action taken to try to block the neck of the air filter box and confirmed a good sucking action at idle. So why the MAF signal is Zero Volt? One possible answer is; That a faulty ECU can give incorrect Ignition and fuel Injection commands (possibly Retard) and this may cause a resonance/ or turbulence in the induction system leading to the ECU seeing a; Circuit Low MAF input.
Bashar Alqasim

Hello, did you checked MAF signal with a scope and compared against scanner data pid?

No Scope was available at the time of the check, but the Pid/ Live data was exactly like the voltmeter reading of about zero g/s. also another car with a similar engine management system was checked showing 0.6 volt at idle.

So you say the signal you have does not match with air entering the engine !? What you have and should see next, is if the MAF has 12volts and ground using the voltage drop test.
If everything is fine you should make a bypass to the signal wire with the test light connected from battery positive to the signal wire, signal voltage should increase. You must know what you doing or can damage ECU.

The bypass must be with a incandescent light not a LED!!!

The strange thing is that the signal seems matching the air passing through the MAF sensor and this is the only explanation I have for the following: when losing power the Engine run and idling signal in both the voltmeter and the PID is Zero, then when I blow air with the engine off-ignition on (by my mouth) I was able to get 0.8 and above volt. All this is intermittent (though most of the time), as some times the engine runs fine with no loss of power and in this situation the idle MAF signal is around 0.6 volt

If you say the wires are ok, so you must have a bad contact on the MAF plug, ECU plug or ECU internal pins. With engine running and checking voltmeter, move plugs and cables to see if same thing happens, check power/fuse to the MAF for bad contact...very common is bad pins contact on plugs!
The issue must be there to test or make it happen. Do not guess, test!