This is an interesting case. The other day, this car came in for a cam belt and water pump job. After the work was done, the customer collected the car, and after 2 days, she called me and said she was having problems with the car, The engine was running after she started it, but she could not rev the engine. She puts her foot flat on the accelerator, but nothing happens. She thought I did something wrong with the cambelt job. I went to her and plugged in my scanner, and I got the following fault: P061D-60 Internal Control Module Engine Air Mass Performance.
I told her that that fault had nothing to do with replacing the cambelt. I unplugged the air mass sensor, and then I could rev the engine, performing a typical basic test for the airmass and airflow sensors. I took the car to my workshop, and once there, I plugged in the sensor again to test it with the picoscope, but now the car starts and the engine is revving, and according to picoscope, all is well with the sensor, can also be observed through the scanner. see image
Airmass Sensor
Something worries me because I don’t understand how an airmass sensor can suddenly work properly. I have done nothing to it; I have removed or cleaned it. I told the lady I wanted the car checked again the next morning because now, later in the day, the car seemed to be okay. The next morning, when I start the car, the engine will run but will not rev. I tried starting it again, but this time with the voltmeter checking the voltage drop at the battery while starting the engine. Well, what happens is that the voltage drops to 8.3 volts, and you cannot rev the engine. So I use another car to connect good, strong jumper cables to both batteries. The batteries are connected in parallel, and I have not started the other car. I start the Figo again to see what happens now with more battery power. The voltage has dropped to 10.5 now, and the engine is now revving. It looks like if the battery on the Figo is bad or flat and the voltage drops below 9 volts while you are starting the engine, the ECU blames the airmass sensor, and there is a warning light on as well. I forgot to mention it before. But if the voltage is above 9 volts, then all is well. The Ford Figo doesn’t like bad/flat batteries. A few years ago, I had a Ford Fiesta 1600 Duratec engine, and the battery was also bad, but in the Fiesta case, the engine did not run at all, the battery must be in good condition to make the ECU happy to run all electronic components otherwise, it keeps some sensors in the off position or they might perform badly.