C70 surging RESOLVED, bad off brand MAF

[jimmy57]

I don't have VIDA at home so I can't quote exact parameter names but there is a throttle position parameter you can monitor.

[kwma01]

I have checked the TPS in the past and it seems very flat. Actually Graph 2 above has the accelerator pedal position shown as a black line. It is very flat throughout the problem.

I just ran another test where I disconnected the wastegate and blocked it in the open position to essentially take the Turbo out of the equation. I still had pulsing when I went up a long hill. Unfortunately my computer was dead and I could not take any readings. I will let my computer charge and take readings on the ETM and report back a little later.
Thanks again
Wade

[kwma01]

So, After charging the computer I went out for a test drive and charted all of the readings for the ETM. I was surprised to see that the accelerator position was different from the throttle position. The graph showed the accelerator position very flat and the throttle position readouts were all pulsing. This makes me think it may be something going on with the ETM.

I dug a little deeper and plotted the O2 sensors vs the MAF and the throttle position. It looks like either the O2 sensor or the MAF is actually starting the pulse. It is then picked up by the throttle which results in the engine surging.

Any thoughts?

I cannot get a file to attach right now. i will try to post the image in a little while.
Wade

[jimmy57]

Accel pos is the pedal and the throttle pos is the actual position of throttle blade.
The O2 will pulse with throttle as will MAF.
ETM would be the most likely suspect. You could un plug MAF and drive it to see.

[kwma01]

I will try disconnecting the MAF today and see if it makes a difference.
If you look closely at the graph you will see that the pulses start with the MAF (or O2 sensor). I agree with you that it is probably the ETM but it is odd that everything seems fine right up to this moment.

[jimmy57]

The O2 sensor is supposed to oscillate. If you graphed short term fuel trim you'd see that STFT and O2 effectively chase each other. O2 goes rich and STFT goes down, O2 goes lean and STFT goes up.

MAF signal has some play in throttle control but there is no failure history I know of that makes MAF oscillate but there is HUGE history of ETM failing that makes MAF signal oscillate as this is the excat nature of throttle pulsing changing air flow and airflow changes making maf signal vary. MAF varying causes rapid O2 sensor oscillation. Normally O2 would sweep so fast.

[kwma01]

Thanks for the detailed info. I agree that it is probably the ETM. I was hoping to avoid that expense.

FYI
I disconnected the MAF and everything ran great. I know that this puts the car in limp mode but i do not know if that would make changes that would keep the ETM from pulsing.

I will try an old MAF sensor that I have and see if it makes any difference.

Thanks again for your help.

[kwma01]

Well, I can't explain why it worked but I can definitely say that the new MAF fixed the problem. I drove the car for one day with the MAF disconnected and everything was good but it was in limp mode. I then hooked up a different MAF sensor and it continued to operate without any issue.

The first MAF was an aftermarket replacement that I changed about a year ago. The new MAF is an original Bosch sensor.

I do think the ETM has a minor issue because it runs rough when it is first started and it is the original ETM with the white label.

I will drive the car with the new MAF for a while and post if anything else comes to light.

Thanks very much for the help
Wade