G'Day
I have a 1999 x308 4.0 v8 NA

After 20 min drive, it was needing to rev higher to change gears.... seemed to lean

Then after 30 min , i stopped with the car, on restart it barely started and twice died/stalled
was able to get home, I initlally thought maybe it was old fuel, so i filled it up with fresh fuel, but same problems later on in day, was rough, but for 90% of the time it was smooth.
It Hesitates with throttle initially ,wants to die, then all ok on freeway.

OBD2 said P0101... this is MAF sensor (ARF Air Flow ratio)
in real time OBD2 data i noticed it tried to stall again, by itself with no throttle and "Vacum /Boost " measure went from +4 to -18 Hg, and air fuel ratio played up and down.

So is this a Vacum problem causing AFR P0101 error, or other way around?

I Will clean MAF sensor but it is 2 years old..... I cant see how MAF problem would make Vacum/Boost swing so much with no throttle. correct me if im wrong.

So Where would such a large Vacum leak reside to cause it to stall??

Best regards
Peter
Sydney Australia

 

The pin connection on the TB could have corrosion on it, a known event. Try unplugging the TB connector, turn on the car, it should go into a default and give you level fuel trims. See how the car drives for a short distance. The default is designed to get you off the road in case this happened on the highway. If it drives descent, then most likely you have your culprit. Try cleaning the pins and check for any broken wires. Corrosion just doesn't corrode, it'll eat through the metal. After cleaning, reattach, clear the code and restart.

If you clean your MAF, use a MAF only cleaner. But expect to replace it, its a 50/50 shot.

Something else to check is the cam cover vent tube attached to the intake tube, be sure its not clogged as well as make sure your air filter isn't clogged.

When did you change your fuel filter last...this may not be just a single issue, but a few little ones as well

The connection at the bottom right of the TB neck is a good place to start. Its a rigid line that is fitted into it via a slip ring. The circle to the right is the one I'm speaking of, but check both.

 

hello high horse
I will do as you say and check and clean it all.
Im just surprised that the car died 2 times upon restart as that would imply a big vac leak.
Hopefuly it is this MAF agian... i know it is not OEM as i changed it 2 years ago, may have to change it
once more.

Would a large VAC/boost realtime fluctuation as i observed on my OBD2 reader , cause a MAF P0101
error?... or is a vacuum leak a seperate error code??
Appreciate your advice
Peter

 

All the above, but also clean the throttle bore and plate (gently); check that no pins in the MAF connector are bent; then, if your OBD reader can read engine temperature. Here in the upper latitudes we find that the engine temperature will often go bad (not read the water temperature correctly) as the weather goes from hot to cold (and in OZ, vice versa). Going to hot weather your system may still be enriching the mixture for a cold start well after the engine is warmed up. The data feeds through the MAF to the ECU. Gives the feel of an over choked motor.

 

+1 for Jim's recommendation as well.

As for the vacuum leak, it never hurts to check for them. It may not be a large one and not noticed until acceleration and the ECU noting too much air via the O2 sensors.

I'd do the pin connection first, then move forward.