Stalling at idle when warm P0102

goldxc70 · Post by **goldxc70** » 26 Mar 2021, 10:45

XC70, MY '04.
First happened a couple of weeks back: accelerating gently on open road, "reduce(d) power" message briefly appeared, engine cut out, pulled out of traffic and tried to restart but nothing. After leaving it a while to cool down (maybe 20 minutes), it restarted normally and I drove home. Later that same day, it started normally but when I tried to back out of parking space, it stalled repeatedly. Left it overnight and it started fine the next day. Checked all the usual things and cleaned the MAF with sensor cleaner. OBD reader gave me a P0102 code and nothing else. After resetting it, I get the same code immediately but it runs fine. Checked MAF connector and 12v, 5v and GND all check out. MAF reading seems odd (jumps between 0.25 and 0.5 g/s) but this could be the budget tools I'm using. The fuel pump and filter are relatively new having been changed a few years back. My car doesn't have a fuel pressure sensor on the rail.

I have a new MAF and happy to try that but wanted to know if there is anything I should look at before doing that.

93SCMax · Post by **93SCMax** » 26 Mar 2021, 11:59

Bosch/OEM MAF only.

goldxc70 · Post by **goldxc70** » 26 Mar 2021, 12:10

Original is Bosch and so is the new one (which I'm planning to install later). In case it wasn't clear in my OP, there are no other codes being shown at all.

Post by **oragex** » 26 Mar 2021, 12:32

Your 2004 had the CEM water ingress, you can also look from underneath the dash with a flash light

goldxc70 · Post by **goldxc70** » 26 Mar 2021, 17:58

I guess sometimes it actually is the MAF Sensor. It certainly seems to have been in my case.

Post by **abscate** » 27 Mar 2021, 02:10

The MAF reading jumping at idle is a good tip off, if you a trust the tool, of course

This is also a time where stopping the engine , unplugging the MAF . And restarting would have improved the idle. The problem with that approach is that same diagnostic points to many possible causes, not just the MAF

Post by **RickHaleParker** » 27 Mar 2021, 11:18

goldxc70 wrote: 26 Mar 2021, 10:45 Checked all the usual things and cleaned the MAF with sensor cleaner.

Possible source

Flow too high:
- short-circuit to supply voltage in the signal cable
  open-circuit in the ground lead
  defective sensor
Flow too low:
- Air leakage
  contact resistance
  Contaminated throttle body (TB).
  short-circuit to ground in the signal cable
  open-circuit in signal cable
  open-circuit in power supply cable
  Defective sensor

goldxc70 · Post by **goldxc70** » 31 Mar 2021, 17:56

Five days later and car is running very nicely after swapping out the old MAF for a new Bosch. When I compare the scantool graphical outputs, it's very clear that the old MAF was faulty: air intake was not changing consistently or at all with changing engine speed. When it did change, MAF was capping out at a fraction of what it should have been, 0.5g/sec instead of 12 g/s.