Just bought2005 Volvo s40 2.4i. It shows the check engine light and it stalled at 2 times in at stop signs. I sent it to Jiffy Lube and they were kind to check the cause for me. The code read as follows: P0101 MAF or VAF Ackt malfunction. what sholud be the solution to this problem? the oil was change today.

Basically what this means is that there is a problem with the MAF (Mass Air Flow) Sensor circuit.

The simplest thing to do is to reset the code and see if it comes back. Then start with the cheapest, easiest repair procedures:

• Inspect for the following conditions:
  An incorrectly routed harness--Inspect the harness of the MAF sensor in order to verify that it is not routed too close to the following components:
  - The secondary ignition wires or coils
  - Any solenoids
  - Any relays
  - Any motors
• A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor.
• A wide open throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 6-12 g/s at idle to 230 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
• The barometric pressure (BARO) that is used in order to calculate the predicted MAF value is initially based on the MAP sensor at key ON.
• When the engine is running the MAP sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated MAF value to be inaccurate. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 103 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude.
• A high resistance on the ground circuit of the MAP sensor can cause this DTC to set.
• Any loss of vacuum to the MAP sensor can cause this DTC to set.

First thing to do is clean the mass airflow sensor. The sensor is somewhere on the airhorn as the air approaches the intake manifold. It has a connector on the outside and of the intake hose or aluminum horn and pokes into the airstream. The sensor element itself is a small wire and is very delicate. Use electrical parts cleaner that you can get at radio shack or the auto parts store and spray it down good. Put the hoses back together and see if it helped. If not, we can explore the VAF, but I will have to read up on that one.