Audi Repair: 1999 VW CEL Code 1136, mass air flow sensor, mass air flow

Question
I have a 99 VW 1.8T Passat. I replaced my Ignition Control Module and later received the CEL with code 1136. Have since replaced my vacuum hose but code remains. Everyone says it is the oxygen sensor, can anyone assist with this. Thanks

Answer
hello
P1136 stands for fuel, lean condition. Most of the time ( 90%) this is caused by vacuum leak. I have seen broken hoses for secondary Air system, at the solenoid (under the intake manifold), combi valve ( back of the head) or crack large hose right under coolant tank,  also of the manifold.
If all the leaks are fixed , I will replace Mass air flow sensor before replacing any O2 sensor. In last 8 years I have never replace O2 sensor for this fault. With VAS scanner you can check V/B 32 in ECM and if the second reading is HI - you have faulty sensor. If first reading is HI - you have vacuum leaks.
good luck             Greg