Audi Repair: Faults 1136 & 1138/ collant leak, mass air sensor, audi a6 quattro

Question
I have a 99 Audi A6 quattro (1/1999) w 100k miles.  I am getting faults 1136 and 1138. I have repaced the Mass Air Sensor but the faults are still there. Do you think I could have a vacuum leak or do you think it could be the Oxygen Sensors.

Also, I want to replace my engine coolant sensor (I got a fault suggesting that it may be bad).  I have the Bently manual but I am still having a difficult time comparing the pictures and locating it on my model. I believe it is an easy DYI project. Any suggestions?

Answer
hello
I guess , you have 2.8 engine . 1136 and 1138 are for system too lean, I will check for any vacuum leaks first. O2 sensor can be check or watch using VAG and this will tell you if they OK or not.
Coolant sensor is located on the back of the engine , on the pipe connecting both cylinder heads, more to r/side .
You will have to remove flex air duck from air filter.
very easy to do .
good luck                     pltech