low coolant temp/ 17535 p1127 mult fault code

[s4nchez]

Hello all,

in a bit of a quandry and need to ask for help....
I have a '52 face lift 225 bhp S3. last week i noticed that the temp. coolant gauge was @ 75-80C , had always previously been 90C regardless. Next day the ECU warning light came on so I took the car into a VW/Audi specialist who had the car idling for 1 hour, the temp gauge went back upto 90C. VAG.com threw up fault code 17535 p1127 mult. bank 1 running too rich. An emissions test showed the engine running too lean and power is well down and sounds/feels a bit rough. ECU was reset and fault went. Warning light came on again after 25 miles so took car back in and they loaned me a new MAF to see if that resolved the issue. ECU light back on again.

I have searched for hours to find a possible cause, apart from the MAF could it be a temp. sensor/boost leak? if so, from where?

any ideas/ experiences would be gratefully received
thanks in advance

[s4nchez]

in case anyone else has the same issue in the future......

Engine coolant temp. slowly got to 90C with air-con OFF, but would go down to 75-80C with air-con ON. Air-con diagnostics threw up no fault code, but engine coolant temp readout (51c) would get upto 75C max.

New engine coolant temp sensor/lambda sensor made no difference
but the replacement MAF was not a genuine VAG part (has now been replaced again by a VAG MAF) and I asked for a new thermostat to be fitted. Touch wood problem solved by Gary and Martin @ E B Jones, Liverpool