2003 focus st170. fault code p1131 it is manafacturer specific any ideas, car meant to be in for mot this morning now this bastard has came up

 

just did a google search and it came up with

P1131 Lack of Upstream Heated Oxygen Sensor Indicates Lean - Bank No. 1

 

any ideas gents, one minute it runs smoothly and perfectly then leave it on idle for a few minutes and it starts to run lumpy and is very stuttery when accelerating

 

well your first, im poretty sure bank1 is the first, lamda sensor is indicating lean, so you could change it, i would look for leaks first though

 

Could be the hego/lambda sensor thats knackard. Might fail its MOT on emissions

 

all sorted now, i bought a new lambda sensor and a new set of plugs, it was still the same so i decided to have one last look at the intake system before retitring for the day and discovered a piece of foam covering the maf, the foam is the piece that filters the rocker breather which plugs into airbox, fuck knows how it passed the ait filter though but she is back at full health now

 

Glad its sorted, fook me how did that bit of foam get through?