Shop Peugeot Oxygen Sensors

Hello all, my car failed the MOT last week on a small piece of welding .The garage had to remove the petrol tank to do the weld as it was very close to the hole,they also fitting me a new rocker cover gasget.It passed the MOT but shortly after I picked the car up about a mile towards home the engine management light came on for about 10 seconds then went off,i have driven the car about 15 times since then and each time after about amile or so the lights comes on for about 5 to 10 seconds the car is also running a bit rough ,and also a bit shaky whiles idling at 900 revs went the car is warm .I have driven the car for 9 years and the light has never been on before and the car was running fine before it went in the garage.I took it back to the garage and they charge me to run some test and told me it was contamination of the lamder sensor because my car is burning a little oil,they cleaned the sensor for me and told me it should be OK but its not.Are they pulling the wool over my eyes as the was running fine before they had it for the MOT repairs.Has anybody an idea what it coulld be ? It a 1994 Peugeot 106, 1.4 XSI ,UK car IT DONE 120,000 miles and has a full service history. Thankyou ,regards Martyn.

hi you need to have the vehicles computer scanned for diagnostic trouble codes and then post the results here so we can be more help to you , if your vehicle has 120000 m on it , it is probably due for a new oxygen sensor (lambda)anyway . if they did in fact have the fuel tank out to perform repairs , did they disconnect all the fuel lines ?more importantly did they refasten everthing properly? did they install a new fuel filter at this time ? i would . also you might want to pull the spark plugs out and thouroughly inspect them , check for evidence of oil burning . also inspect the area around the rocker cover that was removed , make sure all vacuum lines and anything else removed to gain access is in order . so when you get a chance post the codes and we will get back to you k ...hope this helped you a bit, good luck , talk to you later ..........Todd from the hammer........