HELP!

We just spent $600+ on our 02 Sienna to replace the Air Fuel ratio sensor located on the exhaust manifold before the cat. We noticed some loss of MPG and out of no where the engine shot out the code for the Air Fuel sensor. The dealer could not get the sensor out and had to replace the exhaust manifold (ouch!). We got the car back and with no rhyme nor reason the more we drive the car we will get a pop sounds from behind the fire wall. We took it back to the dealer and you would know they could not duplicate the problem! After a week of the dealer playing around with the car we took it back home and the next day our little annoying sound was back. It almost sounds like a slight back fire form the air intake. I tried to find a pattern and at first it looked like when the engine was shifting so I was thinking a engine mount because the dealer told me it was on the side of the fire wall. Well today I opened up the hood and to my surprise it was the sensor on the front side of the engine. Now we are back to the back fire theory because today it popped again this time while cruising between 2nd and 3rd gear. Also we noticed our MPG are going down fast, we use to get @90-100 mile per 1/4 tank now we are at 75 Miles. It also feels like you have to get on the gas more to keep the car moving. We are frustrated with the dealer as I am afraid they will do the old "hey we found you problem and the bad news is it is something different and it will cost you $1,000" because they are using the shot gun approach. My wife is so **** she is ready to torch the car in the dealer parking lot! Any idea's?

Hello,

I hope you had kept the old A/F sensors the service station replaced. I always do that as a protection for myself from possible rip-off at a shop.

The code 1135, 1155 might be wrong, not reflecting the true cause. i.e. your old A/F sensor are most likely just fine.

did you check your down stream Oxygen Sensor behind the catalytic converter. On mine 2002 sienna, I initially got 0420, 1135, and 1155. I replace the A/F sensor 1, but still get 1135, indicating sensor 1 is bad, which can't be true as it is new. An accidental look at the downstream sensor revealed the mount is rusted out, causing the sensor to pop out of the hole, which gives out a backfire sound. After fixing the mount, I put back the old a/f sensor at bank 1, now I only get 1135 just as with the new a/f sensor. Too bad, I can't return it anymore.

However, I still need to find out why 1135 is still on.

So, check it out first. Also a leaked exhaust pipe may cause check engine light to go on.

Good luck!