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fenrisx
02-02-2010, 07:56 PM
So... to start things off. My 4Runner had thrown the CEL last spring, and AutoZone ran the code as pl420. Fast forward to about two months ago, the CEL goes off on its own. Then about two weeks ago it came on again. At the same time the exhaust got really loud, and gas mileage was down to like 5-6mpg.

I took in to the dealership yesterday and than ran it on their diagnostics computer and told me it was throwing P0171 and P135. He said this was because the Air Fuel Sensor had failed, and the other code was a lean code as a result of the air fuel mixture being off. The loud exhaust was due to the rear oxygen sensor bolts being broke, and the sensor was just dangling. So they rethreaded the hole and put it back in.

He also said there was no sign of the 420 code, and also said that sometimes the code readers that AutoZone uses reads codes like the ones I had wrong, and displays them as the 420.

My problem is that five or six times now when I start the car it dies right away. It takes about three times before it stays running... and usually I blip the throttle as soon as it starts so it doesn't die. What would be causing this?

kregg
02-03-2010, 11:13 AM
Throttle position sensor or Mass Air Flow sensor... My 2 guesses

Seanz0rz
02-03-2010, 11:36 AM
id check fuel pressure, idle air control valve in addition to the above. you also have a 99+ so maybe AFM?

MTL_4runner
02-03-2010, 12:36 PM
Sounds like they didn't reset the ECU when they reinstalled the O2 sensor and that was also why you were getting the P0420 code it sounds like (ie there was a massive air leak in the exhaust before the cats). You should pull the negative battery terminal for about 10-15 mins to reset the truck's ECU and see if that doesn't help your situation because right now the ECU is probably confused and in the process of relearning the proper A/F setup.

fenrisx
02-25-2010, 10:15 AM
I went with the 'don't do anything, and see if it will fix itself' method. That seemed to do the trick. It hasn't happened since I posted the thread I don't think.

corax
02-25-2010, 04:30 PM
How did I miss this? Easy - it had nothing to do with the MAF. It had everything to do with the oxygen sensor reading air from outside the exhaust. HO2S (heated oxygen snsr) saw so much O2 that it thought you were running lean as hell, you can get the same thing from a leaking exhaust gasket if it's anywhere near the HO2S.