1999 Avalon hot start issue

[E30M42]

A few months ago I noticed that the fuel mileage was decreasing and the car finally threw a CEL for an o2 sensor. I replaced all of the o2 sensors and that is where the problems started. The very next day I started it up after it was already warmed up and drove down the street. The first stop light I came to the idle dropped and when I went to take off from the light nothing happened when I gave it some throttle so I gave it more throttle and it stumbled like it was about to stall and then backfired. after a few seconds the rpm's came back up and it ran fine for the rest of the drive. It now does this after every hot start. Anyone have any ideas as to the broblem, any information would be greatly appreciated.

[robcam13]

mass air sensor may be dirty

[E30M42]

I did some more testing and it is not the maf sensor and it is not the coils. Any ideas?

[fourwheeler]

the back firing may be due to a vacuum leak. what brand of O2 sensors did you put in? is the IAC causing your poor idle? how are your spark plugs, wires, air filter, fuel filter? is there a caliper slightly seizing? are your wheel bearings getting bad? All may contribute to poor mileage or idle/performance issues.

Also, how did you rule out your mass airflow sensor? Did you clean it?

[E30M42]

It has no vacuum leaks, I used denso o2 sensors, I have not yet ruled out the iac, I have replaced the plugs, wires, coils, air filter, fuel filter, and igniter within the past week and it still has the issue. I know for a fact that the poor mileage was from the bad o2 sensor. All sensors have been tested and monitored with my Snap-On MODIS scanner and I have logged data with my Launch CRecorder2. The misfire only happens after after a hot start.

[bob2]

replace the crankshaft sensor.