Just joined the forum and it is really a good site. I am trying to help my neighbor with his 2001 Prerunner with 3.4 l.His check engine light is on. The local garage looked at it and told him to not worry about it, that it was the O2 heater circuit and not a big deal. I have a scanner and do most of my own work so my neighbor asked me to take a look. First check had P0300-random misfire,P0303-Cyl #3, P0306 Cyl #6 misfire and P1135 Air/Fuel heater circuit response fail. Cleared the codes and restarted the engine. Code P1135 came back on immediately. Drove around for a little while and monitored live data. Fuel code fails and stays in Open Loop mode. Fuel short term trim level stays at zero. If code P1135 is heater circuit, I thought that was for initial start up and once engine reached operating temps was no longer a factor. Engine never went to closed loop and misfire codes did not return. I dont think the O2 sensor will even start to work until engine fuel goes to closed loop. I like to diagnose the problem before buying parts. Any expert code readers on the forum that could give me some clues on what to look for? I don't remember what the MAF data was but thought it was high (maybe 8 gps at idle and 22gps driving about 25mph) is that about right? I will be looking at it this weekend and just trying to gather some data. Thanks for any help.