Engine surges

[daroutt]

I have a 2001 QX4. Recently the engine has started surging and running rough, even backfiring on occassion. I have replaced the plugs (vehicle has 104K miles), cleaned the MAF sensor, installed 2 new rear O2's and a new cam shaft sensor. (The last two were done before the surging and backfiring started). Also took it to my local Nissan dealer to see if they could help. All they wanted to do was flash the ECM because they said there was an upgrade that needed to be loaded into the computer. Can anyone tell me if the fuel filter and/or fuel pressure regulator are the problem or this an injector and injector pump issue? Any feedback would be appreciated and helpful.

[Infinitiguy19]

Are there any Check Engine Light codes?

What does the upgraded ECU software fix?

[fastpathy35]

My understandiing is that the ecu flash is an idle relearn process. All the vq35 have this problem and its free to have done at the expense of running diagnostics to see if thats the problem...ha! I would go to an auto parts place and see which codes are being thrown (for free).

[daroutt]

Yes there are OBDII codes. They pertain to O2 sensors (open loop) nothing to do with fuel issues. When I clean the MAF sensor and clear the codes they dont come back for a week or so. When they do come back it the same O2 codes. Another "valuable?" bit of info from the Nissan tech that flashed the ECM is to disregard the O2 sensor codes. He advised he replaces the MAF sensor and 9 out 10 times the O2 codes will not come back. I plan on replalcing the MAF sensor, but this surging problem is something new. It really feels like a fuel issue and not exhaust gas. But I'm finding out this is not a "shade tree mechanics car"

[daroutt]

Also, supposedly flashing the ECM was necessarry after installing new O2 sensors. According to the local Nissan service dept. the cars computer cannot relearn the installation of some new sensors. I wonder?????