My 2001 aztek will run for roughly 20 minutes the stall and won't start again for at least another half hour . It was towed to a mechanic who said he hooked it to his machine and nothing came up as wrong and it ran perfectly for him...got it back and it did it again. the check engine light flashed the first time it stalled out but not the second any ideas?

P0171 and P0174 are telling you that each cylinder bank is running too lean. P0300 is telling you there is a misfire, possibly caused by the other codes. This is why the engine is running rough.

change the fuel filter and check the fuel pressure

It's either overheating or too much fuel being supplied, aka flooding.

I also have 1996 Maxima SE and had same problem. After several months of searching and asking around, I was able to fix the problem by replacing the Mass Air Flow sensor. I replaced with aftermarket MAF and paid $80 with lifetime warranty and the car runs better with better gas milage.
To replace the part takes less than 30 mins., I would recommend replacing the part as maintenance. Otherwise, you can take it to a mechanic and they may spend hours trying to troubleshoot your problem. During my research, there are so many different things that could cause the car to stall and ride rough. I am NOT a mechanic and take my advice for what it is worth and replace the part. It will be less expense if it fixes the problem otherwise you'll need to take to mechanic. They will charge you at least $400 to $500 for an half-hour job.

Good luck. I know how frustrating it can be with repairing the car cost more than it is cost.

Maybe it's not running lean. Maybe it's misfiring. Since you put in new fuel parts and that didn't help, maybe there is an ignition component that fails when it gets hot. A bad coil can do this, also the igniter-rarely, admittedly, but you could have it tested. When it stalls and won't start, if you check for spark and find none, it would confirm an ignition problem.
I hope you find it. Post back and let us know.

Just my opinion but it sounds like a fuel pump issue. When the pump gets hot it stops and after you tow it in it has cooled off by then. Tell someone to check the fuel system first. IE: fuel pressure.

try replacing the fuel regulator,that would make it get too much fuel and the code for o2 sensor will come on saying too lean or too rich fuel mixture,and it would run rough

probably the timing belt broke, there should be inspection in the cover or the top half should be removable for inspection

Change your fuel filter first.
If the problem is still there your fuel pump is going bad.

hi
as we say the main causes is CKP sensor but you can't test it in this case because of interments fault of it when hot only
it is electromagnetic sensor have a coil and magnetic core

about ECT
it is electrical thermo resister have tow wire
1st is the ground
2nd is the 5 volt from ECU drop down with temperature increase
I WISH I WAS HELPFULLY TO YOU
I READY FOR MORE ASK