ok so i have an 04 with 101,xxx. Mazda speed cold air intake with K&N filter, Racing Beat exhaust. I have been having problems with my engine misfiring on cold start ups only with which i would start it up cold and it would idle hard and misfire for about 25 seconds then return to normal operation. The car would run fine after it warmed up. The CEL i kept getting was "Cylinder 2 misfire". I replaced all coils, wires, and plugs yet this issue continued to happen. I just recently hooked up the fuel pump to a gauge and it read fine( just under 60psi). About a month ago I started to get the P0171 code while i was driving. It would come on for about 2 days then go off. then it would come back on after like 2 drive cycles. Now within the past couple days i figured out how to prevent it from misfiring on cold start up by turning the ignition on and waiting about 15 to 20 seconds before turning it over. It hasnt misfired since i started doing that (awesome, maybe the ecu just needs to refresh every time i cold start the car). The P0171 code has not come on for a while but just came back on today as soon as i filled my car up. WTF is wrong with my car??? I think all this started coming up around the time I started using Shell's V-Power premium gasoline. Could this be an issue? Or am i so far off for thinking that and it is just the MAF, O2 sensor, or compression leak. Once i get some extra money i would like to go get a compression leak test done but before i go spend the money i wanted to see if anyone could help me diagnose this problem. I have been having this problem for months now and cant seem to figure out why it is doing what it is doing. I have read around everywhere but it seems that i have a pretty unique set of problems. From what i have been reading on it seems like i have narrowed it down to three possible problems: the MAF is bad(already tried cleaning it), bad O2 sensor(s), or a compression leak. This problem has been having me smashing my head against the wall for a while now but i love my car and i just want it to run smoothly with no CEL's. Any words of wisdom will be appreciated. Muchas Grassy ***

 

https://www.rx8club.com/series-i-trouble-shooting-95/cel-p0171-223935/

Also, when you say you turn the ignition, you're normally firing it up instantly, without allowing the fuel pump to prime up first?

 

No, normally i only let it sit for like 5 seconds before cranking it over. thanks for the link

 

I will take apart the UIM when i get the chance and check for any leaks. I will update after i do this