Codes P0300 and P0128, random misfire?

Okay, thanks for that. It is strange the p0128 comes and goes but obviously p0300 is constant. I also got to thinking. I have never had to put coolant in the reservoir since I been driving if. It is my girlfriend's vehicle, so I asked her if she or maybe her father had ever put any in and no, not a drop. So, I took the reservoir out and cleaned it. It was disgusting. Like the same nasty antifreeze has been sitting in there for God knows how lone. I made sure none of the lines were clogged or anything like that so yea, definitely must be that the thermostat is stuck closed I'm guessing. I've changed a MAF sensor and thermostat before on different vehicles so that shouldn't be a problem. Does the engine have good power? Well, yes and no. The thing is this misfire comes and goes. I can tell just by the way the engine sounds and obviously performance gets extremely better for a while. Usually in the morning. I drive it to work which is only 5 minutes away from my home and sometimes it will just run perfectly. Check engine goes away. Great power. Everything is fine. Then suddenly you can hear and feel it bog down. Lose power. Takes longer to shift. Even the gas pedal feels different whenever it does this. Sometimes it'll go back and forth like it's trying but something is holding it back is the best way I can describe it. But more often than not especially lately the check engine light stays lit and like I said it's like it's being held back. Like it's only running on 2 cylinders or something. Also it is using twice as much gas than it should be. I know it's probably not the best idea to be driving it and we do try to limit it but it is our only vehicle currently. Anyhow thank you for the feedback and as soon as I can afford it I'm going to get that new tstat and take your advice and get a new MAF sensor. I have an older model f150 and it is notorious for the maf to go out. And I guess the symptoms I had with that are pretty similar to what I'm dealing with now. I just didn't want to guess and throw money at it and be wrong so I thought I'd clean it and even tried testing it with a multimeter. Plus different opinions have me wondering which way to go so thanks again I will report back with progress.

Also, someone told me that my problem could be that I didn't get GM spark plugs. I bought AC Delco instead. Do you think that would really be the reason for my problems? I find it hard to believe but I guess some ignition systems are picky.

My mistake. I was thinking of the old ones I took out. I bought the cheaper ones trying to save a buck. Sorry about the mix-up.

Auto lite APP 5263 are the new ones I installed.

Well, the guy at advance auto showed me list of compatible spark plugs from most expensive to least and I got kind of middle of the road but according to their computers at the store they are correct just a cheaper version. I'm waiting for payday this week. Should have the thermostat and the MAF sensor installed by Friday or Saturday. So, I've looked on the internet a bit and everything, but I mean. Is there a way to test the old MAF sensor to see if it's bad? I found a how to do it online and it involves back probing the wires and using a multimeter. Is that going to be accurate, or I guess what I'm trying to say is would I be able to know for sure if it in fact is bad before I buy I a new one?

All right I guess I will just go with the educated guess and get one. Thanks for your help, I appreciate it. I'll report back probably on Friday and let you know how it goes.

I forgot to mention another major symptom thy I've been having is the car uses twice as much gas as it normally would. Again, I understand it's not the best idea to be driving it, but we've just been going short distances and only when we have to. But I suppose the bad fuel mileage would be because of the misfire? I just thought I'd mention it in case it could be a clue as to the source of the problem.

That's what I figured. Alright I will let you know how it goes. It would be great if that's all it is along with the thermostat obviously. I'm going to try to get it done ASAP, but I've had another run of bad luck. There was a payroll error at work, and I was shorted about $400.00 on my check so I got to wait for that to get fixed before I can afford anything. It's always something may. No luck at all lately. Thanks again for the advice!

Finally, was able to get a thermostat and MAF sensor. I checked my old thermostat by putting it in boiling water. It is working just fine. So, I put it back on. Put the new MAF sensor on and no change. I even made sure to clear the codes before I put it in. I'm still getting the same bad performance. Same code (p0300 is the code that is constant every time I run the diagnostic. Sometimes when I do it, I will get the p0128 and a couple of others. But like right now for instance it's only showing the random misfire). So, I don't know man I'm at a loss. I'm hoping I'm just missing something simple. Any ideas?

So luckily, I was able to get my money back for the thermostat and the MAF sensor p0128 came back. What about the Engine coolant temperature sensor?
Or Intake air temperature sensor?
Either of those a possibility. I still need to do a compression reading by the war. Could it be something as simple as the fuel or air filter? Both are obviously a little dirty, but I mean. The fuel filter wasn't clogged although it is a little dirty from what I could see. And the air filter is a little dirty but not horrible.

Got a buddy who keeps telling me it's the coil pack. And I have read that they are known to be problematic in this engine. I'm all over the place I know. Lol. I got a new fuel filter just because it was cheap so worth a try, I guess.

I've been reading up on how to read and interpret freeze frame data on my OBD2 diagnostic tool and I came across the topic of short- and long-term fuel trim values. This is freeze frame data specifically for the p0300 code. Both short- and long-term fuel trim values are at zero percent. From what I can gather online this means an O2 sensor isn't working. I've already changed the upstream one (the one close to the manifold) although I spliced the new one into my existing plug. (Sent picture to explain) I'm positive I wired it right, but this has got me second guessing myself. I guess it could possibly be one of the other ones but how to tell which one I do not know. Any thoughts on this fuel trim situation? Am I on the right track or not?

Also, I wanted to add that my existing thermostat was working fine, so I didn't change it. Now that code (p0128) has gone away and a new one came up, P0452.

Already told you about the thermostat, I'm sorry.