Taco Stalling/Loss of Power

So I've been having an intermittent issue with my truck where at speed(usually around 50mph and above) it gets a slight hesitation like a skip. I've been somewhat ignoring it until recently when I got some free time and spare cash to throw at it. I have 266k on it and to my knowledge everything is original as far as engine parts goes except:

New plugs and wires about a year ago now I think.... I guess I could throw a new set of plugs in just to be sure.... but I doubt that's the issue considering I had at least 80k on the old set when I changed them last
New fuel filter from O Reilly
AF sensor replaced with Denso part(would've replaced the O2 sensor... I bought it and was going to do it as well..... but the nuts were rusted off and I did it the parking lot of my apartment one night after it cooled down from the lovely Atlanta commute)

Background: Plugs were replaced when I thought my transmission was dying. Also had the transmission serviced then too. Fast-forward a year later to now. I started noticing that right after starting, it would hesitate when first pulling out of the parking lot sometimes and now I've been noticing a sort of lack of power when flooring it(thanks Atlanta) and a skip just at random times at speed while cruising on interstate. So I ignored it because I figured it was a fuel problem and I'd get to it when I could. So I bought seafoam and ran it through. I'm sure maybe helped some, but still same problem.

This past weekend I drove it pretty hard on the way to town to meet my buddy to go fishing and noticed it just feeling sluggish until I got high up in RPM then it sounded a lot better. Got to town, shut it off, hopped in his truck and tore out to fish. Had bad luck fishing and came back. Cranked the truck and it would barely idle. Running horribly. This is when I finally got a CEL. Drove straight to O Reilly and bought a fuel filter since Toyota was closed. Drove home to put fuel filter on.... Got home and realized I had no metric flare nut wrenches.... tried it with SAE set.... got one side off, couldn't get the other.. Said f it and I'd worry about it tomorrow. Was tired from being in sun all day and sore from first week in the gym. Popped code reader in though and had a few P0171 codes and a single P0300 code. Didn't read freeze frame data and cleared them. Fired truck up and let it idle.... sounded fien and by this point had cooled off to room temp for the most part. Drove it around some. Came back, shut it off again. Cranked it up and revved it up in park. BAM there's the CEL again. Same P0171 but no P0300(after reading forums figured out that's because it has to happen twice for the light to come on) Began Googling, Tacomaworlding and watching Youtube. Found a video of a guy (I'll look for it and post the link) who did a really good explanation of exactly what was going on with my truck.... My LT fuel trim was at 39.5% and short term was around 14-15%. I'm in south Georgia btw. MAF looked to be working based on readings and coolant temp was around 180-190 once warm and I watched it increase as engine warmed up, so I'm figuring it is good as well. Throttle position sensor looked to be throwing good numbers too when idling and revving. Started looking for vacuum leaks and found one small hose with a split..... not enough to cause a big enough vacuum leak to screw up the fuel trims that bad. So on to the MAF and throttle body. I had no MAF cleaner, so I just called it a night. Ended up buying a used MAF off a prius(same part number as the replacement from

$89 Toyota 22204-22010 Intake Meter Sub-Assembly

Toyota 22204-22010) for $12 on ebay that just arrived today.

Next day I go to Harbor Freight and buy metric flare nut wrenches and vacuum tester, vacuum hose and MAF cleaner from O Reilly and a double cheese combo from the Dairy Queen. Forgot throttle body cleaner... oh well maybe I won't need it. Go home and change the fuel filter. Replaced vacuum hose, tested vacuum like in the video and deduced that a vacuum leak wasn't my problem based on my fuel trims. So on to the MAF again. Took it out, inspected it only to find a sagegrass seed wedged in the two contacts up inside it. Removed it and sprayed it down with the cleaner. let it dry for a bit while I cleaned the airbox out of boredom. Put it back in, cranked the truck and looked at the fuel trims. Long term still at 39.5% and short term was well into the negatives. Problem solved! After driving it around some, it felt more throaty and didn't have the hesitation or skipping feeling. Long term fuel trim at idle down to around 7% now and short term at 0%. So. Shut it off. Cranked it back up again and drove around some more... this time pretty hard on the 2.5 mile straightaway my house is on. Still felt good... definitely better than before. Drove home, shut it off and cleaned all the leaves and dirt and whatever else was up under the toolbox and went on with my life thinking I'd found the solution.........

This week, I notice the same freaking little studder at speed which caused me to become angry and frustrated and say SCREW IT I'LL PUT UP WITH IT until I got my newly arrived used MAF sensor in the mail today. Thanks to the USPS for consistently being the worst possible carrier for shipping anything larger than a regular envelope.....whatever....shipping was free.


SO, I have decided to try and find this issue, which according to a lot of threads here can be a fun little monkey to play with(and I intend all sarcasm you could possibly imagine when saying that). I called a buddy that does some mechanic work on the side and works on drag cars/trucks for people. He mentioned it could be the crank position sensor or the cam position sensor.... I'm researching those now.... cam sensor looks like something I would just go ahead and replace if I went to the trouble to get to it.... along with a bunch of belts and stuff so I don't really want to look at it if I don't have to because it's behind the timing belt. Crank position sensor seems easier to get to and I'll check it. I also need to check my fuel pressure but it seems to me like there is no easy way to do that... I did find a thread I'll have to re-find that talked about how to install a fuel pressure testing port thing to install on the fuel rail thing and then get a fuel pressure tester thing and put on it and read some PSIs, but I haven't bought either of the things to do any PSI reading since I thought I had my problem fixed. I refuse to pay someone to test my fuel pressure.

****IF YOU'RE STILL READING****
If anyone could direct me to the resistance specs or directions to test MAF, crank position sensor, and cam position sensor, that would be great

I'll keep a running total of things replaced/cleaned/checked as well as what my next steps are below. I hope that wasn't too much at once and makes sense.

Troubleshooting Completed:
- Seafoam
- Drank a beer
- Watched a lot of youtube videos and looked at forums and google
- Questioned existence
- Tested vacuum leaks
- Replaced small vacuum hose
- Replaced fuel filter
- Cleaned MAF sensor
- Running Techron injector cleaner through it for second tank now
- Priced new Tacomas
- Priced new F150s(I know....don't roast me)
- Posted TW thread
- Cleaned throttle body and intake
- Replaced MAF sensor with used eBay one
- Replaced rear diff fluid

Troubleshooting on to-do list:
- Replace rear diff fluid(completely unrelated but I'm doing it this weekend)
- Change out MAF sensor with used one from eBay after cleaning it because why not
- Clean throttle body
- Install new spark plugs
- Check crank position sensor
- Check cam position sensor (maybe)
- Check fuel pressure
- Receive advice from TW thread that can hopefully lead to my problem and solution

 

https://youtu.be/SugtR4KMIDU

Link to the diagnostic video I watched... I know... I'm a youtube mechanic

 

I know it’s a lot guys. But any suggestions other than what I already have? I’m not taking to a shop and if I have to start playing the replace a part game, I’ll be in a 2021 time they roll out.

 

No ideas? At least I know it’s a strange encounter....

Anyway, I changed the MAF sensor out today with the used one from eBay, cleaned the throttle body and entire intake, and changed the rear diff fluid(unrelated but needed doing...and found I needed a new spare tire in the process so win/win)

Not sure if the MAF sensor fixed it or the throttle body cleaning, or if it’s even fixed, but my fuel trims look better now. I was actually running in the negatives at idle. Not sure if that’s a good thing. They did pick back up once the engine warmed up good though...To around 3-5% total.

Drove it down the road a few miles and it definitely felt better and more responsive, but the real test will come tomorrow/this week when driving a longer distance. Spark plugs are cheap and plan on throwing a new set in this week for good measure. Got a little over a year and around 12k miles on the current set. Will update if the problem arises again or not.