2000 Tacoma 2.7 misfire/stall while driving

I have a 2000 Tacoma sr5 2.7 4wd xtra cab standard 5sp 157,000 miles. I bought it in 2003 and have never had an issue up till now. Premium gas and synthetic oil is all I have ran in it. I got it with 50k when I bought it as a lease turn in. In January 2023 I replaced the complete head assembly because of a burned exhaust valve. I do the work myself as I have 20 years working professionally as a mechanic. Prior to changing the head assembly, I had a misfire. I still have a misfire/stall even after changing the head assembly. It feels like the fuel shuts off going down the road or sometimes it feels like you cut off a single injector. When Accelerating, it has a lull in it. Not to where it misses, but feels like it the acceleration is coming and going, and that's at any slow take off or faster. When it's misfire/stalling on the highway, if you push the throttle wide open, the misfire/stall goes away but you feel the lull in acceleration I spoke of before. Drove it last night and it missed/stalled for 20 miles, turned around after 2 hours and came home and never missed. All it did was the lull feeling at different points in the travel. Whether it's fire or gas (leaning toward gas) I am not for sure. It will not throw a code and the scanner will not show anything. Here is a list of parts I have threw at the truck in an attempt to fix this issue to no avail. Here is everything from the beginning.

1. Complete head assembly with cams and valves
2. Coils
3. Plug wires
4. Spark plugs
5. TPS sensor
6. Cam position sensor
7. Crank position sensor
8. MAF sensor
9. EGR valve
10. Fuel pump
11. Fuel filter
12. Fuel pressure regulator
13. New Fuel injectors
14. ECM
15. New upstream O2 sensor
16. New ignition switch, not the tumbler, the electrical part
17. New gas cap
18. New air filter
I also replaced the thermostat, put on a new exhaust manifold, and cleaned the throttle body throat and butterfly. There are no vacuum leaks. Every plugin I pulled loose has went back with dielectric grease. I also pulled every fuse, and relay, checked them and went back with dielectric grease. I have checked for broken wires in the harness and rubs etc. I have went through 2 sets of injectors. first a reman set that was crap. 2 of them did not work, and now the new set I bought. I'm getting pretty deep in this thing moneywise. I'm bout ready to pull the radiator cap off and drive a new one up under it and put it on. When it sits and idles, it feels like you're in a brand new one sitting on the showroom floor. Runs great. Any good advice would be helpful. What have I missed??

 

Well when nothing seems to work its usual a small but largely important detail overlooked somewhere that is often caught with a fresh set of hands on it..hard times and desperation may call for a trip to the Stealership just to be done with the problem..overpriced at 1st glance but well worth it if they can fix the problem..I rather never go to the Stealership but at this point what else can be done..

 

I'll pass on the dealership. I worked at those myself for years. Plus the truck is as old as some of the mechanics there.
All they're going to say is Bring it back when it starts throwing a code. They're not going to hunt a problem because it doesn't pay well to hunt a problem.

 

Have you done a compression test?

 

I second the compression check because it sounds like a load issue and you've handled the fuel side.

The other thing that I would do is inspect the injector wiring to see if something is chafed. I would also confirm that all the grounds are good in the injector circuit.

I had a problem with a Dodge Caravan once that resulted because a mechanic back probed a wire and didn't reseal it within the loom. It took years but it corroded at multiple places within the ground wire. The incident occurred before I owned the van so I didn't have the history. Took me a couple of hours to track it down, but it was ultimately a cheap repair.

I'm not saying this is the case for you, but it's worth the time required to cross it off of the list.