I have a 2005 lr3 that I have been trying to hunt down an issue. I am getting a p0316 and cylinder 4 p0304. The truck is stumbling upon start up and throughout the power band. In the last year I have replaced the throttle body thermostat housing and thermostat. Maf sensor air filter as routine maintenance was also replaced.
recently in the past few days cleaned maf with maf cleaner.
changed all plugs with OEM plugs , changed all 8 injectors with autoline replacements. Cleaned egr. I also swapped plug and coil pack one and 4 to see if the problem persist. Still there so I did a compression test on cylinder 4 results 175. Did 3 and it was 175 and did 1 and it was 175.

Weird thing is I don’t get a check engine light but I get codes when I put my generic reader on it.
Truck has 140k. I dont want to take it to the dealer but I may have no choice. It runs just fine on the highway above 60. . Just stumbles at idle and low speeds and runs like crap . I put a can of bg44 in it and surprisingly it ran well with no symptoms but when that chemical burned off back to misfire and stumbling. Where do I go from here.

** just took the truck out about 10 min ago 65 degrees outside did a couple per to the floor runs and got yet another code. P0628 low fuel pump circuit. Yet I still don’t have a cel I. The dash or a check engine fault code through my generic reader. The dash is visually clear of codes

 

I would swap out the injector on that cylinder

 

sorry I forget to mentioned I changed all 8 injectors with auto line injectors.

 

Would a cat about to go faulty cause this