2004 lexus ls430 both banks are leaning out I have replaced the fuel pump , filter spark plugs and I’ve recently got the timing redone . Yet I still have a rough hesitation and a terrible back fire almost like a 2step system. I have codes P0171 and P0174 I’m gonna try to replace the intake manifold gaskets this weekend and maybe a couple cracked hoses along the way but I’ve been asking around and some people still say fuel pump or maybe fuel pump pressure regulator

 

You can try to smoke test the vacuum system. Have you checked the MAF sensor? Can you check the fuel pump pressure with a gauge? Try the simple first. If you do replace the intake gaskets I would replace the starter while you are there. When you say timing redone do you mean the timing belt? Did this happen before the belt replacement?

 

I bought a MAF sensor tried it and saw no difference, when I replaced the fuel pump it went from feeling like it had no fuel to now seeming like it’s either getting too much air or not enough . But I’m not sure if the fuel pump is good. I’m about to order knock sensors and a starter for when I do the gaskets and maybe try to find an entire new fuel pump assembly . I had the problem prior to doing the timing. I could go rent a fuel pressure tester but I’m not sure what the normal psi should be. I’ve been in a rabbit hole trying to figure it out and I’m going crazy

 

I would definitely get a fuel gauge and start there. Also where did you source the fuel pump and MAF from as well as brands? Did you initially change the fuel pump due to the codes? Especially after COVID there is an extreme amount of absolute cheap junk parts on the market. I would look over all your vacuum lines, especially the breather lines coming from the valve covers. The one that goes from the right side valve cover to the intake is not easy to inspect and usually at this age is cracked or torn. Check your brake booster line, etc. Before throwing more parts and labor at it I would go for more testing.

 

I get all my parts from rock auto I try to only purchase Denso parts but I know the vacuum line from the intake to the valve cover is broken , most other lines looked fine I just had to replace my radiator and spark plugs so I was checking over all that in the process . This morning I had just under a quarter tank in my car and it was barely having any response to throttle but I filled it up and it felt to have a good bit more power but still if I try to fill throttle it just starts back firing and popping

 

might want to do a compression test ?