This looks like a pretty busy sub but I thought I’d see if i can get some suggestions. I have a 2003 Toyota Tacoma Pre-runner with the 5VZ-FE V6 engine. I’ve been having this issue for awhile now, had it at a couple different mechanics and the dealer who all have not given me much to go on.

Symptoms only appear when the engine is hot and has been running/driven for about 5+ miles. On a cold start, everything is fine. Starts right up and stays running at idle.

Then if I drive it for a bit and then shut the engine off, it has a lot of trouble starting while it is still hot. Sometimes it will start, and then stall a few seconds later or after I put it in drive and try to get moving. Also, normally on the highway, if I try to accelerate too quickly it will lose power around 55mph or so and i have to let off the accelerator and ease into it again to get up to speed. It has also gotten to the point where if will sputter on me if I am at a stoplight or in traffic and have been driving for awhile, I have to feather the gas a little to keep it running.

Codes are showing P0300 Random/multiple cylinder misfire, P0302 and P0304 misfires, and P0171 System Too Lean Bank 1

This all seems to point to a vacuum leak, I changed out the air intake boot that was cracking on the ends and it seemed to help a little, but not fully. I changed another couple of vacuum hoses but otherwise haven’t found any myself that look like they could be the issue. I have had the fuel pump changed because one of the mechanics indicated the pressure was low and that should fix it, but it didn’t. I have also had the brake booster replaced, and am wondering if that could be a cause also? I’ve changed the spark plugs/coils, MAF sensor, and I think that’s all I can remember off hand.

The thing that throws me the most (I’m handy but don’t know that much about engines) is that it only happens when hot. After awhile of researching I have concluded it’s likely a fuel injection issue, bad brake booster, or the fuel pressure regulator. Otherwise I’m pretty stumped with my limited knowledge. Any advice at this point would be appreciated.