Hard Starting and Misfire

Had some really good advice here already, hoping for some more.

My 2000 (V6, 280k miles) has been running rough for a while. Bad gas mileage and throwing 02, evap, and lean (P0171) codes. I've fixed a bunch of problems but still have a couple.

Recently along with the codes it started being slow to start (5-8 cranks instead of the usual 2-3) and having an occasional misfire only at idle.

I chased some leaks and replaced the intake hose and some vacuum lines. I also traced a bad evap sensor and replaced, which cured the evap code. I was still getting the hard starting and occasional misfire. Cleaned MAF, no change. The truck runs great at highways speed the issue is only at idle, both in and out of gear.

Misfire got worse on a long drive to where it was totally fine on the highway but when I stopped for gas it was dying at idle. I replaced the coils, plugs, wires and PCV valve. After that it ran perfectly for about 500 miles but was still throwing the lean code P01071. The hard starting also did not change. Now the random misfire is back, just not as often as before. Again its only occasionally and only at idle. There doesn't seem to be any logic to when it happens - hot engine, cold engine, hot or cold outside, doesn't seem to matter.

Would love some advice on where to look next. I've read some stuff about failing fuel pump but I would think that would show up other times than just at idle? Could one of the new coils be faulty? I've checked for more vacuum leaks by spraying carb cleaner but is there a better way?

Very confused by how intermittent the issue is, and also the fact that the new ignition parts cured it but only for about 500 miles. Current codes are the lean code P0171 and a random misfire code.

 

Side note - if anyone knows a mechanic in the new orleans area I'd be happy to pay someone to look at it, I've just never been able to find a mechanic who will work on these old trucks and actually knows what they're doing beyond suspension work...

 

From your description my initial thought is your injectors are done. As they age the resistances for the coils changes and they just don't work like new anymore. You can take them out and have them tested but they are what, 23, 24 years old.

 

To add to that you can try just unplugging them and checking resistance on them installed but make sure to hit the plugs with a shot of penetrating oil or something first and be gentle or they may break. Look up the resistance spec though.

Otherwise I would spray water around the upper/lower intake manifolds all around to see if a gasket or another hose is leaking. Listen for an idle change when you hose it with water. The fact it's only really at idle suggest to me a vacuum leak because typically at slow engine speeds a vacuum leak has more of an effect than at higher engine speeds