I have been experiencing a few different symptoms with my 4runner. It's a 1999 V6 SR5 auto. It is still driving and has never let me down, but I wouldn't trust it on a long trip at this point.

Symptoms:
- RPMs surge when starting from cold. This happens sometime and varies in severity from mild surging to almost killing the engine. This started a could years ago and, in general, the frequency and severity have increased over time.
- Generally has a harder time starting warm than cold (I.e., turns over for longer before actually starting). Always starts, though.
- Occasionally when I stop (parking, at a red light, etc) the engine stops. It then starts again just fine. This has happens approx once a month.
- Occasionally the gas pedal is totally unresponsive (no power when I press it) but it only lasts a few seconds and I get power back after pumping the gas a bit. This has happened twice in the last year.
- A few weeks ago, when I started the engine was very sputtery and jumpy. I barely had the power to make it up the ramp out of my parkade and the rest of the drive I had much less power than normal. Since then, I haven't experience the sputter, but on at least one other occasion I noticed that I had less than normal power, especially when driving up hills.
- I constantly have CEL with P0171, and I think I once had P0120 (but I can't remember for sure and can't find the photo I took), but the latter has not returned since I cleared it.

I took my 4runner into a mechanic I trust and, after an initial inspection, his suggestion was to wait for things to get worse because determining what causing the issue would take a lot of time.

Since have had these issues I have:
- replaced spark plugs (but not wires)
- Cleaned throttle body
- Cleaned MAF sensor
- Tried to clean IAC, but not sure I did a good job of this.

I'm looking for suggestions for what to try to fix this. Any help is appreciated.

I have new O2 sensors which I plan to install soon. Apart from that, my best guess is fuel pump.