Hi, I have a 2000 Limited 4wd automatic 3.4

I bought it a few weeks ago and it had a P0171 code lean fuel. I replaced the MAF and the O2 sensors and it cleared... but then a new issue.

I have been having intermittent issues where the runner won't accelerate. This happens in two different scenarios;

- I have driven, parked and then if I get back in after a few minutes I can give it gas and have to pump it several times to get it to engage. (most recently I dropped it into 2nd gear and then back into drive and it engaged that way.)

- I'm on the highway, and over 55 mph and giving it gas does nothing initially but then it surges (as I am now pressing down on the gas trying to get it to do)

I've read several things, some say it's the TPS, others say the fuel pump. It's certainly not the MAF or O2sensors cause those are OEM brand new.

I'm at a loss. I already bought a new fuel pump and filter, and I'm getting ready to buy a TPS. I'm praying not the Tranny or crankshaft. My buddy said it could be the differential.

Also I pulled out one spark plug and it looked like new. Getting ready to do a tran flush as well. I've worked on the last couple cars I've owned but I'm still pretty uneducated, I wouldn't call myself a mechanic... More like seeing if I can handle certain things on my own to save money.

Has anyone run into this?

My issue seems very similar to this;
Random hesitation when accelerating

and this...
Loss of power when accelerating

Though your problem might be different, I recently had a stalling issue where replacing MAF sensor and upstream O2 sensor didn't clear various trouble codes or fix stalling (lean running, O2 sensor, MAF sensor, TPS). The bolt for the diagnostic port ground was loose and VERY HOT from arcing. Tightening it fixed the stalling and trouble codes. Might be something free worth checking out

Additional Info, Vehicle has 157K on it.

Things i've done so far;

-Oil change/filter
-MAF replacement
-O2 sensor replacement
-Air Filter Replacement

Possible solutions/problems havent tried yet.

-Changing the Spark Plugs
-Changing the TPS
-Changing the Fuel pump and filter (already bought)
-Another thread mentioned the IAC Idle Air Control Valve?

I should also mention the other 2 issues I'm having although I believe they are completely unrelated.

-The Fuel gauge can read empty when it's full and at span all over the place.
- Between 55mph and 65mph there is a Vibration coming from the front right side of the vehicle.

Does the engine stall when in neutral, park, or when no throttle is applied? Or does it only happen when in gear and applying throttle? What RPM does it idle at?

As for the fuel gauge that is a common problem (does it on mine but doesn’t bother me enough to fix it), there’s even a couple TSBs on it for the ‘00 model year: 47625 and 47627. Here’s a link for a full list of TSBs.
Toyota 4Runner Problems and Common Complaints | Toyota Parts Center Blog

Vibration might be from poorly balanced tires. Though I’d wait for other, more experienced forum users to give their advice before spending money.

So you replaced spark plugs but not the wires? I'd do those next, One at a time to avoid mixing them up.

I see your list has fuel pump, it that already replaced or still planning to do that? That's my next suspicion based on your symptoms. Another suspect item based on symptoms are the fuel injectors, one or more may be dirty and/or not putting out enough fuel under certain circumstances. There are FSM tests for all this, just go one at a time to eliminate suspect items.

Luck and enjoy the Runner.

Thanks for responding! No it does not stall out when idle (at least it hasn't happened yet). After driving it 30 - 40 minutes it idled at about 800-900 RPMs THEN after a couple minutes of running idle (it had been off for about 15 minutes) RPMs dropped down to 500, YIKES.

I also noticed driving while applying steady gas the RPMs would occasionally take a slight drop before building back up again, almost as if it were shifting gears with no more or less gas being applied.

Check for intake tube cracks

I have a 2000 SR5 and Im having a similar issue I think. The runner had 192K on it and never had a timing belt changed. I decided to replace that along with water pump, thermostat ect. I got everything back together and now there is a hesitation when I push the gas. Only lasts a second and then I've got power again. It hasn't stalled out on me yet. I was thinking that I may have one of the cams off by a tooth so I tore it down and checked. While I was in there again I replaced the camshaft sensor not knowing if that may have anything to do with it. Put all back together again. I've also changed spark plugs and wires now. I still have the same issue. The really frustrating thing is that I did not have this problem before I replaced the timing belt.

Anyone have any suggestions as to what to look for next?

Did you reset the ECM? Pull the EFI relay for 20-30 minutes