Just bought my first 4runner last week.
2002 sr5 v6 auto 2wd with 151,000 miles on it

Im having an issue (bought it this way) where my idle will fluctuate slightly up and down only in park or neutral. Its very minor, not even enough to show any difference on the tach. But its enough to hear and feel slightly. Also on the freeway it seems extremely sluggish and very loud to accelerate. Absolutly no passing power and I have to push it harder than I prefer to get if up the mountains (while barely maintaining speed) There is no CEL or anything at all. Just passed smog the other day with it doing this as well.

Heres some info
-151,000 miles.
-The latest owner said that he didnt know if the timing belt was done or not when I asked him (he didnt have it for a year yet). I have the full OEM kit (from ebay aircabinman) with pulleys,water pump and tensioners sitting in my garage waiting for me to put it in. (within a 1.5 months because im going on a 3 week vacation)
-New ngk sparkplug wires and dual ground plugs. (also from aircabinman)- installed last night
-B&M tranny cooler mounted and will be hooked up when I do the timing belt job (got one of the 2 suggested off the buyers guide sticky on this site)
-Just got inside from putting a new fuel filter on (no luck)
-Checked all vacuum lines. Seem leak free, tight, and in good condition
-Cleaned MAF sensor
-Cleaned PCV valve

NO CEL either. It seemed like a misfire to me at first and had high hopes that the plugs and wires would sort it out. But so far no luck. Ive spent the entire week scratching my head, waiting for parts to come in, hoping, and scouring this site to see if anyone has posted this issue Im having. Im not about to bring it into a stealership and have them charge me 150 dollars to get a computer diagnostic and another thousand to fix it. I could buy a scangage for their hook up price (saving for one right now). Im a military aircraft mechanic so I can figure things out with a wrench and a search bar, but troubleshooting this issue is getting the best of me. I dont want to throw money-parts at it without being certain it will help or fix it.
If anyone can help or point me in a good direction. Please let me know.

Also. If I put the air cond on while idling the fluctuations will stop. The truck idles at approx 750 via the tach reading when warm. When you start it at first and the fans are on it does not do it either. But 10-30 seconds later when they kick off it begins

How much does it fluctuate?

You said you cleaned the MAF, but have you changed out the Throttle Postion Sensor?

Wait, you can't change out the TPS on an '02, can you? I think you have to get a new throttle body..... Which =$$$$$$$$$ from the stealership.

Havnt changed the tps yet. Hope its not the throttle body.
The other day I cleaned it out. It wasnt too bad at all but I did get some carbon out. I messed up my idle rpms (now adjusted and fixed) because I removed the screws and investigated inside where the tps plugs in to. At first id start it, rpms would automatically spike. Then it would automatically stop. I dismounted the tps and took off the screws attached to the receptical side on the throttle body. Re-seated it so that the throttle wasnt stuck open and the truck wouldnt peg it upon startup. However the rpms were higher that evening. Idleing at 1900 during start up. And 1700 once warmed up for a min or two. I had to loosen the set screws on the receptical side and adjust the idle to my desired 750-800. So at least I learned how to adjust the idle on a 2002.
However my original problems still exist. Im going to change my timing belt in a month (roughly) so I will wait to see if timing is the issue. I also have a obd bluetooth tongle coming in the mail so I can run the torque app and see if I have any pending codes. I cant wait to get to the bottom of this issue. Ill post findings / fixes as I deal with it and troubleshoot.

http://m.youtube.com/watch?v=Gb__ZeU8GgU

The link (or address above) is a exact replication of the issue my truck is having. I didnt find any responses or information on the video. Searched all over. Even the tacoma forums. No avail. The rpm on the tach doesnt bounce. But you can feel a slight studder once in a while. And you can easily hear it from outside or with window down in a garage. Only happens in park or neutral. No load. And when eng is at the lower idle speed you achieve after it runs for a few minutes at start up. Press the gas and it stops fluctuating. Turn ac on or put it in a motion gear. It stops.

Drove from nor cal to las vegas and back. I noticed that this problem happens when you coast the car and engine has no load on it at all. (AC off and coasting in drive). This tells me that it happens under no load circumstances in all gears. I purchaced a bluetooth obd tongle and the torque pro app. There are no codes at all. Idle rpms are 650-740. Still have this issue and still driving me crazy. The truck also seems to have insufficient power. Driving up gradual upgrades and mountains it struggles to keep up to the speed limits without downshifting twice at speeds over 55mph. Intake is extremely loud too and seems to have no torque. (Struggling to maintain speed limits up those hills and seeing a few 3.4 tacos blaze past me while my engine is screaming)

Also I got a brand new denso oem maf sensor. No change in status at all

Next steps to be completed will be new oem complete timing belt waterpump pulleys and tensioners. Ill check to see if there is no play at the crank and ensure my cams gears arent off a tooth or anything silly like that. If anyone has anything else I could try please chime in. Any help or input would be awsome.

Been a while. I'm in the middle of installing a new timing belt, water pump, pulleys and tensioner. While installing the new timing belt I snapped the bolt that holds in my idler bearing/pulley. Gonna have to drive 40 miles with the wife to buy a new one. (Part Number 90080-10289)
Back to the status of the 4runner. My old water pump has started to seep. There were hardened rock like greasy anti freeze fossils stuffed all throughout my lower timing cover. When I Lined my cams to to top dead ctr, my crank timing mark was off by 3 teeth. Hopefully the new belt\s will give my truck some more highway power. If not, then at least I'll be slowly driving at the speed of "reliable".

PROBLEM SOLVED-- installed the new timing belt kit (the oem one with idler bearing and hydraulic tensioner/bearing) from air cabinman on ebay. Now idles so smooth I cant feel it. On top of that I feel like ive got 50 more horsepower and better performance I thought id get out of my newly acquired 4runner. It took a while because I had to wait on amazon slow-free mail for my special service tools. When the water pump chudded greasy rocks of antifreeze, grease, sand, and nasty stuff it contaminated everything behind the timing cover, the belt picked up the contaminents and skipped 3 teeth on the crank. Thats about 30 degrees of ill timing. The timing job ive done in this truck is the most extensive and in depth ive ever been in any car. Its a good confidence boost to grow sone balls and fix it yourself saving alot of date money to keep the wife happy.