Okay, can't give you guys a code, my truck is conspiring against me to keep me from getting one. It's a '99 2WD with the 3.4, 187,000 miles, lately, did the valve cover gaskets, plugs, coil packs, cleaned the throttle body, and changed the old cracked hose up top that connects to the throttle body.

Off and on for the last few weeks the truck's had an intermittent weird surging feel, loss of power sometimes when driving then it quickly recovers. This only happens after the truck's been driven for a while, usually after twenty or thirty miles.

It's gotten worse. Runs fine when cold, runs fine on short trips, going to work is about a 40 minute trip, invariably, within five minutes of getting to work or getting home, the thing trips the CEL now, idle is very low, it stalled on me once, has the same bad loss of power intermittently. You can put it in neutral at a light, rev it up to 1,000 and it'll idle fine but CEL stays on. Get to work, park it, by lunch time, whatever's wrong has fixed itself - no CEL light comes on, truck runs fine. Truck runs fine getting me back and forth to lunch joint, ten minute round trip.

Going home, same issue, about five or ten minutes from the house, the CEL comes on, low idle, loss of power, etc. Let it sit for half an hour, the CEL will clear itself (honest) and truck will run fine. I'm in South Louisiana, there aren't a whole lot of auto parts stores on my route, and the two I do pass are in mid-route both ways, have had it checked there, but since no light is on, no codes are showing up. Is this a glitchy MAF sensor? It's making me nuts. I'm used to being able to drive this thing anywhere, and I've checked vacuum lines, and done everything else I can think of - problem seems oddly consistent whatever it is. Thanks guys, sorry for sounding dumb on this one.

Codes are stored even if the CEL is off, at least on every OBDII vehicle I've checked. Maybe time to spend the $20 on an adapter so you can check your own codes and do other diagnostics with your phone (Torque if you're on Android, don't know of an IOS option).

Anyway, I have the same as you only not to the same level. Just did the same work (valve covers, plugs, wires, cleaned the MAF/TB and IAC, water pump, timing belt, etc...) and have a weird stumble at idle once warm. No CEL for me, fuel trims are looking normal/within spec. I also replaced all of my vacuum lines with new silicone.... It's an irritation for me at this point, but I can see it getting worse and developing into what you have.

Well each electronic part can be tested via the FSM.

Yet before I'd replace an untested MAF, I'd make sure I cleaned the IAC very well.

Luck and enjoy the Runner.

I had a similar issue with my '99. It would intermittently lose power and bog down then throw a CEL and it was for a TPS issue. Changed the TPS out but the problem was still there. Ended up being the wiring to the TPS. Went to the junkyard and got a new section of that harness and spliced it in. Problem hasnt come back since.
Best bet for you would be to get a cheap bluetooth OBD scanner and check the codes when the CEL is on.

I'll add that I replaced the TPS 2 times. First with an aftermarket one that was crap and made me have other issues and then with a OEM one from the junkyard and it was good.

I agree that it sounds like a TPS issue. If you check the pending codes, I'm willing to bet it's a P0120.

Put in a new TPS about 2,000 miles ago. It went bad, threw a constant code when it died, oddly enough, truck didn't act nearly this weird when it went bad!

I do agree, I need to get my own diagnostic tool, I'm intending to keep this thing forever, I've had it about six years now I think and it's been the best vehicle I've ever owned - only thing that kills me is it has the 4.10 rear axle so gas mileage is awful and at 60 mph you've pretty much reached cruising speed!

I'm one of those guys where things just have to make sense, been playing with cars since I was a teenager in 1978, which is another reason I love this truck, I can still work on it! This goofy little issue is making me nuts though.

I should also mention, on occasion, even after the aforementioned period of sloppy idle and loss of power, without shutting it down and parking it, sometimes it returns to normal operation all by itself, but the CEL does stay on until you turn it off. Turn it off, crank it again, CEL is gone. That's happened several times, including last night when I had to make a stop on the way home. Was running fine, no CEL, parked it to go into Walgreens, came out, cranked it up, it immediately started running goofy, CEL came on, continued on way home, within a few miles, it was running fine again. I shut it off when I got home, cranked it again, CEL light was gone, truck continued running fine.

This morning, did its usual routine, ran great until I was about five minutes from my office (lots of stop and go traffic and sitting at red lights) it started acting up, CEL came on. What the devil is this madness?

Get that code reader... whatever you choose. The code will be stored.

-Charlie

Clean the IAC if you haven’t done it already. Sounds possibly like a small vacuum leak.

But as @phattyduck said, get the code read. Otherwise we are just blindly throwing darts.

Okay, it finally threw the code this morning and kept it - PO120 - again! TPS. I just changed the TPS in the truck about six months ago, it might have 3,000 miles on it. AutoZone Duralast part (I know, don't use that junk), but, since they're the only place anywhere near me, that's all I had first time and the original one flat died when I had to replace it, was a much more obvious problem.

On the plus side, lifetime warranty, so, replacement TPS didn't cost me anything, just hoping it fixes the problem for more than six or eight months this time!

Might be worth it to at least clean the MAF sensor, throttle body, and change air filter if you haven’t done so. Couldn’t hurt to have everything downstream of the TPS clean. Glad your getting closer to the problem ��

i just had a similar but not the exact same issue I just documented I ended up having a bad CAT. first Try to isolate to make sure you don't have a vac leak needle nose pliers to pinch hoses and you can use carb cleaner, brake clean, or even windex to spray on gasket areas and listen for changes in idle. To check if you have a bad cat try to get a steady idle and plug the gauge into manifold vac and read the gauge you can also use the gauge in the front o2 sensor port if you make a plate with a tube and measure back pressure. (look for a Utube video for a DIY) Keep us informed.

If you have any junkyards near by go junking and get a used throttle body. I have two spares so that’s two IAC and two TPS. I do not like any electronics from autozones house brand.

For non O2 sensors it’s BWD brand or Napa or OEM depending on the sensor.


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Drove quite a bit last night and back to work this morning, issue seems resolved with the TPS change. I'll still clean the MAF over the weekend, weather permitting, certainly can't hurt.

I wish I could find spare parts down here! There are a LOT of 3rd Gen 4Runners on the road in south Louisiana, but whenever I find one in a junkyard, they have invariably been stripped to the bones of all usable parts within days of arriving.

that's cool. good to hear. when we test-drove ours just before buying it, it threw a CEL that turned out to be the TPS. it was resolved when they swapped it out. it was driving kinda punky like it had a cold.

I just went threw a surging issue with no cel ended up being bad CATs I spelled it ou F a couple days ago contact me if u need help