This truck is 3.4 V6, 4WD TRD, manual. I noticed the problem around 80,000 miles.

It has had regular tune-ups, plugs, plug wires, air filters, air flow sensors cleaned, etc.. Timing belt and everything in there replaced. Its at 274,000 now. Otherwise it runs fine under normal driving. Gas mileage is same as new almost.

The engine basically has flat spots in the RPM curve. When newer, if you punched it at 2000rpms it would pull hard to redline. But now it is weak until 4,000 rpms, then it pulls normal. It pulls better at half throttle than floored.

One coil pack was replaced because of a skip years ago but it didn't fix the above problem.

Anything to else to check? Most mechanics I know don't talk about programming and tuning for performance, they mainly replace parts.

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Change your fuel filter.I bought a used 2002 Tundra with a 145k miles on it three years ago.It ran fine driving around town.Get it on the highway it was a dog.Pulled the fuel filter and it was almost completely plugged.A lot of water and gunk in it.It runs great ever since.My other 2002 Tundra never had any issues,but it had 212k miles on it so I went ahead and changed it too.It wasn't nearly as bad as the other truck.Both had original factory filters.All it takes is some trashy gas to plug up the filter.

Thanks

Does the RPM jump up and down when starting cold? If so, it may be your intake manifold gasket is leaking which throws off the computer.

Nope. It idles well, about 750rpm. Cranks like new.

The exauhst valves on these wear over time. Toyota used very good seats though. The valves always wear, bit the seats are usually fine.

Do a compression test and also check valve clearance with feeler gauges.

If equipped with variable valve timing, make sure it's in good working order. Variable valve timing systems do wear out, no biggie. These "flat spots" sound like a variable valve timing issue.

It's really nothing to pull the heads and take them to a machine shop for fresh valves. Most machine shops have the shim bucket sets for setting valve clearances.

I've owned 3 3.4l powered toyotas. A t-100 (non-vvt), an 04 tacoma double cab, and a 2000 4-runner.

Another good idea is to clean the intake manifold. I've heard of guys pulling it to scrub it down, but most would use seafoam. The old way to do it was to use the vacuum tube to suck seafoam into the intake while it's running, but these days seafoam makes a spray version that you can introduce it right ahead of the throttle body. It's only ~$10 a can, so it's an easy way to clean up the intake rather than pulling it.

Advance put their code reader on it today. It says "lean on Bank 1", same as it did over ten years ago. My mechanics just ignore it.

I plan to change the fuel filter soon anyway.

How old are the O2 sensors? Might be time for new ones. I recommend Denso.

Have you cleaned the throttle body on it and the mass air sensor?

Yes. Twice.

A little late but I had this issue with my 2000 4Runner. It was the throttle body sensor.

Thanks, all info helps.

Trying to remember

3.4L fuel filter in the tank ??

Being a 'Yota guy

This LC now with 348K miles

Runs smooth & strong

I've used........Berryman's B12.......Marvel Mystery Oil...Seafoam...Lucas Fuel

Snake Oil right ?

try some

I use that Lucas fuel additive quite a bit. I really believe it helps with the 10% ethanol gas we use.

Throwing any codes?

Lean- bank one.

That's on the free parts store cheap reader, not the expensive program pro mechanics use.

$31/gallon jug at Walmarks

I received 3 1/2 gals of that stuff when I bought my 73 Mach 1 in 2013. It sits on the shelf and is free to someone in the San Antonio/Hill Country area.

CEL on?

Does it stumble or misfire? I would look at a legit fuel injector service and change out that o2 sensor to clear all the codes. Good idea on the fuel filter just to cover all the bases.