Symptoms below:

If i go heavy on the throttle (in park, neutral, or in gear) it feels like it’s choking. Like a stutter, but its not always around the shifting so not confident it’s trans/torque converter related. Always happens right around 2800-3000 rpm.

If I jump in and turn the key right away it’ll crank, start up, and die almost immediately. But if I flip the key to on and wait like 10 seconds before cranking, it starts up and stays running. It also randomly stalls while I’m driving, but I just toss it in neutral and it starts right back up.

Cleaned the MAF, TB, and checked all the fuses to make sure they are in there nice and tight. Checked connections on fuel pump and battery terminals. Thinking maybe a crankshaft position sensor or fuel pump but I’m kinda lost at this point. Don’t want to keep throwing money at non-issues.

I’ve also got a P0430 code to go along with VSC & TracOff lights. Just replaced both downstream O2 sensors and the issue persists. Seems like it all started after a pretty hard bump on some rocks, so kinda thinking it may be electrical.

This seems like the sort of fault where even codes aren't much help, and could end up sending you round in circles. You need live data readings and someone who can interpret them. Sorry I know my reply is as much use as tits on a fish

I’m a fair beginner when it comes to working on engines but after buying my used 04 4runner it started hard misfiring and throwing codes. Due to bad spark plugs it was an easy fix. After a few months it started stuttering at highway speeds around 3000 rpm. I thought this was due to a fuel pump, clogged fuel lines, fuel rail, or fuel filter. One day the check engine light was blinking during the stuttering then quickly turned back off. I was still able to pull the code and it had a misfire in cyl 4. I swapped the ignition coil with another cylinder and the code followed the cyl so luckily I was able to track it down to one failed ignition coil. Bought a new one replaced and code hasn’t come back. I also had the same p0430 code and replaced the downstream o2 sensor. Code hasn’t come back.

Your issue sounds like a fuel or spark related issue. Sounds a little similar to the problems I had.


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I think I’ve narrowed it down to the plugs/coils or the TB (based on some info from another thread). I’ll probably end up doing both at this rate, but I’ve sure new plugs wouldn’t hurt now that I’m closing on 200k

You have mentioned 3 possible causes for the issue you have, I would recommend doing them all with the mileage you have BUT do each item one at a time and then test drive your T4R which will tell you for sure what part is causing the issue, please post your results on the forum to help others with a similar issue in the future!

Replaced all 8 spark plugs (coils were fine so I kept those) but the issue persists

Going to do some more digging and see if I can come up with a possible solution before I start replacing everything. Still won’t go above 3k rpm, regardless of gear. Does it in P, N, D, doesn’t seem to matter

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Since you seem mechanically inclined, I would just verify your timing at this point to rule it out. All you need to do is pull the two plastic cam covers and set the engine to TDC, the cams should line up with the line marks on the casting (the T is for timing belt service position, you can use that if you want, but then you want to use the dot after TDC on the lower cover.)

I would also verify fuel pressure if you can and maybe carefully spray some carb cleaner around the air intake boot and air hoses to check for any oddball air leaks.

That'd be some quick and easy checks I would do after cleaning the MAF, TB, and checking the plugs.

Could be partial plugged cats.. easy to check with a thermometer check temp before and after the cat there shouldn't be a noticeable temperature difference between them. If the down stream side is considerable cooler you found the problem.

I checked the temps pre and post-cat. Registers about 500-550 pre-cat, and only ~320 post-cat so it sounds like a clogged cat may be my issue after all.

Was a clogged cat the issue? I’m having the same symptoms with a P0420 (for 6+ months) and P0101 and P0102 (MAF) codes since it started cutting power at 2800 rpm this weekend.

P0420 - If you've already swapped in a new O2 sensor and the code continues to come back, replace the exhaust gaskets right after the primary cats on the exhaust manifolds. A leak there is going to throw off the O2 sensor readings, even with a new one. Also, only use Denso O2 sensors as they are OEM and others are just not as reliable.

P0101/P0102 - Start with replacing the air filter and cleaning the MAF. Be sure to only use MAF specific cleaner. Also inspect the MAF plug terminals for any corrosion, on both the plug side and MAF side. Worst case, the MAF is failing and needs replaced.

Swapped o2s from a friends rig and that didn’t do it. I have new ones to go with the new exhaust manifold and cat for DS (~$490 from Toyota for the cat and gasket, O2s are denso from RokAuto), just haven’t had time to install it. Had been running fine for months with the p0420 until last weekend. I had a rich condition last year that cut power and shot blue flame from the exhaust. Never threw a code. One key cycle and it was fixed and never repeated itself. P0420 showed up a few weeks after that. I replaced injectors, MAF, ECT sensor, pcv, and vapor purge solenoid (all OEM). I cleaned the MAF yesterday and that didn’t help. Terminals look perfect (less than 10k miles on this MAF). Even ran it without the MAF connected and the power cuts right at 2800 rpm. Air filter is new. 255k miles on the 4Runner. Gonna check cat temps when I get home. Really hoping it’s not the fuel pump (only 30k miles on it) or an electrical issue.

Might also clean the throttle body if you haven't done so recently.

Cats generally don't just fail randomly, there's usually something that causes them to fail, such as excess oil burning and generally poor maintenance. I doubt that is your problem as you seem to try and take good care of the motor.

I had some of these symptoms:

• Truck would have no power randomly (max out around 3k RPM) until shut off for a while then restarted.
• Die (seemingly randomly) while going slowly, and fire up again when I flipped to N while still rolling and hit the starter. Died on me 20 times in a row trying to get out of a parking lot.
• Crank, start momentarily, then die. Then start and run fine.

I'm sure there was other things, but those are the ones I can think of.

Replaced the throttle body with a Tundra throttle body from a scrap yard. All problems went away. Cost $120CAD

Your mileage may vary, literally. Others have had similair issues and replaced most of the emissions and sensor systems, spark plugs, coils, etc. THEN done the TB and that fixed it. I'd suggest to get a used throttle body and just start with that, as it is pretty cheap and easy to acquire, and easy enough to replace.

I swapped in my old throttle body (still worked) and that didn't help. I did find some melted wires to the Bank 2 upstream O2 sensor, tucked up between the engine and firewall. After hours of loosening up the harness and disconnecting things, I cut the melted section out and repaired the wires. It ran fine for a few hours, then popped the 10amp EFI fuse. Now the fuses pop right away at startup. Both O2 sensors look like they were repaired previously and it was a crappy job. I'm going to have to pull the harness into the engine bay and start continuity testing all of the O2 sensor wires. What a pain in the ass.