Ok. This one is killing me. It's gotten to the point that I'm wanting to sell this truck.

So, I've got this intermittent misfire/stumble that I can't seem to chase down. When I start the vehicle, it seems to drop a cylinder until the warm up cycle is over. Then the cylinder comes back. While driving around town, everything seems fine, but once I get over 50mph or so, it will stumble. Sometimes it is worse than other times, and sometimes it doesn't happen at all. Also, sometimes, the engine doesn't miss right after starting.

The 4Runner is a 97 Limited 4WD with TRD Supercharger. There's a little over 275K on it. While troubleshooting, I also replaced the injectors with the URD 6 injector kit and piggyback FC. I've also replaced the plug wires (twice), the coil packs, the plugs, air cleaner, fuel filter, and fuel pump. No vacuum leaks. Cleaned the TPS and MAF sensors. Every now and again the CEL trips and it is always misfire on no. 3. I've swapped plugs, coils, wires. Always stays on no. 3.

I'm thinking it is down to wiring/ground or the ECU.

Has anyone had an issue like this?

 

How do the vital fluids look? Losing oil or coolant, as in a noticeable level, or through the exhaust?

Compression check be something to look into and compare against each other.

Timing off or failing components such as tensioners, sprockets, or belts also another cause for misfires.

Pretty good mileage there.

 

 

Thanks for the replies guys!

Getting the compression checked is a good idea. If for nothing more than peace of mind.

I checked the oil and I was a quart low. No idea where it's going as there are no leaks and the exhaust isn't smoking. I pulled the #3 plug again and it was quite oily. I'm wondering if that could interfere with the plug grounding to the cylinder head.

Injectors, coils, plugs, and wires all replaced. Not sure what you mean by HG...vacuum? No vacuum leaks. Chased all those down, and the ones I did have were old seals in the supercharger.