Esto pille por ahi, a ver si te sirve de algo .......
Question: 1997 Toyota 4 runner 3.4 mileage 185k. I noticed that the truck had lost some power, so I did the plugs, wires, air filter and fuel filter, truck is super responsive and revs up clean....definitely a noticeable difference. I also had the timing belt done back at the recommended 90K or whatever it was; not sure off hand but it is about due for another timing belt. Anyway it pulls strong, but seems to have some very minor break down on the top end...perhaps about 4500 rpm or so. It is faint but as I build and race cars (Camaros) I notice it. You can hear the motor rev and it does accelerate but not as strong as it should...almost sounds as if it is bogging a little, but seems to be more of a breaking down (loss of spark) than anything else. I am thinking it is coil related? The truck has three coil packs one fires one plug on one bank as well as the other on the other bank. The truck is completely drivable, does not have any skips or misses, however seems to have some break down as mentioned. Any thoughts are greatly appreciated...I drive the car pretty easy but noticed the problem when goosing it onto the highway. The car does not pull any codes.
Answer: Your type of problem is one of those trial and error queries. The first thing to do is do a compression check. If compression is okay, you may have either a bad coil pack, or mass air-flow sensor or fuel pump. Try a new coil pack first. If this does not cure your problem, move on down to the mass air-flow sensor and finally the fuel pump.
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