A couple days ago, my '99 SR5 V6 4Runner w/ 71k miles started running pretty rough. It would start up fine and idle ok but whenever I put the engine up against a load of just a little more than part throttle, it was lacking power and not running very smoothly. This symptom is a classic case of ignition issues with other cars I have worked on and is usually the spark plug wires, plugs or coils going bad.

Well... I went to the parts store to shot gun a few parts: plugs and wires. After picking up the parts and driving home, the Check Engine light finally came on. Without reading the CEL code, I went ahead and replaced the plugs and wires. Problem solved. The plug wire going to cylinder 4 clearly showed signs of arcing through the insulation (see picture) while the other two wires looked fairly decent. The 3 Denso spark plugs (on the driver's side) looked more worn than the 3 NGK spark plugs (on the passenger's side).

The new plugs I installed were NGK BKR5EKB-11, part number 3967 (about $3.50 each) and the new wires were Autolite "Professional Series" part number 97027 (about $50 for the set of 3 wires - ouch!). The plugs look almost identical to the original (passenger side) NGK's that came out of the engine. The electrode of the stock plugs was shaped slightly differently, otherwise the plugs looked very similar.
I could have purchased a set of 6 NGK LFR6C-11 plugs (the factory NGK plug) but the cost was twice as much as the
BKR5EKB-11's and I would have had to wait a few days for them to be shipped in.

Oh... and after I did the repair (and after I confirmed the problem was resolved from a test drive), I cleared the OBD-II code to get the check engine light to go off. I just stopped by a local autoparts store that had the diagnostic reader/resetter and borrowed their device.

Overall, this was a pretty easy problem to diagnose and fix. It's nice for that to happen every once in a while.

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