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Engine shaking + jumping randomly; CEL code p0302

10-29-2011, 03:03 PM
I have a 2003 Tacoma PreRunner (2.4 L) with about 145,000 miles on it.

About two months ago I started noticing that the truck would shake slightly at times -- primarily when I started it up in the morning, but also sometimes when stopped at a light or stop sign. I also sensed that the engine was jumping/hesitating sometimes when accelerating. These things would happen sometimes, but not others, so I didn't immediately do anything about it.

It slowly got worse over time, to the point that the truck would sometimes shake strongly enough to feel like I was in a blender. Then I drove my truck up the coast (about a 6 hour drive each way) and, the day after returning, things got much worse. When idling the car would shake violently every time, and when accelerating the jumping/hesitating was more noticeable than ever. On my way home from work that day the check engine light came on, so I called my mechanic to come out and have a look.

He ran a test on the check engine light and looked up the CEL code and it read p0302 (cylinder 2 misfire). The next day he went under the hood and took apart much of what was underneath, but he couldn't diagnose the issue for-certain. He suspected the spark plugs so he replaced them. He also replaced the air filters and did a transmission flush and an oil change.

For the next two weeks the truck ran smoothly -- no shaking or jumping. Then I took another road trip up north and, upon my return, the truck has started having the same problems again. No check engine light yet, but again shaking/hesitating AT TIMES.

The thing that is puzzling to me is that the problem is not consistent. Sometimes it shakes on startup, sometimes it doesn't. Sometimes it shakes when idling at a stop light, or when parking, but sometimes it doesn't. Sometimes it hesitates when accelerating, but not always. It will go a couple days without issue, and then the problem will start again. But it does slowly seem to get getting worse, again.

I know the shaking is coming from the engine, because when I pop the hood and run the car in idle, I have seen it shaking furiously. Typically the engine will run smoothly with minimal movement for quite a few minutes, and then suddenly the engine will start vibrating madly before settling down again. The vibrating sometimes lasts only a few seconds, and at other times much longer.

Anyone have any suggestions as to what I should be looking for to diagnose the problem? Is there anything to be learned from the fact that my mechanic's initial actions DID resolve the problem, but only for a two-week period? Any help/advice would be appreciated.

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