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Discussion Starter · #1 ·
Mystery: 2001 Tundra (3.4L 238,999 miles) runs rough at idle for 10 to 20 seconds.
It's had this problem for a while but its getting worse. Here's the behaviour;

1 When I first start it in the morning it usually runs rough for about 10 to 20 seconds. After that it smooths out.
2. The engine light comes on and says that it's missing on random cylinders.
3. It doesn't do it every time. Sometimes it starts up running smooth right away.
4. Sometimes when I'm trying to accelerate when I'm already going above 70mph it cuts out.
5. Yesterday it was really running like crap. I could barely get it up to 65 on the freeway. It was doing a lot of bucking and cutting out. The fuel tank was almost empty.
6. After filling the tank, it ran much better. I had no problems driving in to work on the freeway this morning.

I've taken it to the dealer quite a few times. They;

1 Replaced the spark plugs
2. Found a broken plug that cost $800 to fix.
3. Found and fixed two cracked heads for $4000.


For each one of the changes the problem would seem to go away for a while and then come back. The last time, they cleaned the air flow sensor which seemed to help but only for a few days.

It seems like the fact that it goes away so quickly after starting means that the problem has to be close to the ignition or exhaust system. There's not much that would warm up that fast.

Does this sound like anything? Anyone have any idea what I could check? At this point I'm thinking it might be the fuel pump, regulator or relay. Has anyone else had these symptoms and was able to fix it?
 

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It could very well be the ignition coils. Been there, had that.

Some years ago, I was on a trip and one of the original coil packs failed failed. There was a dealership nearby, and the coil "repaired itself" on the way to it. It had thrown a code, and so there was no doubt what or where the problem was. My analysis was that it failed internally, began sparking internally, and sort of welded the break back together internally.

I returned home (about 600 more miles) and replaced all eight coils with a set of used coils I bought on eBay. Coil packs are not cheap. These were made by PEC (Precision Engine Components) of Australia. They worked, but they were not the quality of the original coils. The engine idle was not smooth, and the lack of smoothness was not constant; it oscillated over about a ten second period. Lately, if felt as if it were trying really hard to miss, particularly at low throttle settings when the there isn't much to ignite in the cylinders, and the cylinders did not all pull evenly. Even the exhaust sound made this obvious.

So, a few days ago I replaced the coils, and now it drives like it did when it was brand new. The idle is smooth and all eight cylinders pull the same. Even the exhaust sounds better. After 195,000 miles, that still amazes me.

The replacement part was a Denso 673-1303, ordered through RockAuto.com for $52.69 each. Denso makes the Toyota OEM part, but it's much more expensive.

If you know someone who has the same engine, you could try using his coils in your engine for a test. That's cheap, and if it works, then you've found the problem.
 

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Discussion Starter · #3 ·
Thanks for the response DJ. Since the code says the misfire is random and it goes away so quickly it's really hard to trace down. I ordered new ignition wires and a coil. I can replace the wires and then swap the coils out one by one to see if that fixes it. Swapping out parts gets expensive though. I wish I could narrow it down but I guess if the dealer hasn't been able to do it...
 
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