I have had my 99 limited v6 4runner for about 3 years. It had run beautifully up until recently when the idle became rough and the check engine light came on. I took the car to a local shop where the mechanic replaced the ignition coil for the #2 and #5 cylinders. That stopped the rough idle for about a day, then the check engine light came back on. I was then told by my mechanic that I needed to replace the plugs, so I did it myself, since he was going to charge me $175 to do the job. The check engine light still came back on, so I took it back to him. He ran some tests and to make a long story short, the check engine light still comes on when traveling about 65 miles per hour, but not until then. He doesn't know what the problem is and recommends that I take it to the dealer so that they can run tests on it. I hate to take it there because I fear that I will have to pay a ridiculous amount to get it fixed. Has anyone had this problem before? I will include the mechanic's writeup below. Any help will be greatly appreciated.

Mechanic Writeup: "Engine scope analysis and computer code scan for check engine light: Code p0302, p0305, and p0300 all back in system. Initially suspected faulty plug wires based on inaccurate testing and replaced with no cure. put original wires back on vehicle, tried moving coils around, cleaned off spark plugs none of which corrected symptom. fuel trim readings indicate in freeze frame data that long term trim the computer is trying to richen system but short term trim when code sets is trying to lean out mixture. also noticed long cranking when engine is warm that could be related. fuel pressure within specs and compression readings good compared to non offending cylinders. Based on fuel trim issue, tried factory mass air flow sensor replacement also with no cure. All of this testing with no cure leading us back to original vacuum gauge flutter indicating now burnt exhaust valve or valves. Repair would entail valve job so highly recommend second opinion at dealer."

So everything is working properly, except your check engine light keeps going on?
Go to Autozone and have them run a diagnostic on it (free), it probably just needs to be reset.
I had the same problem, the diagnostic showed I had a bad o2 sensor, but I had him reset it and the light hasn't come back on since.

Hope you get it figured out!

actually, the engine is still missing and running rough, fuel and the check engine light is flashing at high speed. I would have thought that an 02 sensor was the problem, but the mechanic doesn't think so. I have had the codes reset several times by the mechanic, but they keep coming back.

Damn, well it sounds to me like you're gonna have to take it to some Toyota shop and have them check it out, thats kinda weird your mechanic hasn't been able to figure out why is still riding rough.
What do you mean by "missing"?

the codes that keeps popping into the computer "P0300, P0301, P0305" mean that the spark plug and fuel that are being injected aren't being ignited at the optimal time, causing a lack of power.

Then is sounds like you need to have your fuel injection looked at.

http://www.toyota-4runner.org/showth...threadid=30291

me too, i get the light after traveling above 80mph for a while

have you had the mass air flow (MAF) sensor cleaned? i have read where that could be the culprit to rough-idling engines. just a thought

The mechanic did check the MAF, even replaced it with a new one with no result. I am a little weary to take this thing to the dealer, but after reading up on other boards, it seems like this is a problem that may require me to do so. Especially if a valve job is in order. Thanks for the replies to the question, I'll give an update after i have the dealership look at the situation.

I am going to replace the other 2 coils here this week.

my check engine light has been coming on at high speeds for about 2 years now. the two known problems with mine though are o2 sensor (truck runs lean causing the light to go on) it also runs rough while idle and occasionally putters to a quick death, which seems to probably some kind of vacuum leak.

hope this helps

Did you read this part?
Normally a fluttering vacuum gauge would indicate weak valve springs or worn valve guides. Are you comsuming oil at all?

I suggest you take your truck to an engine/valvetrain-oriented shop. The dealership will no doubt have a good engine guy, and probably a Toyota-veteran engine guy at that. But that's not your only option. If you're wary of high dealership dollars, find a good indy mechanic that does engines.

Did you disconnect the battery? Sometime the computer needs reset after replacing spark plugs and what not.

Try a simple injector flush lean mixture not enough air or not enough fuel. Injector not capable of delivering the needed amount @ high speeds just a thought.

Have ur mechanic run an injector balance test