Intermittent check engine light

hi, I am a new member and I have a 1999 4Runner(basic, 4 cylinder) with 249,000 miles.
The check engine light had been intermittently on/off for 6 months, the scanner shows P300 and P301 (no. 1 cylinder misfire),the spark plugs, spark plugs wires, two coils, fuel filter and 4 fuel injectors had been replaced. No. 1 cylinder compression showed 147 psi. After each replacement, the CEL would be off for few hundred miles, then it came back.
Lately the CEL flashes few seconds in the morning (engine cold), then stay on. Scanner shows the same code P300/P301. The car runs great, good power and fast startup, no hesitation and good gas mileage. When engine is cold, it runs rough for the first half mile, when engine is warm/hot, it runs like a champ.
The corner mechanic said he runs out of idea what parts to replace, suggested to take it to dealer.
I took the car to the Toyota dealer, left there over night so they could see/feel the problem, they called and have no clue, then suggested to do cylinder compression check, block check for coolant leak....etc. I told them the CEL flashes when the engine is cold, it may have to do with cold temp sensor or fuel/air mixture during cold start, they want me to leave the car there for another day.

Do any 4Runner owners have this weird CEL problem? or someone may have more knowledge how and what the computer controls the fuel/air when engine is cold, I can pass the info to the Toyota service personnel. Many thanks.

 

Hello,

Yes, I went to Midas yesterday and got similar codes. Mine were P0300, P0302, Po306. The 300 was labeled Random Multiple.

 

Hi, Goosedad! I'm not a mechanic, but my check engine light (and the two VSC lights) is on due to my upper oxygen sensor. I am always learning something new about the inner workings of vehicles, but I do know computers can potentially misdiagnose, or not present complete information, when something is wrong with the connectivity.

I learned a bit about oxygen sensors when my guy plugged in and diagnosed. They have everything to do with the ratio of fuel to oxygen, because it is what tells the computer the ratio in the exhaust so that it can adjust for cleaner exhaust and better fuel efficiency.

As an alternative, maybe you could get a second opinion from another highly reputable, long-standing local mechanic? I personally appreciate having the same car doctor under my hood every time, rather than what seems to me like possibly a different mechanic getting under my hood every visit to the dealer. From experience, my three times at a dealership had a different technician each time.

I'm not familiar with the term corner mechanic, because usually folks around here just say "my guy". If I'm suggesting what you've already done, I apologize. And it was some time ago, I just noticed the date. I hope that you were able to fix the problem, and if you have the time to port your outcome, it would most likely be helpful to others.

=)