QuestionI have a 2000 Toyota Tacoma, 4x4 extra cab, 3.4-liter DOHC EFI V6, w/47k miles.
Background info: Never had a problem with the truck, oil changed ~5000 miles or so. I commute with it and take it snowboarding in Tahoe a few times a season.
A few years after purchasing the truck, I heard 'knocking' from the engine bay when accelerating. A friend traveling with me said that I probably need a valve job due to the knocking. This issue went away about a year ago. (Not sure if this is related to the issue)
The car passed a Smog check with no problems in August 06. I changed the Air Filter around the same time.
Problem: In early December the truck started to have a 'rough' idle. It also has very sluggish acceleration in 3-4-5th gear while getting onto the highway. Hmm, maybe I need a tune-up?
Last week - The engine check light came on while driving to work. Hmm, better take it into the shop. Drive home and use other car to work the rest of the week.
My coworker gave me the number to his mechanic which he mentions is really good. I start the truck to take it to the shop, but no engine check light? Still has a rough idle though.
Mechanic hooks up diagnostic equipment and says that cylinders # 2 & 5 are misfiring when the car is at running temp. He noticed that I had a small coolant leak and was running at 1/3rd. He fills it up but still has the same problem. I never noticed because when the car is running, the engine gets cooled off by the airflow...
They spray propane into the intake and he says that all cylinders are running OK.
Resets the ECU - No help
He thinks the Cat(s) converter may be clogged. They disconnect it from the header but the truck still runs w/4 cylinders when heated up. (Broken bolt too, sounded like one of those ricer cars when he took it out of the lot...). He states that its running fine when just started up and cold.
He changes the spark plugs - No help.
He changes the Mass Air Flow Meter - No help
He changed out the coil for those 2 cylinders - No help
He checks the spark plug wires - fine. (Not replaced, but there seems to be no damage / arcing)
Next to his garage is another garage with a former Toyota garage forman. He is also baffled at this issue and has never seen it before.
Grasping for troubleshooting ideas, I also though of: Fuel filter or maybe the Injector is clogged? He is still troubleshooting the truck. He thinks it is another airflow type of sensor that is messing up the ECU input readings.
Thanks in advance for any suggestions, Glenn
AnswerYour friend is wrong. If you needed a valve job, it'd tick insessantly from the top of the head, times however many of your 24 valves need adjusting, never ending.
Most likely the engine is detonating. Clean the EGR valve. (Might aswell clean the throttle plate & idle valve at the same time) Replace the plugs with the specified NGK, or Denso plug. Your plugs may be too hot. Whatever plugs he put in there. Take one out & if it's anything else. Throw it away. It's fucking shit, and will run like as by summer compaired to the OEM advised plugs. (Denso ignitions like Denso plugs. Period...)
Seafoam the engine afew times in the intake, or run water injection to bust the carbon out of the combustion chamber.
He should have never changed the MAF, nor is it a sensor problem of any kind.
Toyota fuel filters almost never need changing. They have no published service interval. If anything about the fuel delivery system itself were defective, you'd be running lean on all cylinders, not 4 of 6.
The injectors are most likely clogged/failed - tho they are fairly uncommon to happen on Toyota's than most other brands.
Fix the coolant leak before you warp one of your heads from overheating one day.
