Intermittant engine sputtering

[LearysGhost]

1998 4Runner 248K mi.
A while back I had an issue with rough idle after the engine warmed up but it would only idle rough after I stopped and restarted the engine. When I gave it bit of heavy acceleration it would stop the rough idle. This was 20K miles ago. When I repl the plug wires the problem went away.
This time I have the same issue so I repl the plug wires & boots, wire brushed each spark plug, cleaned the intake manifold, and repl the fuel filter. The next day it ran like new all day. On day 2 it went back to rough idle but was intermittent. It would rough idle at a stop light or on the freeway. I don't think it's an injector b/c it's intermittent and comes and goes. At Auto Zone they told me there are 2 codes....300 and 306.
I would hate to keep throwing parts in and not knowing the proper part to repl.
Does anyone know what is the most likely issue? Any advice will be greatly appreciated.

 

[joeflem]

Same exacty problem...

Dude I had the same exact problem. Injector's can be intermittent. Pain in the ass but you can swap the injectors and see if the code switches cylinders. I pulled my injectors and sent them to Witchhunter and they checked out ok including resistance. Put them back in and problem returned. Took it to a local shop I trust and they pulled the injector and showed that the electrical coil was failing and only showed 3 ohms resistance (supposed to be 13 - 16). I'd troubleshoot it by pulling the injectors and putting a meter on them to check the resistance. If they check out ok you can make sure by swappin the #6 and another one of them to see if the code moves around after you put it back together.

This was my saga...

http://www.toyota-4runner.org/3rd-gen-t4rs/138866-rough-idle-check-engine-light.html

 

[LearysGhost]

The next day I purchased a coil pack and 6 NGK plugs from the dealer and took care of the misfire issue. Good to be back to 6 cylinders.

 

[Baja Runner]

Rough idle USUALLY means 2 things;

1) Idle Air Control Valve
2) Vacuum leak

Having many 3.4L motors, a very common issue is the idle air control (IAC) valve sticking over time. It needs to be cleaned. The most common symptom is rough and/or low idle at warm starts.

In order to do this, you'll need to remove the throttle body, and the IAC is attached BELOW the TB (so it pulls off as an assembly). Clean the crap out of the TB (be careful not to drench the Throttle postion sensor), and remove the IAC which is held on by 4 phillips head screws that just love to strip, as they are made from a soft material.

Once the IAC is pulled from the TB, clean the port, you'll see its black from blowby gas. First time you do this might take you a couple hours, but its a very simple procedure. After doing it about 1-2 times a year just as a maintence item, I could do it in probably 30 minutes!