I have a 2001 XC v70 that recently started shaking badly during idle and when accelerating. After a few days of this the CEL came on. I went to the the parts store and had the codes read, and was given an 0305 cylinder five misfire code. Afterward, I went to my mechanic to talk to him about the problem and he suggested we check the plugs despite their having been recently changed. So we pulled out the #5 plug and the first thing he noticed was how "white" the plug was. There was a bit of an ash color on the very tip, and he said this color should be found further down as well, and that this is an indicator of a problem with the fuel injector not supplying enough gas. We replaced the plug anyways just to be sure.

He suggested that we run a fuel injector cleaner (seafoam or Techron) through the system and see if it works its way out before doing anything else.
I am a bit weary of driving with the CEL on, especially as it will momentarily start blinking if I give it a lot of gas, then return to a solid light when I let off. There have been a few times when it will start running smoothly, but it doesn't last long. Does this seem like a bad idea? Does the fuel injector theory seem plausible?

Thanks in advance to anyone who has thoughts. I have been reading the forum for a while trying to learn about my car, but this is my first post.

 

I had a similar problem that was a mystery for a while... the cause was a cracked stem in one of the coils... I could visually see it. This crack caused intermittent idle flutters and misfire codes. Assuming you have a rough idle follow this process to check which cylinder...
Note: you will need to reset your OBDII codes after this process.
1 Unplug one of your fuel injectors at the fuel log and note the major change in the idle.
2 Plug it back in and repeat for the other cylinders.
3 The cylinder that has the least idle change gets all the attention now
4 Reset the codes
Once you found the cylinder, pull and check for
1 Cracks in the coil housing
2 Moisture in the spark plug hole
3 Pull the plug and check the electrode for debris and ceramic for cracks.
4 If all looks good check the coil's resistance compared to the other ones with a volt meter/ohms meter
5 If all looks good still focus on the fuel injector having an intermittent glitch/ or corrosion on it's plug. It is a good idea to clean the injectors every few years.

Good Luck! Russ