My prius runs smoothly when it's cold and most of the time when it's warm. There are times when I pull over and go into a store and it's will run really rough for about 5 minutes of driving. The engine light comes on and gives a random misfire code. I took it into a mechanic and they found fuel in the number 1 and 4 cylinders. I had the injectors cleaned and inspected and the first time that I ran it and then stopped for 10 minutes it started misfiring again. The odd thing is that I can disconnect the spark plug wire on any cylinder and it will run fairly smooth. I'm confused!
P0300 Random misfires normally caused by vacuum leak and bad fuel fuel-
April, 16, 2011 AT 1:23 AM
Would that cause it to misfire when it's warm but not when it's cold?
September, 3, 2011 AT 4:54 PM
I am having the EXACT same issue with my 2002 Prius with 140000 miles. Did you ever find a cause? I had mine in the shop for 3 days and they replaces the o-rings on the fuel injectors because they appeared to be leaking some fuel, but it did not solve the issue. I have cleaned the mass air flow sensor and throdle body. I replaced the plugs last year. The only othe issue with the car is that the A/C only works for a little while and the green light stops flashing and it stops cooling. I assume this is unrelated but thought I would share as much data as possible since this is a tough one to solve.
September, 22, 2011 AT 6:30 AM
As the spark plugs heat up, their resistance increases. That could cause it. It could also be a vacuum leak that doesn't happen until the leaking part heats up and expands. Try running a can of good quality fuel system cleaner through your tank, change the plugs and wires, and check to make sure the coils) is/are functioning properly once heated up.