I have talked about this issue before, but now it has changed. It's my father's 2012 v with at the time 120k mi. Shortly after he bought it it had once or twice a rattle and misfire upon start-up with pending codes P0300, P0303, P304. It hasn't done it in about two years. In the last month it has had a violent shake and misfire at cold start three or four times so far. It now has 139k mi. on it. I checked the codes and it gave me pending code P0301 cylinder 1 misfire. When it does the violent shake and misfire when he starts it up, after a little bit when it doesn't stop, he shuts the car off and then turns it back on and it runs fine after that, almost like having to restart your computer when it is unresponsive. I know we have seen on the forums head gasket problems so we are familiar with the worst possible problem. Any advice on what we should do/look for?
A borescope inspection or a leakdown test might give you a quick answer on whether the head gasket is involved.
Agree. You have the classic symptoms of a head gasket leak on a Prius. They are different than most cars. It will start out very slow and infrequent. What you have now is not the "worst possible problem". A bent rod or a hole in the block while in the middle of a freeway during an ice storm approaches the worst. If the car is not an excessive oil burner, a head gasket job might be the extent of the expense.
Take off the intake manifold, clean the whole thing, and in particular check condition of the small EGR passages, one per port. This may be "closing the barn door after the horses have bolted", but it needs doing, and will give you some idea of how advanced the clogging was. Relevant lnfo, links and doc's in first link in my signature. Blown head gasket at 120K should be a black eye for Toyota, but they're apparently teflon-coated...
Before my father bought the car the EGR valve was replaced at Toyota. We are not sure if the system was cleaned at that time or not. It doesn't burn any oil. We replaced the spark plugs about 5k mi. ago and the plugs looked normal. We live in Florida, so when I am referring to cold, it is below 60°F. I don't know about the coolant. We will have to see where the level is. I will let you all know what we find.
we used to call this 'cold start rumble' or some such. it is still a possibility, since shutting down and restarting helps. if that's the case, no big deal, but you must determine if you have a head gasket leak, and if not, get the entire egr circuit cleaned
Any coolant lost? Do hydrocarbon check from the coolant reservoir or pressure test and check each cylinder with boroscope or flashlight. I am afraid you have head gasket problem. But make sure if it is indeed head gasket and fix it asap before coolant kill your catalytic converter.