2004 Prius Misfiring & Running Very Rough

First guess would be one (usually only one) of the coil packs ontop of the spark plugs have given out.

 

You just topped off the coolant reservoir correct? You should check the actual radiator when the car is cool. See if that's low.

 

Both of these are possible signs of a head gasket failure when coolant leaks into the combustion chamber. Electrical misfires typically throw a code/CEL.

 

The o-rings that are part of the valve cover gasket set look to be blown on those two cylinders so all will need to replaced as a set along with the larger valve cover gasket.

I'd try cleaning the COP's exterior by wiping down with a good degreaser and the interior of the COP's with some electrical contact cleaner, let air dry. While the old plugs are still in, clean the spark plug holes with degreaser, wiped out as best as possible, and spray with compressed air very well. Then replace with new plugs and cross your fingers that solves the rough running and keep a close eye on the coolant level. If it keeps going down......

GOOD LUCK!

 

Any time you have a spark plug out inspect the plug and the coil for carbon tracking.

Part 3 -Carbon Tracks are a Common Cause of Ignition Misfires

Once the carbon track starts the coil must be replaced. Basically it's a high voltage leak and just cleaning it will not stop it.

 

Any time you have a spark plug out inspect the plug and the coil for carbon tracking.

Part 3 -Carbon Tracks are a Common Cause of Ignition Misfires

Once the carbon track starts the coil must be replaced. Basically it's a high voltage leak and just cleaning it will not stop it.

 

Start with this

1. New plugs since they're cheap (you can skip this for now if you check them and they're still good)
2. 2 coils
3. Valve cover gasket

And if you can hope for a cool day in Vegas to do this repair

 

1. NGK or Denso original equipment iridium plugs
4. PCV valve

 

Very good idea Pat on the PCV.

He's inferring that a poorly performing PCV valve can allow build up of internal engine pressure which can cause the oil seals to fail. Always a good maintenance item to check. I will now be checking both the older Prius and Suzuki this holiday week(end).

 

Hope it goes good for you.

 

Get a flashlight and look at the front of the engine where the fan belt is and look for red dried flecks which means the engine water pump is leaking and bad.
Did you check the coolant level by taking the black plastic cover off the rad and open the cap to the rad itself and not the overflow tank.

Have you ever overheated the car enough that either the check engine light came on or the red triangle came on the dash?

 

I never liked using just the coolant recovery tank for checking coolant levels.

 

The g2 is bazare the rad can be half empty and the white recovery bottle is full.
Owned my car for 11 years the recovery bottle level has never moved. I can imagine how many
Owners have been burned by this.

I leave the hold down screws off the black plastic rad cover the hood keeps it on so it’s quick to take it off and check the rad and clean the condenser. I watch the oil and ice coolant pretty closely as I’m approaching 120000 miles so sooner or later going to need an ice pump.

Very happy to report since moving to Redline 5-30 oilwhich at operating temp has the same viscosity as 40 weight has fixed my slight oil loss between 5k changes.

 

Wow worst looking set of plugs I have ever seen on this forum. Original plugs.