2005 Prius, just about to hit 180K miles. Runs rough at idle, especially when first started for the day. Seems to smooth out as the vehicle warms up. DTC codes (pulled with cheap Wi-Fi ODBII module and "Car Scanner" iOS app): P0300, P0301, P0302, P0304, and sometimes P0420. (Doing the "deep" scan gets a few more, but reading up on the forum here makes me think these are not useful). Things I've done over the last few months to try to address: Four new NGK Iridium Laser spark plugs Four new OEM Denso Ignition Coil New air filter and cleaned the MAF sensor Run a tank of ethanol-free unleaded along with fuel injector cleaner The above things have helped it to run smoother and given it more pep, but the rough running at start/idle persists. Other observations that may or may not relate: I'm in Minnesota so I'm now seeing the cold weather drop in MPG, but it seems worse than usual, and it's been a little poorer than usual even when warm. Goes through a little bit of oil (presumably burns as I don't have oil spots in the driveway). Exhaust isn't smelly or blueish, though. O2 Sensor 1 (Bank 1) might be totally dead; I'm getting nothing through the ODBII/app and I'm pretty sure I used to. By nothing I mean no data, not zero volts. Anyone have any thoughts on what I should pursue?
Fun fact: I bought this used from a dealer who got it from an auction. He said he didn't trust the odometer, but it was cheap and I didn't care. Well, I learned here on the forum that I can look up the service record on the Toyota site (by registering at Toyota's "owners" site) and I just learned that rather than the 180K I noted above, this vehicle was at 300K about four and a half years ago... lol! So anyway, I still have the concerns noted in my original post, but I've no reliable idea what the mileage is.
1. Check engine cylinder compression to see if you have worn out cylinders/pistons or valves. 2. If compression is good, check fuel line pressure, spec is 44 to 50 psi at idle speed. 3. Maybe one or more fuel injectors has a problem if you did not find a problem with 1 or 2.
Let's start with what they mean: P0300 = Random misfire (non-metered air, low fuel pressure, wet ignition are the typical causes) P0301 = Cyl #1 Misfire detected > same causes as above + low compression P0302 = Cyl #2 Misfire detected > same causes as above + low compression P0304 = Cyl #4 Misfire detected > same causes as above + low compression P0420 = Catalytic Converter efficiency low (exhaust leak, wrong air-fuel ratio, bad upstream (WB) O2 sensor, worn converter, moderate or worse oil burning over an extended time period) This can also be a FALSE POSITIVE as Toyota & Subaru set this code even when there is no detectable problem at all. Did you replace the coil boots and use a liberal amount of di-electric grease????? No possible way you are getting no voltage from the front (wide-band) O2 sensor and do not have a DTC for that as it is a required emissions monitor. So something else is going on, but since the WB O2 would affect all other codes you have and they wear out, I would replace it just because they are a maintenance item.
