Codes P0300, P0304, P0171

[dgspencer]

CEL came on in Wife's 1999 Sienna, running slightly rough. My basic OBDII reader showed P0300 and P0304, so I swapped coils from 4 and 6 (probably should have had 1 and 4 misfiring if it were the coil). CEL came back on after a day, this time with P0300, P0304 and now P0171.

I had the injectors cleaned 3 1/2 years ago, one was bad so I replaced it. Should I assume that another injector has gone, or where should I start? This vehicle is driven in town every day, 10 miles or less, ODO reads 101K miles.

[wiswind]

P0300 is a undefined misfire......and P0304 is cylinder #4.
Rather than replacing #4 injector, I would try switching it with another cylinder (easier said than done).
Also, how old are the spark plugs?
If they are original, then you are getting to the point that they are due for replacement.
I would read the owner's manual or look on the underhood sticker to get the correct DENSO or NKG # for your year.
They used different plugs between different years, even in the 1998-2003 model years.
It is critical to get the exact plug, either one of the 2 brands will be great.
The plugs are rated for 100K miles to 120K miles.

It is possible that the P0171 is caused by the misfire codes, the ECM (computer) trying to adjust to compensate for the issues of the misfire, so I would concentrate on the misfire code issue at this point.

I have used Berryman's B-12 Chemtool in the metal can as a fuel system cleaner.
It is one of the cheaper choices on the wall of many fuel system cleaners available at many auto part stores.
I know that AutoZone carries it.
That was the ONLY cleaner that was able to clean the injectors in my '96 Ford Windstar up.
I used it maybe 2 or 3 times a year in that vehicle....which that model year seemed to build up deposits on the spray end of the fuel injector....they had some sort of "hat" on them that would fill up with crud.

[dgspencer]

So, I switched the #4 fuel injector to #6, and the codes came back P0300, P0306, P0171. Time and money wise, it is not worth it to me to try and clean it, or send it out for cleaning. I am ordering a rebuilt FI from RBS for $50.

[dgspencer]

Just to close this thread off, I did replace the fuel injector with a reman. and that fixed the problem. CEL has not come back after 5 days of driving, power and performance restored.

Now for the axle half-shaft...