My first post. Howdy.
My 2008 B2300 2.4l is throwing a P0303 code (for a long time, apparently.)
I pulled the manifold and from behind the throttle plate all the way to the valve chamber the inside is covered with a black, gritty soot.
Yikes.
Air is clean up to the throttle plate. At the intake ports the deposits are heavy but stop abruptly near the valve seats. Number three intake port is especially heavy, with lumpy soft carbon deposits in the throat.
Plugs look all about the same, light tan and the injectors all firing and clean, as near as I can tell.

My questions are many, but most perplexing of all, why aren't my plugs fouled?
And most important of all, where is the oil/soot coming from? I am an old mechanic and not really up on EGR theory and purge valves and all that stuff.

There are no other codes; truck usage is light, milage is ~40,000, with lots of 35mph driving in our small town. Idle was getting rough and that's why I checked codes.
Thanks for your time and happy new year... Mike

 

Disconnect the battery. Clean the MAF, throttle, EGR & Manifold. Start it up with A/C off & let it idle until it warms up then go for a drive & see how it goes.

 

Back together, no change. Still rough idle.
I think I have narrowed the problem down to a vacuum leak in the EGR system.
The soot is from the exhaust.
There is a steady whistling noise which has been going on so long I have been ignoring it.

Is replacing the EGR valve the only remedy, or is there something else in the vacuum system to check?

 

I have reoccurring P0303 and P0300 codes on my used '07 CX-7. The Toyota deal mech said he changed plugs and cleaned #3 injector, but the codes keep coming back. I changed the oil/filter and the code were gone for weeks (instead of always). I thought I was on to something, as the oil was very very dirty. Do you think there could be a connection?
(BTW, the codes are back ) Thx

 

Wouldn't surprise me if it did. Some bloody sensor or the other.

But no, not logically, unless the oil had the viscosity of molasses. P0300 codes indicate the failure of one cylinder or another to produce it's share of horsepower. All P0300 codes (P0301, P0302, etc) can be intermittent.

I swapped my #3 plug to cylinder 2 and my #3 injector to cylinder 1. New code showed P0301. Installed a new injector, still showing a P0301.

Next is vacuum checks. Gotta study the OBD reader and try to figure out how to read manifold vacuum and sensor pids and stuff.

Finally, you may want to try a different repair shop, see what they say. These P0300 codes are a real catch-all and a thousand dollar diagnostic system seems to be a troubleshooting requirement.

 

Try a coil only swap and see if the code follows the coil. Any "chatter" noise on cold start up? And yes, dirty oil will cause the V.V.T. to act up and could set the 300 code.