Frustrating 'P' code question

Hello folks!
First of all, thank you for letting me into the TacomaWorld Forum. I have used this forum as a point of reference as a guest and found it helpful as a problem-solving resource many times before since I do a lot of my own work on the truck.
I have a perplexing problem this time and I would like to see if there is any input specific to what is going on with my 2009 Tacoma 2.7, 4WD reg cab truck.
A little background, I purchased the truck brand new from the dealer way back in '09, now with approx. 300k hard working miles later it's time for a new engine. I installed a long block and replaced a bunch of components with the engine including a new cat, o2 sensors, plugs, coils, fuel injectors, secondary air injection pump, clutch, even a new ECM.
Should be good to go I would think but I have a nagging problem that I cannot solve. I keep getting the same codes no matter which ECM unit I use (new or old) with clearing and resetting each time. The codes are P-2237, P-0303, P-0172. I know what all those are, and the P-0303 in particular keeps showing up, (sometimes alone). I have changed or switched the coil, the injector is new with the rebuild along with the mentioned new components above. The truck starts after a reset and runs a little rough as expected, after a few miles the that seems to clear up but the idle at a stop continues to lope slightly with a low RPM around 600-700, (still with no engine light). Then out of nowhere the engine light comes on, loses power, I'm sure due to the 3rd cylinder misfiring and I limp it home, do the checks and the same codes show up!
I think those codes may be somehow connected thru some common thread or problem I may not be seeing, any thoughts on this? If there is already a thread relating to this I apologize, I tried searching for the codes and nothing came up for all three together.

 

My first question would be where did the parts come from? If Amazon/ebay/china they are probably junk.

The P2237 (A/F Sensor Pumping Current Circuit / Open Bank 1 Sensor 1) suggests either you have an open circuit on the AFR sensor or a failed/incorrect sensor installed.

The P0172 (Bank 1 Too Rich) suggests your over fueling which typically would mean either too much fuel from one or more injectors, an over-reporting MAF sensor, or engine mechanical issue but being the P2237 is present that needs to be addressed first.

The P0303 (Cylinder 3 misfire) could be a cause or effect of the rich condition but again I would address the P2237 code first so it's able to properly measure air/fuel ratio.

 

I would test for resistance with all grounds at chassis and engine points and then continuity at sensor circuits.

More often than not, especially with the aging electrical components, oxidation eventually takes its toll. Most if not all of the sensors are ground dependent.

I also utilize deoxit spray and noalox alongside wire brushing threads and sanding connection areas to ensure I have a reliable and clean connection.

 

Thanks for the replies, both bring up good points to start from.
When I started the engine for the first time after installation some of the same codes popped up and I thought they might have had something to do with the o2 sensors. Those I didn't initially replace until some of these problem codes started showing up. The ones I bought are actually Denso sensers from Napa, so they should be legit. I will definitely do some checking now that you've sent some detailed instructions and parameters for checking that. I am guilty of buying stuff on-line from various resources, I tried to keep them name brand when possible. I'll keep plugging away at some of the low hanging fruit, see what shows up, and the ground connections sound like they might be a good place to start as well. Tomorrow is another day, hopefully I can get this resolved soon. If not it may be time to visit a local shop and have them do a full work up. Ugh...

 

Welcome to Tacomaworld

 

Where did you get the new ecu?

 

I found one at FlagshipOne (www.fs1inc.com) online. Its 'reconditioned' and frankly it showed up looking extremely sunbaked. It seemed to work though, the guy I rebuilt the truck with has used them before with some luck. I figure at least they have some sort of return policy, not a full refund but something if it doesn't work for me.