Hard starting, with occasional stumble and stall while driving?

This sounds like a weak fuel pump, or you have a MAF sensor that needs to be replaced, I would service the throttle body as well.

P0300 Random/multiple misfires
P0171 Too lean on Bank 1

Please go over this guide to help you see what is wrong and how to fix it:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Here is the location of the MAF sensor and a guide on how to clean the throttle body:

https://www.2carpros.com/articles/throttle-actuator-service

Also, be sure to check the air intake tubes for leaks between the MAF and the throttle body, check out the images (below). Let us know how it goes.

I'm pretty sure there are no vacuum leaks .. my new smoke machine blows pretty good , and I didn't see a wisp of smoke anywhere , except eventually out the front intake by the radiator.

If there was an exhaust leak , what kind of readings would I get from the rear O2 sensor ?? I can't remember , but I'm pretty sure I had a steady reading on the rear O2 sensors , and bouncing pretty good between .2 and .9 volts for the pre-cat sensors , which I believe is acting normally.

And as for the MAF , what should my readings be at idle , 1500 and 2500 rpm ?? and I'm not sure if my scanner reads pounds or metric.

I'd like to verify if the MAF is functioning properly , before replacing.

And lastly , any ideas on what I need to check fuel pressure .. seeing there's no Schrader valve on this system , I'm not sure what I need to be able to disconnect the fuel going to the rail , and hook up to my pressure gauge.

Thanks again for any and all help.

Good idea, here are the readings for the MAF sensor:

Idle (-700 RPM) 2 - 5 g/s
1500 RPM 7 - 10 g/s
2500 RPM 12 - 18 g/s

Here is how to take the fuel pressure readings:

Fuel pressure at idling .................... Approximately 350 (3.57, 51) kPa (kg/sq.cm, psi)

Check out the images (below). Let us know how it goes.

Thanks , I'll check those numbers tomorrow.

Sounds good, have a great weekend :)

Okay, so the numbers for the MAF look good, and I cleaned the throttle body when I had the intake off a few weeks back.

Now the O2 sensor readings are way off.

Both downstream sensors are flat at about .01v

B1S1 is staying steady around .45
B2S1 fluctuating between .75 - 1.1


STFT B1 pegged at 25
STFT B2 fluctuates 0 - 25

Varied RPMs from about 700 to almost 3,000.

I'm lost, any help making sense of these numbers would be greatly appreciated.

Here is what I see:

Bank 1: Very lean, computer desperately trying to add fuel (+25%).

So I need to ask if there is an exhaust leak? Can you send a short video of the engine revving so I can see?

Here is a guide that will go over the lean condition:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Please go over this guide and get back to us.

I have not noticed an exhaust leak , but I'll give that a closer examination next time .. would I be looking more for it pre cat or post ??

The engine revs up just fine .. but stumbles heavily at idle , often stalling out when slowing down , also is very difficult to start

The leak would be before the cat, but it sounds like it can be a weak fuel pump.

The special adapter needed to attach to the fuel rail is difficult to find , trying to figure out a way around that with what I have.

If it were the fuel pump, wouldn't it be starved for fuel as the RPM increases?

It seems to run fine as long as you're giving it gas, only stumbles at idle.

I would think it would stumble more as fuel demand increased , but it seems to run strong once you get it past 1000RPM

Yes that is true, most of the time a weak fuel pump will affect the engine power but when the engine comes off of idle it needs a good spray pattern from the injectors. When you say stumble is the engine misfiring, spark plugs?

Please go over this guide as well:

https://www.2carpros.com/articles/engine-hesitates

Please go over this guide and get back to us. Please upload a video in your response of the problem.

Multiple misfires code p0300.

Plugs are new, after replacing, it seems that's where the trouble started.

Found several vacuum leaks and repaired.

Have not checked fuel pressure , or spray pattern on injectors, but have gone through most every other possibility.

I have seen the incorrect spark plug or spark plug gap cause this issue, here are the correct spark plugs that are needed. The reason the wrong spark plugs, or gap can cause this problem is because they can change the resistance of the ignition system which will slow the ignition timing.

NGK Laser Platinum (OE type):
Part Number: PLFR5A-11
Gap: 0.044 inches (1.1 mm)

or

Denso Iridium Long Life: SK16HR11

I would not have any other spark plug installed but these.

Pretty sure they're either NGK or Denso iridium , I always try to use an OE plug.

And always iridium when the intake manifold has to be removed to get to the back three.

Next time I'll pull the front three plugs and have a look.

Okay, this is a big problem, with todays cars they must be the correct spark plugs.

These are the plugs I put in a few hundred miles ago
I removed the three in the front , and two had this burnt ring at the bottom of the porcelain .. what is that telling me ??

Replaced MAF and fuel pump , starts right up and has steady idle , but STFT are still 25 at idle .. numbers get better as RPM increases , and are within spec once around 2500 RPM

Reading live data , I noticed TPS data doesn't seem to be moving as it should , basically stayed between 3 and 6 as I was giving it pedal .. and once it warms up , it was idling down around 560 RPM , which seems low

Have not seen a code come up for the throttle position sensor .. any ideas on the low idle ??

So it looks like the STFT is trying to richen the mixture. Can I ask if the engine has an exhaust leak? The spark plug looks normal. Also, this can be because of a vacuum leak as well. Does the TPS voltage move smoothly throughout the range? If not, I would put a new throttle body on it.

Please go over this guide of rich mixture:

https://www.2carpros.com/articles/why-an-automotive-engine-will-run-rich

Please go over this guide and get back to us.