Hello Scotty, I have a 2003 Toyota Corolla with 226,000 miles auto tranny, when I have my foot on the brake while in gear when the engine is cold first thing in the morning, the engine feels like it's misfiring, and bogs down. After a few minutes, when the engine is warm, it runs just fine. The check engine light also came on recently, last time I looked it had P0172 System too lean Bank 1. I've tried replacing the MAF sensor, and spark plugs, but to no avail. What could be wrong?
Could be an intake manifold gasket leak or a faulty Engine Coolant Temperature sensor.
Hook up your scanner and look at the Freeze Frame data to see when that P0172 code is being set. Is it happening before the engine reaches operating temperature?
Then switch to LIve Data ((Datastream)) and watch the fuel trims during warm up. Are they high positive and then start decreasing after the engine reaches operating temperature? (intake manifold gasket leak)
Look at both the ECT and the IAT sensor data. Make sure they look right
Thanks for the reply, I will have to take a look. Unfortunately, I do not have a scan tool, I used one of the ones you borrow from O'Reilly's. I'm not sure what you mean by if it's happening before the engine reaches operating temperature, but if so, the feeling of the misfiring is occurring before the engine is at operating temperature.
If I were you, I would order a brand new OEM denso maf from amazon or rock auto. They cost $45, looks like you use DENSO 1976030
Not sure if you changed it yourself, but it is super easy, takes about 2 minutes, maybe. Try and return your maf you bought from napa and tell them it didn't help the issue.
I would get some oem Denso plugs, unless napa sold you denso or NGK? Total cost should be about $20, part# Denso 4503
Napa is fine to shop for certain things, but most cars, Toyota in particular, is picky about things like MAF sensors, O2 sensors, and spark plugs. Thankfully the price is cheap on them, but they work better.
I don't suggest seafoam, and neither does Scotty, it was made for two cycle engines. Just get some royal purple max clean fuel injector cleaner to start with.
I would get that maf sensor changed first, clear the code and see how it runs. Couldn't hurt to put the fuel injector cleaner in and let it do it's thing.
The throttle body is pretty easy to do, there are plenty of youtube videos, including Scotty's. Here is one showing the maf cleaning as well.
https://www.youtube.com/watch?v=NWCKvU2FmDc
I'm not sure what you mean by if it's happening before the engine reaches operating temperature
He's suggesting you look at the engine's fuel trims AS the engine is warming up. (Not when it's already at normal operating temps... Which is called "closed loop", which is when one typically inspects this data.
What brand of MAF sensor did you use? Might as well ask about what spark plugs you used?
How old is your engine air filter?
Have you tried running some good fuel injector cleaner in it?
I would clean my throttle body for fun, and idle air control while I was at it.
The MAF sensor was from Napa Auto Parts in Nampa, ID. They told me it was professionally remanufactured. The engine air filter was in good condition according to the people when I got my oil changed recently.
I ran SeaFoam motor treatment through my fuel injectors by putting it in the fuel tank as instructed on the container, but it did not help.
I'm not sure how to clean the throttle body, but I'm sure Scotty has a video on it.
As for the spark plugs, I can't remember the brand, but they were from Napa Auto Parts in Caldwell, ID (different Napa), they cost me about $100 for four.