Hi I am new to the forums and hoping someone on here can help me out. I have a 2005 Monte Carlo LS 3.4L with about 150K miles. I initially had an issue where under hard acceleration the car would bog down and not accelerate past 70 to 80MPH. I took it to a mechanic and they replaced the CAT. It worked fine for about 2 weeks. The past two times I have driven the check engine light flashed for a few seconds. I check the codes and got P0300 both times and P0101 once. The temp around here has been in the single digits and both times the car did this while still cold, it seems to perform fine once it warms up. Any suggestions on what and how to check. I cant really afford another mechanic bill.

 

Plugs wires and coils are a good place to start. Could also be frozen or dirty fuel injectors. Put some "dry gas" in the fuel or maybe injector cleaner. Might as well do a tune up with new plugs.

 

The PO100 code suggest a bad MAF...
The way to check to see if in fact its a problem... Uplug the MAF (Mass airflow sensor) and take it for a short drive... If the car runs fine...Then that's your problem... Its not recommended to drive it like that continuously... Buy a MAF (Mass Air Flow sensor) Be sure its an "AC Delco" and don't buy one from Ebay...

A po300 code suggests random misfires on Multiple cylinders...
not just on 1 particular cylinder...
Replacing/cleaning the MAF should also eliminate that PO300 code as well and you should be all set!

1 other thought comes to mind...
You mentioned that at first it does it at startup but once your running down the road it goes away....
That tells me, Theres a distinct possibility you could have or its a sign that your battery is showing a sign of failure..
Which means once your driving down the road...the battery builds up more of a charge and then the problem disappears..which makes sense...
Considering...everything in this car is run by electricity! Low voltage...low performance...
Since its free...go to your local auto parts and have the battery load tested... I think youll be surprised at the results....

Me personally.. I prefer the old school load testing machines..VS these new "Computerized" battery testers...
So you may need to have them test it 3 or 4 times to get an "accurate" test... Maybe they can take it inside and bench test it?

Hope this info helps!
I'm sure someone else may chime in with more ideas...

 

Thanks for the quick replys. I will try to test the MAF when I get home. If it is the MAF any idea why it would only throw the MAF code once instead of both times like the misfire code?

 

That's a tough one to answer...
But, we all know anything electrical is always a tricky thing to figure out.

 

PO300
PO403
PO405
PO446 ✴︎ ⬅︎ ⬅︎ ⬅︎

All these Codes were triggered by a faulty FUEL TANK PRESSURE SENSOR!

Wait for the Low Fuel Warning before attempting to DIY.
Start engine.
Pull FUEL PUMP Relay ... Let Engine stall to relieve pressure in system.
Remove GROUND Wire from Battery.
With car Raised and SAFETY STANDS securely in place.

Support Tank with Jack.

(I made a "Jig" to attach to the Jack. Sawed the square bottom off from Milk Crate. Drilled holes through Hockey Puck. Mounted Puck to center of Milk Crate with Heavy Duty Zip Ties. Affixed carpet to other side of Milk Crate bottom for padding.)

Lower tank enough to access Sensor atop Fuel Pump.
Unfasten Pigtail from Sensor.
Unclip and Remove Sensor ••• Straight-up.
DO NOT BREAK THE END OF SENSOR OFF INSIDE PUMP!!!

If you need a Charcoal Canister do it when you replace Sensor.

Removing Relay to releive Pressure throws a Code which may require a MIL Light reset.