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Po171, Po300 Help ?

bubba9459

By bubba9459
in Ask A GM Technician

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bubba9459 Enthusiast

bubba9459

Posted
Posted

Hello, looking for some help / advice for my 03 Silverado

 

About a month ago, my 03 started getting a rough idle when sitting at a stop light,( SES on)

 

Took it to a GM dealer, they checked the codes, It had PO131, PO171, PO174, PO300, P1133, They said I needed intake gaskets, and Bank1Sensor1 O2 sensor.

 

I replaced the intake gaskets with a FelPro set, Replaced the Bank1 Sensor1 O2, Cleaned MAF, changed fuel filter.

 

Still no good, I am still getting PO171, PO300, and now the P1133 came back. I have cleared codes several times, The PO171 pending comes back within seconds, and after a few minutes the PO300.

 

Still running rough, Leaves black soot under the tailpipes, fuel mileage dropping .

 

I have tried looking for bad vacum hoses, they all seem ok, Tried spraying carb cleaner around new intake gaskets, Throttle body o-ring, Intake pipes,and all vacuum hoses, Nothing.

 

Fuel pressure is 54 with Key on

48-49 at Idle

48-49 at 3000 rpm

58 If I snap the throttle hard.

 

Codes from cheapy code reader :

 

PO171, PO300, P1133

PO171 pd, PO300 pd

 

Monitors 3 inc. Catlyst, Evap, O2 sensor

 

4 Ready. Misfire, Fuel, Comp, O2 HTR

 

Got a vacuum gauge today.

 

Connected to the PCV port I am getting a steady 17 in, with only a Vary, vary slight fluctuation, maybe 1/2 in, or so.

 

With the gauge connected to the PCV port, engine runs smooth, at a normal idle. When I reconnect the PCV valve the rough idle returns.

 

Any ideas would be appreciated

 

Thanks

bubba9459 Enthusiast

bubba9459

Posted
  • Author
Posted

Still trying to find a shop to run the smoke test. No luck, I have called five gm dealers, and none of them do it. Also called 2 of the little specialty shops, they don't have it either.

bubba9459 Enthusiast

bubba9459

Posted
  • Author
Posted

I did put a new PCV valve, and hose on, Nothing. But I guess theres not much chance of the PCV valve being bad since it's just an orifice, no check valve like the old ones.

bubba9459 Enthusiast

bubba9459

Posted
  • Author
Posted

Had to drive it this morning, SES light kept flashing every few minutes.

 

Replaced plugs, and wires today, Bank 1 plugs clean, Bank 2 plugs Black. Cleared codes, let it idle for a for about 10 minutes, No black soot

 

Took it for about a 20 mile drive, ran perfect, Smooth idle, No SES light. Got back home, and let it idle for a few minutes, Went back to rough idle, PO171, PO300, PO131, P1133 back again, Black soot back again.

 

I'm at a loss, I guess, I have no choice now, but to take it to a dealer, and get the royal treatment.

blueyedevil911 Enthusiast

blueyedevil911

Posted
Posted

I will say I just had this exact thing happen to me, but with the Bank 2 Sensor 1, but exactly the same symptoms. Replacing the sensor fixed me. Could you possibily have got a bad new sensor. All your codes still point to a bad sensor. I had seen a video on Advance Autos web site on how to test a sensor to see if it is working properly. I would give that a shot before going to the dealer.

bubba9459 Enthusiast

bubba9459

Posted
  • Author
Posted

Took it to another dealer, They suggested replacing the other pre-converter sensor, Bank2 Sensor1, even though it didn't have a code for it.

 

So far, Seems to have fixed it, Haven't had any more trouble.

 

Doesn't make much sense, but I guess if it's working

  • 3 years later...
farago2r New Member

farago2r

Posted
Posted

I also had the same symptoms. Engine misfiring, running rough, black soot coming out of tail pipe and engine codes p0171 and p0300. I replaced the Bank 2 sensor 1 O2 sensor and the problem was resolved. Truck running great again.

 

Thanks for the advice!

sahls01gmc Senior Enthusiast

sahls01gmc

Posted
Posted

That is about the identical problem I am having! Can anyone verify some Part #'s from Rockauto? I think I will just replace both upstream sensors while I'm at it.

 

How many miles are on you truck?

  • 3 weeks later...

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