Engine Surge

[PrairieGM]

1999 5.3L V8

I've been battling a idle engine surge through the winter. It'll surge a couple hundred RPM, between 500 to 900. Runs rough, but usually doesn't stall, it only stalled on me once in a parking lot. If I hold the pedal to maintain an idle it'll run smooth. Only occurs in the winter, eg. 10F or colder, usually on startup but can occur afterwards. Once it warms up it smooth out and the surge goes away. Tough to determine because it's intermittent, even on similar days in the winter it may or may not occur. Never have had the problem occur in the summer. 

Replaced MAF, fuel filter, air filter, PCV. Checked the air intake, have not detected vacuum leaks (not smoke tested though). Codes P0171/P0174, I scanned it and pulled up the freeze frame data from the latest code setting, which if I remember set a couple of weeks ago: 

 

LOAD: 3.5%

Coolant Temp: 63C 

Short Term Fuel Trim Bank 1: 35.2%

Long Term Fuel Trim Bank 1: 24.2%

Short Term Bank 2: 32.8%

Long Term Bank 2: 24.2%

Intake Manifold Absolute Pressure: 34.0kPa

RPM: 908

Vehicle Speed: 20km/h

Air Flow Rate from MAF: 9.39g/s

Throttle Position: 5.9%

 

Not sure what it could be, Idle Air Sensor or intake gaskets? Any help would be appreciated, thanks!

[Brianibew]

Try replacing the fuel pressure regulator.  Very quick and cheap fix.

[PrairieGM]

Is there a way to check the regulator? I've checked the fuel pressure before, it checked between 55-62 PSI on the gauge. All in all, it's a good suggestion, it wouldn't hurt to replace it since the truck has 192000 some miles and that hasn't ever been switched. Any other ideas? 

[Mike GMC]

You might look at the idle air control valve and the intake air temp.sensor.

[sdeeter19555]

Clean the throttle body/plate lately?

2012 2500hd 6.0l CCSB 4wd

[PrairieGM]

Mike, that's a good idea I'll check those, thanks

 

sdeeter, no I have not. That would be a good idea, l should of done that when I was checking the air intake tube. It's been a little tough, as I've been up at college with no place to work on it except the parking lot. Thanks for the advice.