codes p0171 & p0174

[airsslt24]

I have a 99 chevy silverado and i pulled up codes p0171 & p0174. System is running too lean. Its an intermitten code that seems to come up when its realy cold outside / early in the morning. It idles realy rough when cold but runs just fine when it warms up. This leads me to believe that its not an o2 sensor because the pcm doesnt even register the 02 sensors until they get warm, and my rough idle goes away when warm. Is this enough justification to rule out the o2 sensors. and since it works fine when warm, then can i rule out the sensors including MAF? It doesnt seem like its missing so i can rule out the injectors / spark plus and wires, right? or am i going about this all wrong? recently had my fuel system cleaned, new fuel filter last year around this time for same problem. It seems to help but doesnt seem to fix it.

[airsslt24]

Help!!

[777stickman]

Both those codes indicate a lean condition on both banks. My 1st thought is a vacuum leak. Could be hoses, intake gaskets?? Also an exhaust leak up stream of the O2 sensors can cause this..........Steve

[WalrusInc]

Need more info bubba. When was your last tune up? Whats the exhaust smell like? When you say recently cleaned fuel system, how long ago, and what brand of fuel are you using? Are your O2 sensors switching properly? 171 and 174 codes can be quite the pain, so I hope you've caught it or will soon.

[listenloud]

My chack engine light came on. When I tried to read the codes the scanner wouldn't connect. The fuse marked "cigar" powers the diagnostic connector. It was blown. When I replaced the fues I was got codes 0171 and 0174 in my 2000 Silverado. The codes would set twice everytime I cleared them, so I had 0171, 0174,071, 0174. Without even looking around under the hood I began reasearching the possible cause. When I finally opened the hood and looked at the engine I noticed the air intake tube from the air filter housing to the mass air flow had came disconnected at the mass air flow. I reconnected to air intake and cleared the codes.

No more codes! Simple problem to fix.

[rjeffery]

I had a 99 ford exploder that did the same thing. What happened is that when it got cold, the intake gasket would contract, causing a rough idle and throwing a code. Might be somthing to look in to.