2002 Chev Tahoe Runs really rough especially when cold, stalls, when first start it will suddenly kick into high idle 200rpm then back to normal. While driving seems ok until you slow down for a light start to bog then stalls. Engine light somethimes stays on. Other times doesn't come on at all. Codes P171 and P174 come up.

SOURCE: rough idle stalls at low rpm's

hello first check your idle with the car running foot on brake see were your rpm reading is if your below 500rpm check your label underhood for your curb idle setting second see if theres a adjustment screw you can increase were your gas cable lever rest against your set screw underhood if you feel confident enough remove your iac motor idle air control valve if the bore were the end of the pintle extracts out to close has varnish builup our carbon it will stick creating vacuum leak type senario causing stalling rough idle sometimes even no start conditions good luck

SOURCE: Check Engine Light On

have the 02 sensors checked

SOURCE: engine stalls after cold start-up & release from high speed idle

I had a similar problem.  I found the filter cartridge below the pcv valve had carboned up, and after the crank case pressurized, oil was forced out the pcv supply line to the throttle body.  The idle air control valve solenoid got oil in it and caused my problem, but only when it was cold.  The pcv cartridge is accessed by removing the pcv valve and the rubber fitting that the pcv valve mounts in.  It can then be fished out with a pick set, and it is a pain because you can't see it, but you can get you hand back there.  I hope this helps you.

SOURCE: I have a 2003 GMC Denali with Codes P171 &

More likely it's the intake manifold gasket leaking. They can become flat and **** air in passed the gasket, causing a lean condiiton.

SOURCE: 99blazer s10 trouble codes p171/p174

P0171 - System Too Lean (Bank 1)
Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

A code P0171 may mean that one or more of the following has happened:

• The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
• There could be a vacuum leak downstream of the MAF sensor.

• In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
• Inspect all vacuum and PCV hoses, replace if necessary
• Check for a dirty fuel filter and proper fuel pressure