Please help with idle problem.
 

I need some help and advice on my truck, I have a 1999 2500 4WD extended cab long bed Silverado with the 6.0-liter engine. The problem is I have a service engine soon light on and the truck will not idle correctly. It oscillates between 500 and 1100 RPM while at a stop, there doesn’t seem to be any problems running the truck at normal city and highway driving. I took the truck to AutoZone to get the error codes; they are P0171 and P0174, which seem to point to the either a MAF or Oxygen sensor telling me the truck is running lean. The guy at AutoZone was pretty sure the problem was in the MAF when he saw the second code. He suggested that I clean the sensor with this cleaner and described it to me where it needed cleaned.
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Well I cleaned the sensor and this did not help, when I looked at the sensor it had 3 very small wires that some how measured the air. I read on a web site (GM Chevy) that you could start the engine and let it run and tap on the MAF and if the truck idle jumped around then the MAF should be changed, well I did this and it didn’t seem to work.
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Your help would be greatly appreciated if you could help or if you have had the same problem and be able to point me in the right direction. I don’t have the money to start replacing part one at time in hopes to find the problem. With these cars today it seem you need to have a lot of equipment to identify what the problem is with it.

Red

Even though it didn't react to the tap test I would still replace the MAF sensor. It could still be responding sluggishly enough to throw the whole balancing act of fuel/air off enough to cause problems.

Does it do it mainly when it's cold or all of the time?

It has done it since mid October but seems to have gotten worst as it gets colder.

Its very frustrating, I used to be able to work on cars but today with all the sensors I don't know what is causing the problem. I'm by no means a mechanic but my background is electronics. I could test the sensors by applying different voltages but I don't know what to expect or should get on the output.

you have a vacum leak take some carb cleaner and spray the intake and throttle body and if the idle goes up where your spraying thats where the leak is check all rubber hoses plastic elbows your getting air in somewhere thats why its getting a lean code