Every 3 to 4 weeks, my 2011 Sierra 2500HD Diesel goes from a normal idle of about 600 rpm to 900 rpm. Fuel mileage drops. It might last 50 miles or more. Any idea what is causing this issue?

SOURCE: 2003 GMC Duramax Diesel won't start

I see that you had the injectors replaced 20,000 miles ago. I would still check the oil to make sure it is not overfull. The new injectors could be bad. If the oil level is not overfull then get a paper towel and touch the dip stick tip on the paper towel while oil is on the dip stick. If it's only oil it will not spread. If it has diesel in the oil the oil with spread. If this test doesn't show the injectors to be bad then you have three other possibilities. The FICM (fuel injection control module), the fuel pressure regulator, or the injection pump. It's hard to pinpoint what the problem is without running more tests and the only way to run those tests is with the computer the dealership has. Just so you know your injectors are still under warranty until 100,000 miles. Most likely you will have to take it to the dealership to get you truck fixed. I hope this helps you some.

Wade Cook

• 6 Answers
• Posted on Jan 27, 2009

SOURCE: 4X4 inop on 2003 GMC Sierra 2500HD

I have found that when you are going to engauge 4x4 high, it is best to only be going about 3 miles an hour. Not faster, not stopped. It likes some movement to help it mesh. I've had perfect shifts since I started this. Hope it helps. Wade.

SOURCE: I need to know how

check owners manual,or call a gm service dep.

SOURCE: ac is blowing warm air in my 2005 sierra 2500hd duramax. Any idea

Your system has R-134 Freon in it. the 134 is made up of smaller molecules than the old R-12. The R -134 permeates through the rubber parts of the system. If the system gets too low on Freon, the compressor will stop coming on.(low pressure cut out switch). Have the system serviced with an A.C. machine that can vacuum, measure the amount of Freon in the system, and add the right amount. The machine can also inject die. Later the die will show up under a black light.This will show any leaks you may have.

SOURCE: 98 chevy cheyenne king cab 4x4 diesel 6.5 dually.

Ditto? TCC (torque converter clutch solenoid on the way out or already kaput...?