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My 2004 Tahoe is not running well and conked out on me the other day. I just had it repaired for some other reasons and the repair shop suggested we needed to have spark plugs replaced so it will run better. However, before then, it ran fine. I said no on the spark plugs, but now that I have it back it is running poor and I don't know how to describe it... It is glubbing, missing, on the verge of conking. The same thing happened to our minivan years ago and in that case, it was simply an air flow tube that was not pushed in all the way and once we pushed it in, all was well again.

  • When was the last time spark plugs were replaced? The plugs it self are not that expensive, but in some v8 engines they are harder to access. Might be a good idea to get the plugs replaced if they are easy to access. – rana Dec 8 '15 at 21:32
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    I don't think ever @rana. – CRAIG Dec 8 '15 at 21:33
  • Please help us help you by hooking it up to a scan tool to see if there are any codes and understand what the fuel trims are like. I'd recommend inspecting the spark plugs to see if they really need replacing before splurging money on brand new ones. – Zaid Dec 8 '15 at 21:35
  • How many miles on your Tahoe? If over 100k, you need to do a complete tune up, to include plugs, wires, and O2 sensors, then cleaning all of the MAF and IAC valves. The 2004 GM Trucks had a 100k tune up for these items, so is why I am suggesting them straight out. Also, a video of what it's doing would be of great assistance ... one with good audio. AND as @Zaid said, get it scanned so you know what's going on. – Pᴀᴜʟsᴛᴇʀ2 Dec 8 '15 at 22:01
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    +1 for "glub glub glub" - I can hear the sound in my head perfectly! ;-) – Bob Cross Dec 8 '15 at 22:43
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The most common cause of this complex of symptoms is leaking intake manifold gaskets. Test for this by spraying a squirt of carburetor cleaner up and around the intake manifold. If the engine smooths out for a few seconds then there is a leak.

The second most common cause is failure of the mass air flow sensor (MAF). I offer no quick tests for this part short of swapping in a new one. Testing is done with graphing scan tool data and having an experience person interpret this data.

Other failures of possible, but this covers 90% of the problems of this type on this engine.

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