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My Suburban started doing something odd on starting before, but I'm not completely sure how to describe its behavior.

It get's past the battery part fine when it's starting, and the starter motor is new, so that part sounds perfect and is always quick, but what happens is right when the motor is starting every once in a while it has a very slow and sluggish sounding start, like once the motor is on it takes a few seconds to get back to sounding correct.

It does this seemingly randomly, in any weather condition (wet, hot, cold, etc.) and it's got about 216,000 miles on it. What could this be?

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Goodness, this could be just about anything.

  • What setting is the heater, ventilation and Air Conditioning (HVAC) set at? I'd expect this as normal if the A/C compressor is engaged (which it is in normal A/C modes, plus defrost and defog modes...)
  • I wouldn't necessarily expect fuel related issues with this description, but it would be nice to see if there are any engine diagnostic codes stored in the engine management computer. The one area of concern is how this engine manages cold start functions. You could have a slow idle bypass function control system. Its also possible that area of the intake system is dirty and gummed up. Normally I'd expect to see diagnostic codes, but dirt and grime causing a slow controller might not set a code.
  • Spark is a possible issue. If you've got old spark plug wires, and they are grounding out, who knows how that will look.
  • I'd like to know if there is a vacuum leak from old split hoses anywhere on the top of the engine. I'm particularly interested in the lines that run to the Exhaust Gas Recirculation (EGR) system. Its best to take a while and physically examine each and every rubber line in the engine compartment.
  • Its possible you've got a problem in either the EGR or the Carbon Cannister bypass system, but problems there should set a code.

I'd sure like to see the results of a code test (free at many autoparts stores) and the results of a vacuum hose cracked or broken review.

  • Air conditioning I almost always have turned off, along with the fans so that shouldn't be causing any problems. But that's quite a list, I'll definitely have to take some time this weekend and check these things to the best of my ability to see if I can figure this out, because when it does this it really sounds like it's the last time it's going to turn on – Brian Leishman May 23 '16 at 17:08
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    I'm pretty sure you probably knew that, but I only mention it because the A/C is also engaged automatically in Defrost and Defog modes. Many folks are not aware of that. – zipzit May 23 '16 at 17:10
  • I'm leaning towards an EGR issue, such as it being sticky, but not stuck. If a sticking EGR were stuck open (or partially) when it shouldn't be, yet comes back to where it should be after startup, this type of issue might present itself. Just throwing it out there. BTW, @zipzit - Great answer! +1 – Pᴀᴜʟsᴛᴇʀ2 May 23 '16 at 21:11

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