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Question
I recently sent a question regarding my 2002 GMC envoy slt 4x4. You told me I didn't tell you how many miles so now I'm replying with more information.  I asked if a tune up would solve why my car has been idling roughly every so often when I'm stopped at a traffic light, it is really noticeable when I take off and accelerate from a traffic light or stop sign . It has 143000 mile's on it. There are no kind of smells when it happens just hesitant when I accelerate for not even ten seconds then its fine. There are no kind of check engine lights or service engine lights at all. Other then this it drives fine. Worries me because I just dropped about half a grand to basically get all new parts for the front end and I'm not trying to dump ll of my $ into this vehicle. Please let me know. Throttle body has been cleaned and I have a fuel & air filter & plugs & boots I'm getting put on this week, but from talk on these kind of  sites people replace all of this and the problem please help!

Answer
Hesitation when starting out has to do with the air-fuel mixture, almost always.  Sometimes it's an O2 sensor, sometimes it's other problems, but it's nearly always something that changes the air-fuel mixture one way or another.  The O2 sensors always trigger a check engine light, so it's not those.  It's possible it's a crank position sensor starting to go funny but not enough yet to turn the check engine light on, so that's something you could have checked. There is a slight possibility it's one or more spark plugs partially fouled so they fire when you get going but misfire when you are just starting out, so having the plugs changed may help, and may possibly even solve it for you.  It could even be bad wires, so I'm feeling pretty good that you are getting new plugs and wires.  Your idle control valve would have a symptom like that if it was dirty or defective, so you could check that.  One or more leaky injectors would cause that symptom, so you could have those checked.  Just find another Envoy and trade injectors with them, see if the symptom follows those injectors.  I wouldn't buy new ones because they are rarely the problem and you most likely don't need them, but it's worth checking.

If your plugs and wires don't solve it, then get back to me with any new details that show up.  I'd like to help you get it figured out and if you do find the problem I would really appreciate you letting me know what it was, for my education.  Thanks for choosing me.  Please stay in touch until we get this done.  :-)

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