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Discussion Starter #1
It surges/stumbles at idle badly about half the time lately.
I don't have any lights coming on to indicate I have codes to read. Should I try to pull some anyway?

What could be the issue?

It has 117k miles, we just bought it a couple of months ago, meticulously maintained by the second owner.

I've done some searches, but most posts seem to be about the older TBI engines and nothing within the generation of engine I have.

thanks in advance for your help.
 

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Discussion Starter #2
this morning I drove it to work (it's my wife's car) and noticed that it does it going down hill when using cruise control. It did it at 67mph and 45 mph with the cruise on, only noticed when it should be coating or partial throttle down a slight grade (gently rolling hills?)

---------- Post added at 10:54 AM ---------- Previous post was at 10:53 AM ----------

also found out today that 2 different code readers showed "Not connected" when hooked up to the diagnostic link doodad thingy.
That's not very helpful. I wonder what that problem could be.
 

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Check the fuse for the OBDII port. Also a big problem with these trucks is carbon build up in the Throttle Body so removing that and using a good throttle body cleaner may solve the issue.
But also make sure you get that OBDII Port connected since you never know when you will need it!
 

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this morning I drove it to work (it's my wife's car) and noticed that it does it going down hill when using cruise control. It did it at 67mph and 45 mph with the cruise on, only noticed when it should be coating or partial throttle down a slight grade (gently rolling hills?)

going down hill with the cruise on isnt uncommon for the surging, when at times the surging is because the vehicle is at a speed in between coasting and having to apply some throttle to maintain speed. i notice it mine at certain speeds as well going down hill in cruise. now if it is doing it in normall driving/cruising/idle conditions that is something more of a problem. as Mike said check the fuse for the OBDII port
 

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Discussion Starter #6
cig lighter fuse was blown. I'll run by the shop again on the way home and let them try to scan it again, hopefully with it idling and surging.

The surging while coasting isn't normal, not to the degree it's doing it on my vehicle. You can tell something is out of whack.
 

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You mentioned that it was meticulously maintained, but I would check the fuel filter anyway. Pretty inexpensive maintenance item for peace of mind. Murdog set me straight on the MAF and throttle body cleaner for me a few months back and that worked wonders for me as well. Definitely worth a shot.
 

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Discussion Starter #8
I finally got around to cleaning the MAF and throttle body tonight. It wasn't surging today before I cleaned it, and hasn't surged afterward.
It's not real predictable, but i would have thought it would have been surging the irst time i started it up today, which is the first time in several days.

One thing I did notice today was that it has a really dead spot right when you give a quick tap on the throttle. Almost has a sucking sound.
NOt sure what that is, but I'd like to know. It runs great otherwise, but that dead spot/hesistation is a bummer. I wonder if it's related to the surging.

I haven't check the fuel filter yet, as recommended above, but I'll take care of that this weekend.

Any idears?
 

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I'd check for a vaccuum leak. I'm not sure if you have a external fuel filter, my friends '03 Silverado 1500HD doesn't have one. If you do then its on the inside frame rail under the drivers door.
 

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Discussion Starter #10
That major dead spot had me thinking maybe a vacuum leak. I'll have to look it over and see what I find. I wonder if they are notoriously for vacuum leaks in a certain area?
 

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Sorry can't answer that.
 

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When you start up your truck check to make sure your engine light comes on. I have heard of people putting a needle through the dash to break the bulb or just flat out removing the bulb. With over 100K I would check that all the 100K mile maintenace has been done as well. Run some seafoam through the intake, and in fuel system, and definetly take off your throttle body to clean it, did mine at 106K and I noticed a improvment on idle.
 
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