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Unusual Idle 2004 Chevy 1500
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players ltd.
New User
Nov 19, 2011, 10:43 PM
Post #1 of 8
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Unusual Idle 2004 Chevy 1500
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Hello and thank you for reading and perhaps addressing my first post. I look forward to making good use of this resource and hopefully somewhere along the way I can give back by providing some input of my own.
For now I have a question about my Chev. It arose today and I have not tried anything yet to address it-
Year: 2004
Make: Chevrolet
Model Silverado K1500
Engine size:4.8L V8 4wd, automatic
Mileage: 90k
My idle is fluctuating between normal (about 600 rpm) and low (about +/-300 rpm). Its not quite to the point where it feels its going to cut out but it gets your attention. It shakes a little while going through these motions. Happens after running a little and continues at most if not all stand stills. As far as I can tell combustion seems fine when I open the throttle to any degree.
Engine light came on a couple weeks ago but this is normal with this vehicle and often solved with a fresh full tank of gas. I havn't topped up to full yet but I am not terribly concerned that the issue is related as the engine light being on is a common part of this vehicles history and nothing has ever come up on a diagnostic when I've looked further into it.
So, isolated idle problem i am hoping. Truck is 100% other than this and has not a whiff of engine misfires or mishaps in its history.
What I plan on looking at in order of simplicity-
Air filter
Fuel filter
Spark plugs
If those don't solve my problem, what I think I should have a professional mechanic analyze-
Diagnostic
Timing
IAC valve
Vacuum lines
O2 Sensors
Am i on the right track? Can anyone add and provide any expertise and/or theories?
Any help is appreciated
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 20, 2011, 12:32 AM
Post #2 of 8
(6257 views)
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Re: Unusual Idle 2004 Chevy 1500
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Hmmmm? A diagnostic showed nothing! It needs a better grade of code reading and diagnostics. 300 RPM for whatever the cause should have set a code.
Engine light and refueling suggests to me that perhaps something with evaporative emissions isn't right. IMO nothing wrong with replacing fuel and air filters but probably not the source of the trouble. Vacuum leak(s) from anywhere, hoses or gaskets will confuse engine controls,
T
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players ltd.
New User
Nov 20, 2011, 12:47 AM
Post #3 of 8
(6252 views)
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Re: Unusual Idle 2004 Chevy 1500
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Thanks for your reply but I think I was unclear.
Long before this recent idle issue, in the past when the engine light came on, a diagnostic test revealed nothing and the mechanic thought it may be an issue with the fuel cap. A full tank of gas later and some fiddling with the fuel cap and voila- the light went off. It has repeated with no pattern, just comes on sometimes (3-4 times a year). I fill up to the brim, fiddle with the cap seal and it goes off- works every time.
The light is on now but I have not been to fill up and fiddle the cap, no reason just havn't bothered yet. A short while later (today) the idle starts acting up. Due to the separate timing I suspect the two are unrelated.
Just thought I would mention the engine light to provide any and all info. Sorry if unclear.
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Sidom
Veteran
/ Moderator
Nov 20, 2011, 1:15 AM
Post #4 of 8
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Re: Unusual Idle 2004 Chevy 1500
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Since the new problem popped up, it would be a good idea to have the codes pulled again, it's very possible a new one you haven't seen yet came up....
A good maintenance suggestion would be to clean the throttle body with some throttle body cleaner and a small brush. This way a dirty throttle body can be eliminated as a possible cause of the problem...
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players ltd.
New User
Nov 20, 2011, 1:21 AM
Post #5 of 8
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Re: Unusual Idle 2004 Chevy 1500
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Okay, will do. Thanks
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Tom Greenleaf
Ultimate Carjunky
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Nov 20, 2011, 2:33 AM
Post #6 of 8
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Re: Unusual Idle 2004 Chevy 1500
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Just to add: Thanks for jumping in Sidom. I'd probably just replace fuel cap just because "fiddling" with it makes some difference. If not tied to the vehicle any chance of a mix up could make a difference but don't think it would cause low idle,
T
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Hammer Time
Ultimate Carjunky
/ Moderator
Nov 20, 2011, 7:04 AM
Post #7 of 8
(6235 views)
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Re: Unusual Idle 2004 Chevy 1500
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For sure you need to have the codes read. There are hundreds of different possible codes and they do not just come on for no reason. There is always a reason. The tech may not be successful in finding the cause, but that is not the car's fault. The problem is still there.
You may have a bad IAC ( idle air control) but try eliminating any vacuum leaks and cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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samg.
User
Nov 20, 2011, 7:34 PM
Post #8 of 8
(6219 views)
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Re: Unusual Idle 2004 Chevy 1500
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There is a bulletin for low idle codes, check the throttle body.
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