Coming off a 250 mi trip with no problems, when at a stoplight, engine RPM becomes erratic and fluctuates between 1000 and 2500 RPM with associated stumbling on acceleration. No problem at idle, and after being driven slowly the problem goes away. at speeds up to 50 mph,, only to return on acceleration or going uphill..
SOURCE: Engine pulsates during idle and from second to third gear
Try checking for vaccum leaks, use carb cleaner and spray it around the base of carb, vaccum hoses, edges of intake manifold, take pliers and squeeze the big line to brake power booster & see if it changes, pull the pcv valve out and cover with your finger see if it changes idle.
SOURCE: engine starts,reaches high rpm,then slowly returns
Vacuum leaks. Check all hoses and intake bolts. Leaking EGR or plugged PCV valve. Air filter plugged. Leaking head gasket. Worn timing chain. Camshaft lobes worn. Valves burned or leaking. Fuel idle control system or sensor. Good luck!
SOURCE: 2001 2500hd duramax idle surge. doesn't do it all
Well there are quite a few things that casue a "surge" in a common rail diesel. You will need to check injector flow rates (scanner only). Fuel pressure regulator for pulsing (scanner only). Supply side fuel system for air leaks (seeing if it is sucking air into the system).
My bet would be the injectors, because you say the rpms aren't going up and down, which is usally what happens when the regulator goes bad, and when you **** air into the supply they have an extended crank. Report back with your findings.
It can be issue
with IAC( idle air control valve) causing the problem.
There
are many other possibilities causing these idle issues. Engine idles rough.
There
are few help links with solutions to troubleshoot such idle issues.
I
suggest you refer the link below and follow
its troubleshooting details:------
Click
the link below:-----
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http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html
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http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html
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http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html
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http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html
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Cold start problem and vehicle shudder around 2500 to
3500 rpms
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http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html
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http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html
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http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html
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http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html
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http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html
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http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
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High
Idle Problem
http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html
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http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html
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http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html
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http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html
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http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html
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http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html
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http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html
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These
details will help.
Thanks.
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