If it is stuck open, no idle......If stuck closed, spark knock during acceleration.........
SOURCE: what are the symptoms of a bad egr valve ina 1994 geo tracker?
this may help
EGR Theory. EGR serves one purpose and one purpose only. That purpose is to reduce Oxides of Nitrogen (NOx). Undernormal combustion, Nitrogen(N2)Oxygen (O2) in the air and Hydrocarbons (HC) in the fuel combind into water(H2O) Carbon dioxide (CO2) and the Nitrogen remains unchanged. Under very hot combustion temperatures, the Nitrogen reacts with the other two byproducts and forms Nitrogen oxide (NO). After being released into the atmosphere, it picks up another Oxygen and becomes Nitrogen dioxide (NO2). In the presence of sunlight,
it combines with other compounds like Hydrocarbons and forms Smog. Since exhaust gas is inert (very stable) it doesn’t burn again. So by being introduced into
the combustion chamber, it will lower combustion chamber temps enough so that
the Nitrogen doesn’t react with the other compounds and is passed unchanged out
the tailpipe thus not contributing to smog. Now, since exhaust gas doesn’t burn, it
doesn’t exactly help with combustion. At higher RPM’s, this really isn’t noticable,
but at idle, the reintroduction of exhaust gas will cause a very rough idle and can
cause stalling if to much is introduced into the combustion chamber
SOURCE: malfuntion light coming on...egr valve may need replaced
the range from a simple sensor issue with no symptom except a check eng light to a rough idle with a light.
SOURCE: what are the typical symptoms of a bad egr valve
A vacuum leak at the egr valve can cause rough idle and almost stalling condition.
A non functioning egr valve that is plugged up won't affect driveability, but NOx will be in the exhaust at normal operating temperature which may not be good for an emissions test if they test for that in your area.
Good luck on this repair.
SOURCE: 95 check s-10 blazer idle
An EGR that is stuck opencan very well cause the symptom you are decribing, including surging at idle and poor acceleration.
Failure of GM EGR Valves is quite rare.
A common problem on the 4.3L Vortec engines is failure of the Central Multiport Injection Assembly located between the plastic upper intake plenum and the lower intake manifold.
Sometimes failure of injector lines and/or the fuel pressure regulator (Part of the MFI Assembly) will cause fuel to spill into the upper plenum area. This can dislodge carbon deposits in the upper plenum which then get stuck in the EGR Valve and cause the symptoms that you are describing. The EGR Valve can be removed and cleaned. Replacement is not usually necessary.
Ido recommend replacement of the injector assembly however.
check out this solution page for more info regarding this.
http://www.fixya.com/cars/t3218505-misfire_code_rough_idle_full_tune_up
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A bad one creats a hidden vacuum leak. It may hav worn connection on xhaust. If u can blow into it then u pribly need newone or used from junkyard
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