96 silverado high idle speed - Truck Forums

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Old 01-28-2009, 07:46 PM
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Join Date: Jan 2009
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Default 96 silverado high idle speed

got an annoying problem 5.7vortech
my 96 k1500 z71 silverado is idling at 1500-1700rpm hot or cold. when driving and i slow down for a stop the engine races at 1500+ rpm until i come to a complete stop, then it will idle down to 700rpm. But if i then switch it into park or neutral, the rpm's will increase back up to 1500 before settling back down to 1000rpm. This has been getting steadily worse and now the truck seems to hesitate intermitently while driving in the city, like something is backing off the throttle speed.
things i've done so far....
new cap rotor wires
new tps
new iac
new plugs
sprayed the intake from above with ether, no change in idle.

also, there seems to be alot of vacuum coming from the oil fill tube. i have seen blowby before but not a vaccumn of air in the crankcase.

don;t see any black smoke from the tailpipe....so not rich

any ideas at to what's causing this to happen?
it's really getting hard to slow this truck down for stop signs and stuff.

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Old 01-28-2009, 08:25 PM
chrisbmo2000's Avatar
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Join Date: Jan 2009
Location: Columbia, Mo
Posts: 983
Default RE: 96 silverado high idle speed

check engine light or ses light on? what does the PCV valve look like?
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Old 01-29-2009, 06:52 AM
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Join Date: Jan 2009
Posts: 2
Default RE: 96 silverado high idle speed

pcv is new too, and sucking air like it should. when i take the cap off the oil fill tube, the engine almost dies. can the pcv suck sooo much air from the crankcase that it would create that kind of vaccuum from the oil fill tube?
all the carbuerator cars and trucks i have owned don't have anywhere near that kind of vacuum in the crankcase, even with the pcv system.
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