high idle
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More Turbo
Joined: Apr 2018
Posts: 743
Likes: 59
From: pine city washington
high idle
i probably have a thread on this but i cannot find it. the truck fires right up then jumps to 3000 rpm according to the tach. i have cleaned the throttle body, changed the coolant temp sensor, disconnected the spout and that brought it down to 2500, it runs smooth and fires right up. i sprayed carb cleaner around the base of the intake, no change, u even unplugged the idle control, no change. it revs up fine, i know it probably has a blown head gasket by all the white smoke and the pressure in the radiator after 1 minute. would that cause a high idle?
Logistics Pro
Joined: Aug 2010
Posts: 3,717
Likes: 585
From: Chillicothe
Head gasket issue shouldnt cause an idke issue. What year and transmission? I know its most likely the e4od, but if its a c6 the vacuum modulator may be bad and atf burns white.
Also, pull and plug the brake booster hose to rule out a vacuum leak there.
Also, pull and plug the brake booster hose to rule out a vacuum leak there.
Cargo Master
Joined: Jun 2002
Posts: 2,033
Likes: 32
From: Aurora,Colorado
The gasket between the upper and lower intake manifold can cause a high idle if defective and letting air bypass the IAC. Also disconnect the electric leads to the IAC and see if the idle changes.
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More Turbo
Joined: Apr 2018
Posts: 743
Likes: 59
From: pine city washington
i tried disconnecting the leads on the idle control not a whit of change. i have a blown head gasket, i hope, so i need to change a few gaskets
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Hotshot
Joined: Jun 2015
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I’m fairly certain that when you replace the intake manifold gaskets in the process of replacing the head gaskets is when you will fix the vacuum leak.
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More Turbo
Joined: Apr 2018
Posts: 743
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From: pine city washington
found part of the problem. four of the lower intake bolts were tight the rest were just sitting there covered with grease and oil. the rest of the bolts on the engine were not very tight. i took them off with a 3/8 ratchet. drivers side had blown gasket and no.5 exhaust was burnt. got that head fixed for 50 bucks now on to the passenger side.
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