86 f150 erratic idle
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Joined: Jul 2005
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86 f150 erratic idle
this vehicle has the EEC 4/ efi system. initial problem was fuel pressure regulator letting fuel dump right into intake manifold through vac line, replaced regulator problem solved. now motor wants to idle between 1200 and 1600 rpm in park or neutral way to high for my liking. question, what is correct idle at normal operating temp? and what is possible cause bad egr, evp sensor, solenoid valves, and can any of these be tested individually. thanks. gotta say this is an excellent site with lots of helpful members.
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Joined: Feb 2006
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I had a 1990 302 (w/eec) that had a similar problem. At a stop light or when idling in the drive-way, it would rev up so high that I though it was going to blow up. I started by pulling vacum lines off and plugging them with my finger. I pulled one of the lines, and when I plugged it, the truck idled right down to normal. I found a tiny pinhole in that line. Replaced the line, and the problem stopped. Hope this helps.
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Joined: Jun 2004
Posts: 353
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From: Mid-Missouri
I would tend to agree. Check the joint between the upper plenum and the intake manifold as well. The upper plenum is aluminum and the intake is cast iron. The metals expand and contract at different rates and this eventually causes the paper gasket to deteriorate. The process is helped along by the fact that this area of the engine experiences some wide temperature swings as the engine warms and cools.
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