oscillating idle
Thread Starter
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Mountain Pass
Joined: Apr 2005
Posts: 105
Likes: 1
oscillating idle
I have a 1988 Ranger, 2.9, auto. with an oscillating or rolling idle that ranges up and down about 100 rpm. No DTCs are displayed. Has anyone had a previous experience like this and/or a solution? All suggestions are welcome. Thanks
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Post Fiend
Joined: Jul 2005
Posts: 8,462
Likes: 4
From: Durant, OK (SOSU)
Is there an idle air control valve on the 2.9L?
Little metallic cylinder on the side of the throttle body on most of the later engines, including the 4.0L, which is a derivant of the 2.9L in many aspects.
RP
Zach
Little metallic cylinder on the side of the throttle body on most of the later engines, including the 4.0L, which is a derivant of the 2.9L in many aspects.
RP
Zach
Moderator
Joined: Jan 2004
Posts: 13,851
Likes: 111
From: SW Va
OK Dan, well we'll need some more detail & hints to try & zero in on this one.
On idle problems, a long typical list of things to investigate are, throttle body or carb, fastner tightness & gasket/s condition, vacuum leak/s, vacuum hose connections & vacuum hose condition, pluged PCV valve or hose, clogged air filter, fuel pressure, leaking head, or intake manafold gasket, secondary ignition system problems, like worn plugs, with spark gap erosion, or dirty internal/external insulators, leaky spark wires, maybe even cracked insulstion/leaky coil or coilpack, worn camshaft lobes.
So maybe a visual check out of the vacuum hoses, then monitor the intake side with a vacuum gauge, a fuel pressure check & a compression check, would help narrow things down some.
Let us know what you find.
On idle problems, a long typical list of things to investigate are, throttle body or carb, fastner tightness & gasket/s condition, vacuum leak/s, vacuum hose connections & vacuum hose condition, pluged PCV valve or hose, clogged air filter, fuel pressure, leaking head, or intake manafold gasket, secondary ignition system problems, like worn plugs, with spark gap erosion, or dirty internal/external insulators, leaky spark wires, maybe even cracked insulstion/leaky coil or coilpack, worn camshaft lobes.
So maybe a visual check out of the vacuum hoses, then monitor the intake side with a vacuum gauge, a fuel pressure check & a compression check, would help narrow things down some.
Let us know what you find.
Thread Starter
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Mountain Pass
Joined: Apr 2005
Posts: 105
Likes: 1
Sorry for the delay but only have computer access occasionally. It is fuel injected w/IAC. I am in the process of a tune up as we speak. I will check the intake system bolts for tightness and vacuum lines for leaks. Thanks for your response.
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Post Fiend
Joined: Jul 2005
Posts: 8,462
Likes: 4
From: Durant, OK (SOSU)
Pull and clean the IAC while you're in there. As I said, it's known get dirty then cause the idle to oscillate, idle too low, idle too fast, etc. After the tune up, start things up, sometimes you'll fix it without knowing it.
RP
Zach
RP
Zach
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Mountain Pass
Joined: Aug 2003
Posts: 226
Likes: 8
From: southwest washington (th
maybe others can correct me here, but i have the same year ranger and engine and i bought it brand new and it always had a rough idle of maybe 50 to 100 rpm! when i test drove it and noticed it the salesmen said oh they all do that! i said right so lets check a few more out!!! and every single one i drove did the same thing! so after 300,000 miles i guess it wasnt much of a problem! hope this helps!
