1991 Toyota Pickup intermittant idle issue

1991 TOYOTA PICKUP
168,000 MILES • 4 CYL • 4WD • MANUAL
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CELTICRIDER
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  • 2 POSTS
My toyota pickup has an intermittant idle stumble. I have replaced the spark plugs, plug wires, pcv valve, fuel filter, air filter, thermostat, cooling fan, temp sensor, cold start injector sensor and nothing has helped. After driving for awhile, sometimes when I come to a stop the idle will sit at 900 and then quickly drop to 400 - 500 then slowly climb back to 900, then repeat over and over again. Any ideas what to do next?
Jan 12, 2009 at 10:03 AM
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KHLOW2008
  • ✓ASE Certified Mechanic
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Hi celticrider,

Did you try to retrieve for Diagnostic Trouble Codes?

Was the Check Engine Lamp showing?
Jan 14, 2009 at 9:56 AM
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CELTICRIDER
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There is no engine lamp on or codes present.
Jan 14, 2009 at 10:01 AM
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KHLOW2008
  • ✓ASE Certified Mechanic
  • 41,814 POSTS
  • ASE Certified Mechanic
The engine uses a Air Flow Meter and the symptoms you described could be due to 1. Vacumn leakage between AFM and throttle body. 2. Valve clearances too tight. 3. Idling speed adjusted too high. Idling speed should be 750 rpm at operating temperature.


https://images.2carpros.com/forum/automotive_pictures/192750_IdleScrew90Pickup_1.jpg

Jan 14, 2009 at 10:37 AM
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