Idle oscillation
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Idle oscillation
Has anyone experienced idle oscillation where the car will not idle smoothly but constantly idles up and down? When I turn on the A/C it smoothes out but then starts again. I checked for vacuum leaks and didn't see any. Has anyone experienced this?
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Re: Idle oscillation
Two possibilties:
1) Idle Stabilizer Valve is bad or sticking.
You can clean it using carb cleaner.
2) Bad or mis-adjusted idle switch. This switch should just make contact when the throttle is in idle position.
For a test, run the car with the electrical connector to the ISV unplugged. If the problem goes away, you'll know it's one of those two things.
1) Idle Stabilizer Valve is bad or sticking.
You can clean it using carb cleaner.
2) Bad or mis-adjusted idle switch. This switch should just make contact when the throttle is in idle position.
For a test, run the car with the electrical connector to the ISV unplugged. If the problem goes away, you'll know it's one of those two things.
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Here's what I found...
When I started it cold today, it ran and idled around 900 rpm with no oscillation. After a while when it was running for a while, the oscillation started. It would idle, but fluctuates over about a 50 rpm range 2 times every second. When I shut off the engine and re-started it, it would stall and not idle at all. I had to keep my foot on the throttle to keep it running.
Disconnecting the ISV electrical connector, the rpm increases and the oscillation is still there.
Disconnecting the idle switch, the idle increases even higher and the oscillation dissapears. I have tested the switch and the connection is good and I can hear it click when opening and closing the throttle.
Let me know if this indicates anything to you.
Disconnecting the ISV electrical connector, the rpm increases and the oscillation is still there.
Disconnecting the idle switch, the idle increases even higher and the oscillation dissapears. I have tested the switch and the connection is good and I can hear it click when opening and closing the throttle.
Let me know if this indicates anything to you.
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Re: Here's what I found...
I had the same problem on my '85 5KS. It turned out to be the wires on the connector to the FOT/IDLE switch. They were broken inside the insulation under the rubber boot where they enter the back of the connector. Someone with a Bently manual can probably tell you what the reading across the conector terminals should be. My break was right at the connector....easy to find.
Good Luck
Good Luck
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Re: Idle oscillation
The ISV is on top of the engine. It will have a hose or steel tube comming from the crankcase, and also an electrical connector going to it. The Idle switch is on top of the Intake Manifold and the Full Throttle switch is under the I.M. One electrical conn. serves both switches. The idle switch tells the computer when to regulate the idle. The ISV allows additional air to enter the intake manifold to adjust the air/fuel mixture.
If you need specific info, post it on this list.
Good Luck
If you need specific info, post it on this list.
Good Luck
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Have you solved your problem?
I still have the oscillation with mine. I disconnected the ISV electrical connection but the oscillation is stil there. I shorted the idle switch connections and the oscillation is there, unplugging the idle switch, it goes away but idles high. What did you find?
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