rough hot idle

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Old 10 Feb 2006, 03:34 pm   #1 (permalink)
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Default rough hot idle

The engine of my 96 Camry (4 cyl, manual, 118k miles) lopes at idle when
the engine is very hot.
Typical situation; after 45 minutes or more of highway driving I get off
the road, or slow way down for traffic, and the engines idle drops off
almost to a stall and then goes back to 8-900 rpm. RPM keeps going up and
down as if it wants to quit. (It has quit.) Playing with the gas peddle
keeps it going. This doesn't happen (so far) in local driving, even though
the temp guage reads the same.
From a quick and dirty check I'd say the air filter looks ok, so do the
vac lines and the air duct to the throttle body.
Does anyone have any trouble shooting suggestions?

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Old 10 Feb 2006, 08:31 pm   #2 (permalink)
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Default Re: rough hot idle

Pressing the acelerator keeps it going then it's probably your idle
control valve. Typical problem with Toyota.

Do a search on for ways to clean this thing. Remove the valve, clean it
with sensor-safe throttle body cleaner without getting the solvant into
the electrical side. Turn the valve to clean all areas. Should keep you
going for another year or two before it plugs up again.

Does anyone know if Toyota ever solved this problem?

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Old 11 Feb 2006, 10:34 am   #3 (permalink)
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Default Re: rough hot idle

Excuse me for pointing this out but "peddle" is something "peddlers" do
- like door to door salesmen. The thing you press to make the car go is
a pedal.
Your engine idle is controlled by an idle air control valve at the
bottom of the throttle body. On one end is a bimetallic thermostatic
coil and on the other end is an electromagnetic coil controlled by the
ECM (engine computer).
There is no lubrication for the cylinder in the IAC that moves to
progressively reveal a larger opening for air flow at idle, so the
valves can stick.
Sounds like the computer is trying to tell your car how to idle, but
the valve is responding erratically.
Try this:
Remove the clamp on the large air hose at the throttle body next time
the idle is acting up.
Spray some TriFlow into the rectangular opening right in front at the
bottom of the throttle body. This is the air intake for the idle
control valve. When the throttle is fully closed at idle, that valve
lets measured amounts of air pass by to control idle speed.
TriFlow contains Teflon and is usually available at bicycle stores, and
possibly home improvement and motorcycle shops also.
I discovered this after completely dismantling, cleaning and adjusting
the throttle body, and replacing the IAC valve with new factory fresh,
only to have the problem return.
The Teflon fortified lubricant seems to have enough residual
effectiveness to have resolved the problem now.

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Old 10 Jan 2007, 01:22 pm   #4 (permalink)
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Default Re: rough hot idle

The answer turns out to be the EGR valve in this case. I have found that it
sticks (open) after running the car for an hour or so at highway speeds.
Using the gas pedal keeps it from dying. If it dies then on restarting it
won't idle unless I give it gas. Rapping the top of the EGR valve unsticks
it (once or twice I heard the valve snap closed). Everything is fine until
the next highway trip.

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