I'm hoping someone can help me out. My 91 SR5 has very low idle when cold. It will shut off if I let go of the gas pedal. It accelerates well with no misfires or pre detonation. I did a head gasket change a while back and valve shims were adjusted. But it existed even before then. I changed the fuel filter around four years ago but my suspicion lies with fuel pressure. It's fuel injected with a chrome exhaust header, cold air intake. There are no vacum leaks and it turns on very good. Once it's warm it's fine for the rest of the day. The car is garaged kept and I've had it since new. Does anyone else have any thoughts?
I beleive there is a valve attached to the intake manifold that should have coolant flwing through it. this valve is supposed to allow extra air past the throttle plate during warm-up to allow for a fast idle. this valve is probably stuck closed or carboned up.
- water temp sensor, telling the ECU the engines warm when its not...
- IAC idle air control valve, usually on the bottom of the throtle body under a white plastic looking block with i think 3 wires.... Basically take off the throtle body and take it apart and clean it out with throtle body cleaner and a old tooth brush, don't use carb cleaner it will most likely ruin rubber parts...
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Ah when she was in her glory, Not so nice anymore 358k 17years old her time is getting short ....
I agree with the ignition system, but in addition to that it could be the fuel injectors...if they cant flow the needed fuel your car wont idle right...have you realized any loss in power?
but then he'd have problems when the engine is warm as well. when the engine is cold things contract, a tiny crack in the distributor cap might close up when the engine bay is warm. or once the combustion chambers warm up the weak spark due to bad plug wires might be enough to light off the air/fuel mix better.
but i think the 1st place he should go is the IAC valve, it lets a small amount of air bypass the throttle plate when its closed to keep the engine running.
I've worked on the IAC valve all day yesterday and found it to be clean. It has cylinder in it which has fine threads for adjustment. I made my own socket to make quick adjustments but when it's cold, the idle is now either too high or too low & I can't get it to work right. Now I don't know if I screwed it up more. I've worked on cars for a while and the Haynes manual doesn't mention nothing about this valve. You guys are gurus on this stuff. Can someone elaborate a little more how this valve works? I can probably figure something out. Once I have an understanding on how it works and what it supposed to do, I'm kinda good on trouble shooting. I'm getting somewhere thanks to you
by the way new plugs and real toyota replacement parts only in my baby. I really appreciate the feedback.... I'm like you guys.... not a underhood duct tape mechanic in anyway
the IAC is duty cycled by the PCM, the PCM at 0% percent throttle has a minimum desired engine rpm it wants to maintain. it will duty cycle the IAC valve to maintain that rpm as best it can.
mechanically its a pintle valve actuated by a solenoid. the solenoid pulls the pintle to and from its seat to allow more or less air past depending on what the PCM is commanding.
The Auxiliary Air Valve, located on the underside of the throttlebody, provides additional intake air around the throttle valve when the engine is cold. This raises the engine idle speed until the engine can idle normally on its own. The Air Valve has a thermo wax sensor that stays in contact with engine coolant and blocks off the bypass air passage as coolant temperature rises to normal operating temperature.
This is not electronic. Remove the valve, make sure you can blow air through it cold.
Last edited by 91gtssilvertop; 11-18-2006 at 07:09 PM.
The Auxiliary Air Valve, located on the underside of the throttlebody, provides additional intake air around the throttle valve when the engine is cold. This raises the engine idle speed until the engine can idle normally on its own. The Air Valve has a thermo wax sensor that stays in contact with engine coolant and blocks off the bypass air passage as coolant temperature rises to normal operating temperature.
This is not electronic. Remove the valve, make sure you can blow air through it cold.
It turns out that an automatic transmission throttlebody and the manual tranny throttle body are slightly different. My car is manual and the throttle position sensor part #'s differ. I used an automatic throttle body for a while because it came off a wrecked car with only 16k miles. They looked the same but 40k miles later I'm putting my old throttle body back on.....problem is solved. Thanks to all for your input.
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Low idle when cold on my 4AFE
Linear Mode
