Idle Problem

[filmmaker1225]

'99 RX300, well maintained, new transmission, belts replaced, etc.

Just had the throttle body cleaned but problem persists. Car starts up, but idles low and dies. Needs to be started quite a few times, revved and dropped into gear in order to avoid stalls. Runs verty smootly after that. Runs quietly and efficiently on road. Problem is intermittent.

At first it seemed to only occur when car was already warm, but after cleaning throttle body that seems not to be the case. Problem is unpredictable.

I've heard the words MAV and ECU bantered about. Is it a bad idle control or poor connection to same?

Anybody got a clue?

Thanks

Dan

[riwyle]

You said you had the throttle body cleaned. Did this also include cleaning the idle control valve ports and actuator?

[SKperformance]

you need to clean the IACV

[filmmaker1225]

Thank you both for your responses. I don't know about the idle control valve or the actuator. And I will check to see that the IACFV is cleaned. What exactly is the IACV?

Thanks,

Dan

[riwyle]

When you ask "what is the IACV" I am not sure how much detail you are asking for, but I will try to give you my understanding of what it does. First, the IACV is the idle air control valve. As the name implies, it provides and controls the amount of air needed for idle conditions. It is important to realize that when you "step on the throttle" or "give it some gas" you are only opening a butterfly valve that allows more air into the inlet manifold and then into the cylinders. There are devices that continually measure the quantity of air going to the engine and the signals from these sensors are used by the computer to control the amount of fuel that is injected. This butterfly valve is large enough to admit enough air for maximum engine output, but this makes it impossible to properly control the very small amount of air needed for idle. When this large valve is barely cracked off its seat it is providing too much air. To overcome this control problem, a very small valve termed the IACV is installled to bypass the large valve. Hence at idle, the large valve is held fully closed and all of the air required feeds through this small valve, which easily modulates (controls) small air flows. If you remove the flexible duct after the air filter, you will see the throttle (butterfly) valve with a hole in the bottom of the throttle chamber ahead of it. This hole is the inlet to the IACV which is located direcly beneath. There is another hole downstream of the throttle valve where this idle air is re-injected into the inlet chamber.

I hope this explains why, when the IACV is sticky or stuck closed the engine still runs good at speeds above idle.

It is quite simple to remove and clean this valve and the small ports(holes) which feed it.

[filmmaker1225]

Thanks very much. I don't intend on doing this work, but now, at least I think I understand it better.

The car tends to start well in the morning, (although not always) What usually happens is the idle drops way down. If you repeatedly step on the gas it will eventually rev up to 1200 with a little whoosh, then drop down to about 1000RPM, a little high.

My guess is that something is dirty, maybe the IVAC, since the thruster body was cleaned, at a shop.

Thanks so much!

Dan