Air-Line ControllerFixing an idle control valve
Here's the symptom: When you start your mid-'90s or newer Toyota 4-cylinder car, the engine starts okay, but the idle speed is extremely low. You might even have to keep your foot on the accelerator pedal for a minute or so, just to keep it from stalling. The check engine M.I.L. is not illuminated and, when the engine warms up, all seems to be normal, or at least a bit better. Perhaps the idle compensation function-a noticeable idle speed boost when the transmission is put into "D" or "R," or the A/C is turned on-is not spot-on either, but the cold-running problem is getting really irritating. For a relatively quick fix, here's the lowdown on the low-down idle for this common Toyota engine and many others similar to it.
Even back in the early days of fuel injection, there was some form of idle control. Manufacturers used to employ a separate system for cold-idle compensation, often not controlled by the computer. They also used separate, electrically actuated valves for A/C and other engine-load compensation. These were often not controlled by the computer either. Hot, unloaded idle was adjusted with a screwdriver.
This system worked well, but manufacturers wanted to simplify things and cut production costs. The idle-control systems on most late-model passenger cars, including the Toyota engine shown here, utilize just one control valve, which is operated exclusively by the computer.
The valve function is similar to a washerless faucet-the difference being that air flow rather than water is the medium that is controlled. Essentially, the valve controls the size of an intake vacuum leak. The bigger the "leak," the more idle compensation is available. There are no adjustments to be made. This system controls all idle functions-hot and cold, loaded and unloaded. It works as well, if not better, than the old system-but is pretty intolerable to live with when wounded.
When symptoms like the ones noted above occur, the culprit is usually the valve itself. Specifically, the valve won't let the desired amount of bypass air into the intake, so the resulting idle compensation will be insufficient. Since no adjustments are feasible, and disconnecting the valve and attempting idle compensation by changing the throttle angle will lead to even less tolerable symptoms, the valve must be removed for inspection.
Unless tangible debris is jamming the valve, cleaning will generally do it no good, and it will have to be replaced. Other manufacturers have made these valves more accessible, some less, but replacement is not beyond the skills of a decently equipped do-it-yourselfer.
On the Toyota engine, the valve is visible without the need to remove anything. In order to actually replace it, though, the intake air-pipe and coupler WILL have to be removed for access. Exercise care when working on the attached hoses and pipes, as the rubber and plastic don't take kindly to force.
It's best to attempt the replacement procedure with a cold engine, as there are coolant hoses connected to the valve. These provide a flow of warm coolant to the valve to keep it from freezing in low temp/high humidity conditions.
The trickiest part of the operation is removing the four Phillips-head pan screws, which attach the valve to the throttle body. Note the need for a "stubby" Phillips screwdriver, and a ratchet with a bit and extension, which will greatly assist you in accessing and removing these screws. You won't have an absolutely straight shot at all four screws, so be patient and careful. You may otherwise strip the drive on the screw head (what an annoying development that would be!).
Make sure to replace the sealing O-ring with a new one, and make sure it's properly seated before installing the valve. Otherwise you may end up with a coolant leak at the valve. Then, just button it up in the reverse order of removal, and you're there. When you next start the engine, the idle should go up to approximately 1500 rpm, and gradually decrease shortly thereafter. Mission accomplished.
The valve may be a bit pricey, but at least you've saved some dough on labor. And YOU won't have to be the air-line controller anymore during warm-ups.
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