Idle speed problems

CELICA, COROLLA, ECHO, MATRIX, RAV4 & TACOMA
Idle speed is controlled by Engine Control Module (ECM) and is not adjustable. Check idle speed with engine at normal operating temperature, transmission/transaxle in Neutral, parking brake applied, air cleaner and all air intake hoses installed, all vacuum hoses installed, electronic fuel injection system wiring connectors properly installed, ignition timing properly set, electric cooling fan off (if equipped), and A/C and all accessories off.
Start engine and warm engine to normal operating temperature. Shut engine off. Connect Toyota hand-held tester or scan tool to data link connector No. 3 at driver's side of instrument panel. See Fig. 75, Fig. 76, Fig. 86 and Fig. 87. Hand-held tester or scan tool is used to read engine RPM.
Apply parking brake. Place transmission/transaxle in Neutral. Start engine and maintain engine at 2500 RPM for 90 seconds and then allow engine to idle while noting idle speed. Ensure idle speed is within specification. See IDLE SPEED SPECIFICATIONS table. Shut engine off. Remove hand-held tester or scan tool.
If idle speed is not within specification, check Idle Air Control (IAC) valve, wiring and Engine Control Module (ECM), and air intake system. See IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4-CYLINDER article.

Corolla
NOTE:Idle Air Control (IAC) valve is also referred to as Idle Speed Control (ISC) valve.

For Idle Air Control (IAC) system testing procedures, see Fig. 438.
Fig. 438: Inspecting Idle Speed Control Valve (Corolla & Matrix)

Best thing to do is to remove the idle air control valve and clean the TB port, if it is very dirty, clean the entire TB (remove it). Use carb cleaner/degreaser, then a final spray of brake clean.

You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.

Should be a problem with the IAC. Check to see if it is stuck in the closed position. When starting from cold, the engine idling speed should increase.

Do you mean vehicle is equipped with carburettor? If yes and you have a manual choke, then you need to use it when engine is cold. A cold engine would need to run at a higher idling speed and with a richer mixture.

When engine gets older and the weather gets colder, there would be a difference. When choke is pulled, does the engine idling increases? Have you checkd if the choke is opening correctly?
When was the last time a tune-up was performed?

When choke cable is pulled, the idling speed should increase as the throttle plat would be opened. Check if the adjustment for the choke is correct.