Could be
1 Throttle valve/sticking or leakage
2 air intake system/vacumn system leaks.
3 Idle air control (IAC) valve/idle speed control (ISC) actuator
4 condition of fuel or fuel filter.
5 engine coolant temperature (ECT) sensor
Checks
ensure ign off
unplug IAC muti plug
switch ign on
check voltage between harness multi plug terminal and earth
(IAC) valve check supply voltage
terminals 2 and earth should read battery voltage
check resistance
ensure ign off
disconnect IAC multi plug
check resistance between IAC valve terminals as follows
Terminals Resistance
2&1 9.7ohms approx
2&4 9.7ohms approx
2&3 9.7ohms approx
2&6 9.7 ohms approx
all the same resistance.
To check (ECT) sensor
ensure ign off
disconnect ECT multi plug
releive pressure in cooling system
remove ECT sensor from engine
immerse sensor probe in coolant of specified temperature
check resistance between ECT sensor terminals
ECT temp sensor may be checked in situ if engine temp and resistance readings compared.
Temperature Resistance
0 degree C 5900 ohm
20 degree c 2500 ohm
40 degree c 1180 ohm
60 degree c 600 ohm
80 degree c 330 ohm
chris, December 2005
