First check for a vacuum leak. Any small loose hoses in the engine compartment? If not, suspect the idle air control valve. I have pasted test procedures for the iac below. Be careful not to confuse the tps with the iac. The tps is centered on the ybro5ttle body. The iac is more on the perimeter. An additional test I do after checking the valve is to plug it back in while it is still off the throttle body and verify that it actuates a little when the key is turned on. It should back up a tad to allow idle air through the passage for starting.
Disengage the IAC electrical connector.Using an ohmmeter, measure the resistance between IAC terminals A and B. Next measure the resistance between terminals C and D.Verify that the resistance between both sets of IAC terminals is 20-80 ohms. If the resistance is not as specified, the IAC may be faulty.Measure the resistance between IAC terminals B and C. Next measure the resistance between terminals A and D.Verify that the resistance between both sets of IAC terminals is infinite. If the resistance is not infinite, the IAC may be faulty.Also, with a small mirror, inspect IAC air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.
Fig. Fig. 2: Using an ohmmeter, backprobe terminals of the TPS sensor to check for proper resistances
Fig. Fig. 3: The TP sensor and IAC sensor are usually located at the side of the throttle body
Fig. Fig. 4: Idle Air Control (IAC) valve wiring and terminal identification
REMOVAL & INSTALLATION
Disconnect the negative battery cable.Disengage the electrical connection.Remove the IAC valve. On thread-mounted units, use 1 1 / 4 in. (32mm) wrench and on flange-mounted units, remove the screw assemblies.Remove the IAC valve gasket or O-ring and discard it.To install:
Clean the old gasket material from the surface of the throttle body assembly on the thread mounted valve. On the flange-mounted valve clean the surface to ensure proper O-ring sealingInstall the valve with a new gasket or O-ring. Tighten the thread mounted assembly 13 ft. lbs. (18 Nm) and tighten the flange mounted attaching screws to 28 inch. lbs. (3 Nm).Engage the electrical connector to the IAC valve.Connect the negative battery cable.