Well IAC(idle air control) valve would have been my first choice as well.
Computer uses IAC valve and CKP(crank position) sensor to set idle, 1,000rpm cold and 750rpm warm
Those are presets in the computer.
All Fuel injected engines also use an ECT(engine coolant temp) sensor to get cold or warm data, this is a two wire sensor only used by the computer, dash board temp gauge uses a one wire sender.
ECT sensors rarely have a problem and I doubt it would cause the issues you describe.
Just to confirm IAC, CKP, ECT and computer are all on the same "page" the following should happen on cold start.
Foot off the gas pedal
RPMs should go up above 1,200
Then drop down to approx. 1,000rpm
That's the computer opening the IAC valve all the way for startup, so high RPM
Then lowering RPM to "cold idle" based on ECT temp.
As engine warms up idle should start dropping until warm engine idle is 750rpm, closer to 800 on some automatics.
If all this happens the computer and mentioned sensors are all working as they should.
With engine warmed up unplug IAC valve, idle should drop down to approx. 500rpm
If engine stalls there should be a screw on the throttle linkage that will set the "no IAC" idle, this is there to prevent stalling in case IAC fails, adjust it so warm engine will idle at 500-600rpms with IAC unplugged, but not above 600rpms
The engine could be flooding out when cold, dirty injectors can cause this also older spark plugs.
Can of Seafoam in the gas tank will clean injectors, some motorcraft spark plugs will get back strong spark.
Fuel injected engines also have a routine to clear flooded engine.
Turn key to RUN
Push gas pedal to the floor and hold it there, if engine isn't running this tells computer to shut off injectors.
Crank engine, if it starts to fire then yes you were flooded out, since injectors are off it shouldn't fire at all.
Besides dirty injectors, a faulty fuel pressure regulator(FPR) can cause flooding, FPR is on the fuel rail and has a vacuum line attached, remove this vacuum line and check it for gas or gas smell, if gas is detected replace FPR.
The diaphragm in the FPR can crack and gas is then sucked into the engine via the vacuum line.
During warm up the only fuel/air mix determination the computer has is the MAF, the O2 sensors can't be used until engine warms up.
Cleaning is good but you should probably test it with volt and ohm meter.
TPS(throttle position sensor) failing probably wouldn't give you those issue, but they are easy to test with volt meter and a couple of sewing pins.
Computer sends TPS 5 volts, if throttle is closed TPS sends computer under 1volt, if throttle is wide open TPS sends computer over 4.5volts.
So it works just like a volume control or light dimmer, turn it one way for more the other way for less.
TPS will have a 5v wire and a Ground wire, 3rd wire is the voltage that is sent back to computer.
Pierce wires with pins, far enough apart so they can't short to each other, then turn on key and test voltages while opening and closing throttle, you want to see nice smooth changes, if you see any jumping up and down replace TPS.
Last edited by RonD; 01-21-2014 at 10:21 PM.