2000 2.5L idles fine, stalls when cold at stop sign/light

[G-Man]

My 2000 Ranger 2.5L 5-speed with 206K miles starts up fine, idles great but when I drive away and get to the first stop sign/light, it dies. If I let the truck warm up six minutes or longer, no problems when I get to a stop sign/light. Once the truck has warmed up, it runs great, no more stalling issues. Truck has new plugs, new spark wires, we've checked the fuel pressure and it's good. We are getting no check engine light so we can't look at a certain area by checking the code from the OBD II reader. Any ideas of where else to look, ICV???

G-Man

 

[tomw]

Does the engine idle fast when first started cold? It should idle over 1,000 rpm for the first few minutes. If not, either the IAC is not controlling the idle higher when requested(cold, A/C, power steering load), or the computer thinks the engine is warmer than it is. Normally the computer will bump the cold idle speed, but if the coolant temp sensor and/or the incoming air temp sensor lies, the idle may not be bumped.
The two sensors vary resistance based on coolant and air temperature, and can be measured and compared to known good. The IAC can be removed from its location on the throttle body(most) and cleaned to see if the idle speed can be affected. It may or may not last if cleaned.
tom

 

[RonD]

+1 ^^^

IAC Valve or ECT sensor will be the problem

Change ECT sensor first, easy to do and not an expensive part
Start cold engine and idle should now be 1,000+ RPMs

If it is still low Clean IAC Valve, read here: http://www.explorerforum.com/forums/index.php?threads/iac-valve-cleaning-thread-w-pics.84220/

Before cleaning but after unbolting it, plug in its 2 wires
Turn key ON/engine off
IAC Valve should be all the way open
Unplug the wires, it should close all the way
Plug wires back in, and it should open all the way
Repeat as you see fit to make sure it is working/moving
If not replace it

If it is moving then clean it


Heads up on ECT sensor, there is also an ECT(engine coolant temp) SENDER, used for dash board temp gauge
They look alike on top but are not the same, and not interchangeable parts

 

[G-Man]

We've checked both the ECT Sensor (replaced it) and IAC valve and neither was the cause for why my Ranger dies at stoplights/stop signs when cold. Any other suggestions on where to look? I'm at a loss on this issue.

G-Man

 

[tomw]

Check on the underside of the upper intake manifold to be sure the large-ish vacuum lines are tight, and unbroken.
Check the ACT - Air charge temp sensor - mounted in the upper intake for proper ohms at a given temp. There's a table with proper values, and you can put it in the freezer to check that the ohms change when it chills.
There may be a 'stove' around the exhaust manifold that is used when the engine is cold. A bi-metal valve that closes cold will apply vacuum to the diaphragm that makes engine air come from around the exhaust, so it is warmed a bit. That should prevent icing and help atomization when cold. Do you have a small hose going around the back side of the cylinder head to the bottom of the intake? It may be tee'd into the heater core line to supply some heat to the intake and also help fuel:air mixing. Check that the hose is flowing(getting hot) and is adding heat if equipped.
tom