Odd start problem

[naford]

On Tuesday morning I go to start the truck. 02 Ranger 4.0 FX4. It turns over but won't start. I apply gas and it runs but I have to keep it at around 3000 rpm to keep it running. I start to left off the gas slowly and finally the rpm jumps up and the truck can hold an idle. It seems to run fine without any power problems. At the end of the day I throw the computer on to see if there are any hidden codes. Nothing. Well it starts on Wednesday morning and runs woithout a problem. Tonight I go out and I have to apply gas to start the truck but this time it doesn't take that long to be able to hold an idle. Again it seems to run ok. The only thing I notice is that the idle seems a little low. Has anybody seen this?

 

[Andy D]

damp wires, old plugs? Loose connection? A load of bad gas?

 

[70roadrunner]

throttle position sensor?

 

[LearjetMinako]

Idle Air Control solenoid might be starting to go bad.

 

[Earl43P]

Idle Air Control solenoid might be starting to go bad.

+1, clean the IAC.

 

[RonD]

IAC(idle air control) valve is easy to check.
With engine warmed up and idling unplug electrical connection on the IAC, idle should drop to 500rpm or below and maybe stall, if idle doesn't drop then IAC is stuck, remove and clean.

IAC valve is a controlled "vacuum leak", if you were to pull off the vacuum line at the power brake booster and put your thumb over the end your thumb would be "the IAC valve", as you slide your thumb off the end the idle would go up, the more air you let in the higher the idle, the less air the lower the idle.
All Fuel injected engines use an IAC valve, it is not a "ford thing".

On startup, without touching the gas pedal, the engine idle should go up to 1,500+ RPMs
Then idle should drop to 1,000 RPMs on a cold engine or 750 RPMs on a warm engine
That is the computer testing the IAC valve, it opens it all the way then checks the ECT sensor(see below) and closes IAC valve to correct RPM for engine temp.


The ECT(engine coolant temp) sensor tells the computer the coolant temp of the engine.
It is a 2 wire sensor and looks similar to the 1 wire sender used for the dash board gauge.
Since you have an OBDII scanner you should be able to call up the ECT sensor reading when engine is cold.
If this sensor was showing a warm engine, then computer would think it was a restart not a cold start, so engine would be running too lean and IAC wouldn't open as much to set cold idle.
ECT sensors rarely fail, but not never fail

Could also be water in the gas tank, bad gas.
Water is heavier than gas, so will settle to the bottom of the tank when vehicle sits for a few hours.
Fuel pump pick up tube is at the bottom of the tank...................
There are additives that help remove the water in the tank.

 

[Majagit]

There is a small metal wire guide just in front. I bent it to keep in place. No more problems.