88 ranger 2.9v6 idle jumps around badly

[Valleyboy907]

i have an 88 ranger 2.9v6 the idle jumps around like crazy not sure what the problem is maybe injectors? when the truck gets warm it doesn't do it as much.
if anyone has some input on this i would greatly appreciate it
ive replaced the inline fuel pump, pressure regulator, TPS (Throttle Position Sensor) fuel filter, ran tons of fuel treatment threw the tank. im at a loss here someone please help me out here!!

 

[RonD]

On the side of the upper intake is the IAC(idle air control), these are used on fuel injected engines.
It is, in essence, a controlled vacuum leak, there is a valve/piston inside that allows in air, this is controlled by the computer and sets cold high idle and then warm normal idle.
This IAC can be removed and cleaned.

If there is another vacuum leak then IAC will try to respond to set a steady idle this can cause surging in the idle, so check for vacuum leaks, i.e. hard or brittle vacuum lines, you can use a spray cleaner or starting fluid with engine running and see if spraying at a certain area causes a change in RPM denoting a vacuum leak as the spray is sucked into the intake.
A PCV valve can be stuck open, pull it off and shake it or replace it if it's old.

On fuel injected engines a regular choke setup won't work, there are no jets, so they added an ECT(engine coolant temp) sensor, this is a two-wire sensor for the computer, there is a one-wire sender for the dash board temp gauge, they are usually located near each other.
The ECT tells the computer that the engine is cold and computer then runs injectors rich and advances the timing, also sets IAC for higher idle.

If this sensor has failed then cold engine would be harder to start and would run poorly until warmed up.
This sensor can be tested with an OHM meter, test cold and then warmed up, OHMs should change as sensor warms up.


EDIT:

Oops, the 2.9l uses a Speed Density system, so a MAP(flow) sensor and MAT(temp) sensor