I don't know where to start

Recently picked up a 1991 Ranger 3.0L 2WD 5 speed. And just replaced the heater core and hoses. I am pretty sure that that has nothing to do with my current problem, but it worked before I did this.
It is hanging around 0 degrees outside. I can start the truck. Let it run for five minutes and then try to drive and move a couple of feet and then the engine dies. Then the engine will crank and won't start (Brand new battery and terminals) If I let it sit for a while I can start it again. But as soon as I try to drive it it dies.

Any idea where to start?

This truck is far from perfect:
Power steering is out
Spedo meter doesn't work
Reverse lights don't work
Gas gauge is screwy (it does however have gas)
Parking break doesn't work


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Normal startup routine for computer control engine is :
Cold engine
Foot off gas pedal
Crank engine
Engine starts and idle should go up to approx. 1,500 rpms
This is the computer opening up the IAC(idle air control) valve all the way for starting.

Idle should then start dropping to approx. 1,000 rpm for cold idle
Computer is closing IAC valve to preset cold idle, based on temperature of engine coolant.
Engine temp is measured by ECT(engine coolant temp) sensor, this is a 2 wire sensor only used by the computer, on the engine there is a 1 wire sender used by the dash board gauge.
Computer is now running in Open Loop(choke mode) and is not using most sensors, it is running injectors rich and slightly advances timing based on ECT temp data.
The MAF(mass air flow) sensor is used to set gross fuel/air mix so an important sensor for lean/rich mix determination.

As ECT sensor warms up computer will drop the idle down to approx. 750 rpm by closing IAC valve more.
Once engine has warmed up computer switches to Closed Loop and uses all the sensors, like the O2 sensors to fine tune fuel/air mix, but MAF is still the main sensor for fuel/air.

If you truck isn't starting up this way then there could be a few problems.

MAF sensor can be cleaned, so can the IAC valve

On the throttle plate(upper intake manifold) there is a sensor called the TPS(throttle position sensor).
It tells the computer when you want to "go" i.e. push down on the gas pedal
If this sensor is unplugged or not working you will stall when trying to "go"
This sensor is easy to test.
Computer sends TPS 5 volts
TPS sends back under 1 volt if your foot is off the gas
TPS sends back over 4.5 volts if your foot is to the floor
So as you press down on the gas pedal voltage going back to computer will go up.
There are 3 wires, one is 5volts, one is ground the other is the voltage going back to computer.
Get a volt meter, set it for 20vDC
get some sewing pins to pierce the wires, need to leave connector attached
Turn on key, leave engine off
Test for the 5 volts and ground, 3rd wire will be the Computer wire, open throttle a bit and make sure voltage goes up in steady increase no sudden jumps, open it all the way then close slowly, should be nice and steady decrease.

Thanks for the quick response. When I test the TPS do I touch the red to the wire and black to a ground?


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Replaced the IAC, cleaned the MAF, and the TPS does as it should when I hooked up the voltmeter. I also put heet injector cleaner in the gas tank.
It has started to loop at idle occasionally (usually when the engine was up). I have checked the vacuum hoses and cannot find a leak. And the PCV has suction.
I was thinking that a new fuel filter might be needed.
Any other ideas if the fuel filter is not the issue?


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Dirty fuel filter shows up first at highway speeds, engine starts to lose power as fuel pressure drops.
But since this is a new vehicle to you and fuel filter is only $10, I would change it just as general maintenance.

You could also have a "ported" vacuum leak.
From throttle plate to intake valves is the "regular vacuum", where most people check for vacuum leaks, and in the past this was generally the only area where a leak would effect performance.

With addition of the MAF sensor and it's location at the air cleaner, a "ported' vacuum leak could effect performance, "ported" vacuum is between throttle plate and air cleaner.
"Ported" vacuum was used on carbs to run vacuum advance for distributors.
In the case of the MAF system any air leak in the long tube from MAF to throttle plate would mean there is more air coming in than the MAF is reporting to computer, so a vacuum leak.