2002 Ranger low idle

[Daniel Black]

I picked up an '02 Edge 4x4 cheap to try and make some money on. The previous owner had a new trans installed then this problem started a couple months later so he got disgusted and parked it. It sat since May 2019. I had to replace the fuel pump to get it started so I drained the gas and changed the fuel filter. My fear was a timing problem but luckily the motor sounds good. No rattles or knocking of any kind. Hit the key and it fires right up and idles smooth as glass. The problem is it only idles at 400-500 rpm. When you put it in gear it dies. if you touch the gas pedal it dies. All it will do is idle. I checked the basics. Fuel pressure is dead on. All the sensors and wires are plugged up. I pulled the throttle body and IAC for cleaning and that made no difference. I sprayed either around but cant find any obvious sign of a vacuum leak. Since the battery was out for 3 years it hasn't run enough to trip any codes. Anyone ran into an issue like this with a 4.0 SOHC? I really don't know what to look at next

 

[gaz]

Daniel Black,

Does this Ranger have an automatic transmission?

 

[Daniel Black]

Yes, it's an automatic.

 

[RonD]

No, not a common issue on 4.0l SOHC

On cold start any fuel injected engine should idle at 1,000-1,200rpm depending on how cold it is outside
This is Choke Mode, all gasoline engines need to be choked on cold start, this means high idle and rich fuel mix

Choke mode is done by the computer, based on ECT(engine coolant temp) sensor and IAC Valve to set idle
It is part of Open Loop, and Choke mode is used until coolant(ECT) is above 140degF, idle will slowly come down during that time

When coolant is above 140degF, idle should about 750rpm for automatic and go to 800rpm if trans is put into gear or AC is on
Manual trans would have 650-700rpm warm idle and bump up 50rpm with AC on

Air is how gasoline engine RPMs are controlled, more air = higher rpm, more fuel = flooded engine, lol
So an air leak would cause higher rpm, a vacuum leak

If RPMs do not go high on cold start then IAC Valve is not working or computer is not working
Unplug 2 wire connector on IAC valve, turn on the key, test voltage by putting meter probes on the two wires
Should see about 11volts, computer is opening IAC Valve all the way for startup, engine running voltage is about 7volts

If you have the correct voltage(11v) at the IAC Valve then I would suspect IAC Valve is the issue
You can only replace it with Motorcraft or Hitachi brand IAC Valves
Or hit a wrecking yard to get a stock model, its not a common failure, so fairly safe bet used