I've had my 1986 2.9L ranger for ~3 years and although it does always start, how it starts depends on its current state. When it is cold, it explodes into life on the very first crank and then you must be quick onto feathering the gas to sustain the start. When it is warm, and has only been off for a few minutes, it starts after a couple cranks and you have to feather the gas only a little bit to keep it that way. When it is warm and has been turned off for more than 10-15 minutes, you have to crank for 3-10 seconds while gently feathering the gas and listening for it to murmur a sign that it is starting to fire, then you stop cranking the starter and gently feather the gas until the engine stops sputtering and jumps into life (3-5 seconds). Once it is started and warm, it idles but with a slight rough/shaking of the engine. If it is still cold, you must hold in the clutch pedal to keep it running in idle. I'd appreciate input on what I might do to improve the starting and idle.

 

Welcome to the forum

You understand that with a fuel injected engine there is no "gas" pedal like a carb had, it is now an "air" pedal, when you press it down you are giving the engine more air, no extra fuel comes in, when starting, once engine starts you get both extra air first, then extra fuel, but only above 400rpm.
Pumping the air pedal also doesn't give engine more fuel, carbs had an accelerator pump which did, EFI doesn't

So "feathering the air" and getting a startup could mean engine is flooding out.
MPG gone down a bit recently?

There is a Fuel Pressure Regulator(FPR) on the engine, it has the Fuel Return hose, and a smaller Vacuum line.
Find it and remove that vacuum line, check it for gasoline, should not be any of course, replace FPR if gasoline is found

IAC(idle air control) Valve is on the upper intake by/on throttle body
IAC Valve controls the air for idle and Start Up, when it opens fully engine RPMs can climb to close to 2,000rpm
Remove it, 2 bolts, plug in its 2 wires and turn key on(engine off)
IAC Valve should now be OPEN all the way
Unplug the 2 wires and IAC Valve should close all the way
Plug wires in again, and it should OPEN all the way
Repeat as much as needed to make sure it is working.

You can clean these, read here: How to: - IAC valve cleaning thread (w/pics) | Ford Explorer and Ford Ranger Forums - Serious Explorations

After engine is warmed up, shut it down and pull the large air tube off the intake.
Open throttle and SMELL intake air, should be 0 gasoline smell injectors are off.
If you smell a strong gasoline smell you have a leaking fuel injector, and it is flooding out the engine when its warm, after sitting overnight(cold engine) gasoline would have evaporated and fuel pressure would be 0.
So it would start but struggle to run until fuel pressure built back up.
Should be 30psi engine running then stay above 20psi engine off, for a few MONTHS
"Feathering" the air pedal would help dry out a flooded engine, but try just pressing air pedal down to the floor and cranking, for faster dry out



2.9l engine used TFI spark module, these were known to stop sparking when they got warm, would work fine after cooling a bit.
When you shut off a warm engine ALL the heat from the engine and exhaust manifolds stays in the engine bay, no fan to move the air around and no vehicle movement either.

So parts can get "heat soaked", meaning hotter than they would with engine running.
So TFI module could be a reason for slow start, after 10min, but hasn't had time to get heat soaked after only 3 or 4 minutes


If everything is working as it should with a fuel injected engine it should go like this:
Turn key to start, don't touch gas pedal
Engine starts a REVs up to about 1,500rpm, IAC Valve is open all the way
Then RPMs will start to drop as computer closes IAC Valve from Full OPEN
Computer has "target idles"
Cold engine is usually 1,100
Warm engine 650, automatics are 750
Computer gets engine temp from ECT sensor, this is only used by the computer, temp gauge has separate SENDER.
ECT tells computer what idle RPM to set, engine coolant temp sensor, ECT

ECT sensor is not expensive to replace, but it can be tested with OHM meter and pot of hot water

 

Thanks RonD for the input.

I had recently replaced both the fuel pressure regulator and idle air control valve. However, I never checked whether the IAC valve was actually working; I wasn't sure how to and the book only gave directive on reading out the resistance across the valve terminals. It ends up that no signal was coming to the idle air control valve. I confirmed electrical continuity back to the electronic control module. Luckily, when I bought my rig it came with a bag of parts, including two spare ECMs. I swapped out the ECM, the IAC now gets a signal, and the truck runs completely different. Thanks again for your input! I'm amazed that the rig ran as good as it did without a functioning IAC valve. Later, I will verify your additional advice for the fuel injectors.

 

Good work

Thanks for the update and fix

IAC Valve gets 12volts on 1 wire when key is turned on
The other wire is a Ground that runs back to the computer, the computer Pulses the ground signal on that wire to open IAC Valve a little or alot, same as varying the voltage but uses ground side instead of "+" side