2.3L ('83-'97) 97 ranger starts for 3sec then dies UNLESS gas pedal is pressed

[Auro4ba]

Hey guys, I’m getting a little frustrated because I’m trying to help out a friend and I’m doing much more than anticipated... The truck is a 1997 Ranger with a 2.3L M/t 2wd. My problem is this. I began by throwing a P0340 (cam position sensor) and P0102I (MAF). That being said, I can start the truck just fine every time, then it will immediately stall. It will run smooth as long as I hold my foot on the gas. That is what puzzles me. After reading this if you have any ideas please let me know.
What I’ve done
Motorcraft plugs, wires, PCV, fuel filter, air filter, ignition coils, cam sensor (and required it due to exposed wire) serpentine belt, removed and cleaned MAF with MAF cleaner, and IACV with throttle body cleaner, as well as the throttle body.
If now only throws a P0102 and no longer a P0340. When I started it would run a bit rough while I pressed the gas and now having fixed the cam sensor issue it runs smooth. The problem still exists with the truck shutting off as soon as I take my foot off the gas pedal. Any ideas?

 

[RonD]

Unplug the MAF and see if that helps, but I doubt its related to the stalling, but maybe

All gasoline engines need to be CHOKED on cold start, or they will stall unless "given more gas", or air
In fuel injected engines the computer runs the Choke, because with no Jets a choke plate won't work
Computer uses the ECT(engine coolant temp) sensor to calculate the amount of Choke needed based on temp
Choke means RICH fuel mix and HIGH idle
So on cold start idle RPMs should be 1,100+ depending on outside temp, the colder it is the higher the idle and the richer the mix

So on cold start is idle set at 1,100(high, if no tach), and try to warm it up for 5min, to see if after it warms up it idles lower and stays running
If no high idle on start up, and it idles OK, no stalling after warm up, the I would replace ECT sensor on speculation

MAF and TPS(throttle sensor) are linked for testing purposes
Computer KNOWS its running a 2.3 LITER engine so it KNOWS exactly how much air should be coming in at ANY RPM and any throttle position, its literally just math
The MAF sensor is there to measure the WEIGHT of the in coming air, which changes alot when its cold or warm, and when driving at sea level or at 5,000ft elevation(i.e. Denver)
And computer can estimate air weight using its IAT(intake air temp) sensor
Then based on throttle position it can "test" if MAFs reported "air weight" is high or low, i.e. does it's data make sense

But before you replace the MAF you need to test the TPS, because computer is using that as the baseline for MAF "sanity"

 

[Auro4ba]

Unplug the MAF and see if that helps, but I doubt its related to the stalling, but maybe

All gasoline engines need to be CHOKED on cold start, or they will stall unless "given more gas", or air
In fuel injected engines the computer runs the Choke, because with no Jets a choke plate won't work
Computer uses the ECT(engine coolant temp) sensor to calculate the amount of Choke needed based on temp
Choke means RICH fuel mix and HIGH idle
So on cold start idle RPMs should be 1,100+ depending on outside temp, the colder it is the higher the idle and the richer the mix

So on cold start is idle set at 1,100(high, if no tach), and try to warm it up for 5min, to see if after it warms up it idles lower and stays running
If no high idle on start up, and it idles OK, no stalling after warm up, the I would replace ECT sensor on speculation

MAF and TPS(throttle sensor) are linked for testing purposes
Computer KNOWS its running a 2.3 LITER engine so it KNOWS exactly how much air should be coming in at ANY RPM and any throttle position, its literally just math
The MAF sensor is there to measure the WEIGHT of the in coming air, which changes alot when its cold or warm, and when driving at sea level or at 5,000ft elevation(i.e. Denver)
And computer can estimate air weight using its IAT(intake air temp) sensor
Then based on throttle position it can "test" if MAFs reported "air weight" is high or low, i.e. does it's data make sense

But before you replace the MAF you need to test the TPS, because computer is using that as the baseline for MAF "sanity"

Thank you! I’m going to look into it with in the next several days, so I’ll keep you informed/updated on my progress/status. Thank you so much for the advice

 

[tomw]

I may have missed it, but if you do not get a 'high' idle on cold start, over 1000 rpm, the IAC may not be doing its job. It should bump the idle speed as noted for a cold engine, and also manage idle rpm for loads such as the A/C compressor and power steering pump. Most engines are set such that the throttle plate is so close to being absolutely shut that they will not idle without the IAC being functional. That prevents run-on when the engine is turned off.
tom

 

[Auro4ba]

Tom, thanks for the reply. As far as having an idle over 1,000 rpm, no. The truck will start without hesitation but immediately die as if the fuel is shut off. I’ve cleaned the IACV and there was no change. I’ll check resistance on the iacv when I get back to the truck and update

 

[RonD]

Yes, the Computer uses the IAC Valve to set idle, but its based on engine temp
With key on the computer boots up and opens the IAC Valve all the way for start up, warm or cold engine

So engine should surge above 1,500rpms on start up regardless, on any start up(if you don't touch the gas pedal)
Computer then closes the IAC Valve, to set "target idle", target idle is based on Engine temp, ECT sensor data
If ECT shows temp under 160degF then computer also sets Choke based on that temp, so target idle will be based on that temp, i.e. 1,100rpms

Computer does monitor ETC sensor over time, if ECT is showing 70degF then after 3 to 5 minutes of running its still at 70degF computer will set an ECT trouble code, its not showing higher temp
BUT.........if ECT is showing 180degF all the time, computer just thinks its a Warm restart, computer doesn't "know" how long its been off, 1 minute or 1 month
So no code and NO CHOKE, so cold engine stalls until its actually at 180degF, well above 140degF or so

Failing IAC Valve could cause similar symptoms but computer can monitor RPMs which it uses to set IAC Valve to get target RPMs, so would most likely set an IAC Valve trouble code if computer can't get IAC Valve to set "target idle" RPMs

You can pull the IAC Valve off and plug in its 2 wire connector
Turn key ON
While looking inside at the Valve unplug the 2 wire connector
You should see the valve close, it only moves 3/8" so its not a big movement
Then plug it back in
Should open all the way(for start up, key on)
Repeat a few times

 

[tomw]

If this system has the remote mounted 'thick film ignition', my understanding is that there is a START circuit along with a RUN circuit internally. START provides hotter voltage to the coil, and RUN a lower voltage. The start and run for a few seconds could be a failing TFI where the RUN circuit no longer functions. I have no idea if that would cause an OBD-II code.
I would use a timing light connected to display sparkage... and monitor during cranking and as the engine starts to determine if sparking is going away immediately.
tom

 

[Auro4ba]

Thanks for everything, gents! Finally got it figured out... MAF and IACV somehow went bad simultaneously?! I went back today to check the fuel pressure which was weighing normal range, I had fuel from the rail to the injectors so that was a plus. After cleaning and allowing the MAF and IACV to dry out they were reinstalled with ZERO change and STILL the CEL was on. I’m not one to throw parts at a problem but I threw my hands up on this one and went for it... replaced the MAF and the IACV with inexpensive Autozone parts and she fired right up and ran smooth. That’s all I needed. It’s out of my hair and I can get back to normal life. Haha thank you very much for everything

 

[RonD]

Well that's an odd one for sure

Thanks for the update