2.9L engine stalls

[RonD]

Does it idle at 1,100RPMs when cold, high idle?
And then drop down bit by bit as it warms up, no need to touch the throttle, there is no "idle cam" or idle screw on fuel injected engines

That high idle cold and lower idle warm is done by the computer using the temp sensor and IAC Valve


Why does it accelerate OK, don't know?
Maybe your MAP sensor is going out?

Troubleshooting an engine issue is tough
Heck even troubleshooting a FLAT TIRE is not that easy............
"Put air in it"
"Hey it went flat AGAIN, YOU are NO HELP"
LOL

 

[dend]

Thanks for the feedback Ron. I will check closer tomorrow, but prior to checking the base timing I started the truck and checked timing with the spout connector in place. The truck started with a high idle and high advance. Not sure of the rpms, but I’m guessing probably in the 1100 range. It ran like that for hardly a minute and then slowed to normal idle. It was then that I noticed the slight skip/miss. It ran like that until warm and I pulled the spout connector and checked base timing. At that point I put the connector connector back in place and a neighbor walked over. I attempted to show him how the engine was stalling by manually working the throttle under the hood. To my surprise the engine rev’d perfectly without stalling or hesitation. I then got in the truck and attempted to move it. That’s when it started the hesitation, stalling and erratic rpm swings. It behaved like that even when I put it back in park. The rpms were varying and the engine cut off. At that point I gave up for the night.

 

[RonD]

It reads like Temp sensor is OK, as is IAC Valve

You have a MAP sensor that reads vacuum level in intake, this is the LOAD sensor for your year
Its usually mounted on the firewall, has a vacuum hose and 3 wire connector, its not big, maybe 2" square
Find it, check the vacuum hose for cracks/leaks
Unplug the connector and check for corrosion and plug it back in

Unplugging and plugging back in connectors CLEANS the contacts, this is often why a new sensor fixes a problem, it wasn't a bad sensor it was a dirty connection

Do the same with Throttle sensor(TPS), unplug it and check for corrosion and plug it back in

TPS and MAP sensor work together to determine engine LOAD
Computer uses LOAD to determine best air/fuel mix and then best spark timing to ignite that mix

When you REV an engine in the driveway there is minimal LOAD
When you REV in gear, LOAD goes up so air/fuel mix needs to get richer and spark timing needs to change for the richer mix

On older distributors there was Vacuum Advance, this was the LOAD "sensor", that adjusted spark timing for engine LOAD
Yours has the computer calculating spark advance, still using Vacuum, but from the MAP sensor and throttle position

 

[dend]

Thanks for explaining. It’s really helpful. Initially the truck would not idle. It would start and the soon after the rpms would fluctuate and the engine would die. I found an article about the MAP. I tested the MAP and found it to be defective. I replaced it with a BWD MAP, and now the engine no longer dies. As I mentioned it still hesitates under load, but doesn’t die with just idling. I did unplug the TPS and used a needle inserted into the TPS to read the voltage while slowly increasing the throttle. The voltage increased like it is supposed to and didn’t seem to have flat spots. I’ll work with computers and I know what you mean about dirty connectors. Could the TPS be corroded in the inside causing the issue that I can’t see with a simple voltmeter test. I’ll disconnect the TPS and MAP connectors tonight and clean them with contact cleaner to see if that helps. Thanks again Ron.

 

[RonD]

Then you may want to pull the computer and have a look inside, the older capacitors leaked, which would cause odd issues
They are easy to replace, had to do this to my 1994 a few months back
There were 3 in mine, not sure if 1986 used the same setup, but should be close, they are both EEC-IV model computers