86’ 2.9L help needed!!!

[Jaycejohnson1998]

Howdy, first time posting here, I’m Jayce.
I daily a 1986 Eddie Bauer bronco 2 with 85k miles and I love it but this 2.9 is perplexing me.

The engine starts only if you floor it as you turn the key and quickly let off the throttle. I’ve replaced the computer as my stock one wasn’t outputting trouble codes even after recapping the board. $108 dollars later it starts betterish and I busted my test light walking to the truck to check codes.

It starts much better when cold but even then you still have to floor it and let off. It runs super rich for around 10 seconds then smooths out but will not idle down lower than 1100rpm even with the screw backed all the way out. I’ve read and read through the many 2.9 threads on here and I can’t find anyone with the exact same set of issues. I’m almost scared to pick up a new test light and find out that the harness isn’t any good when it never even blinks haha. I’d appreciate it if anyone who had experienced the same stuff could lend a guiding hand,
Thanks!

 

[franklin2]

The test plugs lay under the hood open to the elements for years. You usually have to take a knife or something and scrape the contacts in the two plugs to get them to work so you can read codes.

Unplug the idle air control valve wiring after the engine is warmed up and see if it idles down. If it doesn't, and you still have the idle stop screw backed all the way out, then air is coming in from somewhere it shouldn't be. If air is getting in the engine will keep running. It should stall with the idle air control valve unplugged and the idle stop screw backed out.

If unplugging the idle air valve plug made it stall out, I would take the idle air control valve off (2 bolts) and see if it's all gunked up in the valve and in the passageways to the valve. Clean it out with carb cleaner if it is, and also take the large rubber air intake hose off and take carb cleaner and clean around the throttle blade. Open the throttle with your hand and clean all around and behind the throttle blade.

 

[Jaycejohnson1998]

The test plugs lay under the hood open to the elements for years. You usually have to take a knife or something and scrape the contacts in the two plugs to get them to work so you can read codes.

Unplug the idle air control valve wiring after the engine is warmed up and see if it idles down. If it doesn't, and you still have the idle stop screw backed all the way out, then air is coming in from somewhere it shouldn't be. If air is getting in the engine will keep running. It should stall with the idle air control valve unplugged and the idle stop screw backed out.

If unplugging the idle air valve plug made it stall out, I would take the idle air control valve off (2 bolts) and see if it's all gunked up in the valve and in the passageways to the valve. Clean it out with carb cleaner if it is, and also take the large rubber air intake hose off and take carb cleaner and clean around the throttle blade. Open the throttle with your hand and clean all around and behind the throttle blade.

I’ve had it off a few months ago to clean it and it looked super. Clean but I didn’t think to try unplugging it. I’ll try that after I clock out and let you know if that works thank you!

 

[Jaycejohnson1998]

The test plugs lay under the hood open to the elements for years. You usually have to take a knife or something and scrape the contacts in the two plugs to get them to work so you can read codes.

Unplug the idle air control valve wiring after the engine is warmed up and see if it idles down. If it doesn't, and you still have the idle stop screw backed all the way out, then air is coming in from somewhere it shouldn't be. If air is getting in the engine will keep running. It should stall with the idle air control valve unplugged and the idle stop screw backed out.

If unplugging the idle air valve plug made it stall out, I would take the idle air control valve off (2 bolts) and see if it's all gunked up in the valve and in the passageways to the valve. Clean it out with carb cleaner if it is, and also take the large rubber air intake hose off and take carb cleaner and clean around the throttle blade. Open the throttle with your hand and clean all around and behind the throttle blade.

Unplugged it and it stalled out instantly. Passageways and hose appear clean still

 

[Hoosierman]

I know it's not the most relatable example, but I'll just say this anyway.

My 1993 Jeep ZJ died on my a few months ago and when. Finally replaced the battery AND the starter (yes they both conked out on my the same instance...), the vehicle wouldn't start unless I pressed all the way down on the pedal, and it wouldn't idle at all after that. So it turns out the IAC also conked on me at the same time as well.

I don't know exactly how the Ranger and BII are different to that experience, but at least it's something to go by.

 

[rusty ol ranger]

I would put the screw back where it needs to be. That screw isnt really supposed to be fooled with unless setting idle speed. Which shouldnt really need to be done on EFI, but there is a procedure in the 2.9L forum on a sticky post.

That said, i would try to get some codes from it, and check the voltage coming out of the TPS

 

[Jaycejohnson1998]

I would put the screw back where it needs to be. That screw isnt really supposed to be fooled with unless setting idle speed. Which shouldnt really need to be done on EFI, but there is a procedure in the 2.9L forum on a sticky post.

That said, i would try to get some codes from it, and check the voltage coming out of the TPS

What voltage should I see with the tps

 

[franklin2]

What voltage should I see with the tps

Stay below 1 volt. It will vary depending on where you set the screw, but it needs to be below 1 v when the throttle is closed.

Since it stalled, that means you do not have an air leak. To set the screw where it belongs, get the engine warmed up fully. Unplug the idle air control valve plug again, and set the screw so the engine idles 500-600 rpm. Then plug the idle air control valve back in.

If everything is correct, the idle still will not be right till you drive and start and stop it at least 3 times. It has to "learn" the new settings. If you still have the very high idle after driving it for awhile, something else is wrong. I suppose you know a high idle is normal for the first 5 minutes or so after a cold start.

 

[Jaycejohnson1998]

Stay below 1 volt. It will vary depending on where you set the screw, but it needs to be below 1 v when the throttle is closed.

Since it stalled, that means you do not have an air leak. To set the screw where it belongs, get the engine warmed up fully. Unplug the idle air control valve plug again, and set the screw so the engine idles 500-600 rpm. Then plug the idle air control valve back in.

If everything is correct, the idle still will not be right till you drive and start and stop it at least 3 times. It has to "learn" the new settings. If you still have the very high idle after driving it for awhile, something else is wrong. I suppose you know a high idle is normal for the first 5 minutes or so after a cold start.

Yeah I’m aware it should idle high for a bit but the lowest it regularly goes is 1100. I once hit a bump really hard and at the next red light it tried to idle down lower for a bit but it went back up quickly

 

[franklin2]

Once you get the throttle set, if you still have a high idle after driving it, one thing that could cause that would be the coolant temp sensor is not working correctly. When you get to that point, there are some resistance readings you can take on that sensor at different temperatures. If the computer thinks the engine is cold, it will make it idle high.

 

[gaz]

@Jaycejohnson1998
If your coolant temp sensor is determined to be good/functioning correct, look at all your vacuum lines; even if you replace all of them as a preventative measure (maybe $30), on a 38 year old chassis...money well spent, plus you've ruled out a vacuum leak...for years to come!!