Working my way through fault codes, need help

[mat in tn]

I just wanted to update on my progress. I checked for vacuum leaks using carb cleaner but did not find anything. I checked the TPS and it tested good. I also cleaned up some grounds and added a couple including a new negative battery cable to the engine block and frame. I attempted to tighten the exhaust manifold bolts to see if I could fix the exhaust leak but that did not go well. Rusted bolts and studs and I definitely don't want to break one so that is a project for another day. Next I focused on the O2 sensor. It tested bad so I replaced it. The idle sounded better but it still wasn't quite right. Too high and still surging a little bit. The previous owner must have adjusted the idle screw. I ended up backing it out 4 full turns and that seemed to allow the ECM to adjust the idle on it's own. I cleared the codes, took it for a drive and then checked the codes again. All codes are clear and the idle is much better! Now on to other issues.

A question: is there an adjustment procedure for the idle screw for the 5.0L EFI? I have read that you are not supposed to touch it, but once it is out of adjustment how do you reset it? Or should I just leave it since it seems to be idling good (not sure what the RPMs are but it sounds pretty close to right).

well the method i use is to connect a digital meter to the tps output and at idle in run or running there is a signal voltage from the tps to the ecu which tells the ecu when you move the throttle and how much. that voltage spec is .5 to 1 volt at idle. i set them at .9 volt. you make the adjustments with 8mm-/5/16 throttle position screw (the one the sticker says not to turn)

[Sparky]

well the method i use is to connect a digital meter to the tps output and at idle in run or running there is a signal voltage from the tps to the ecu which tells the ecu when you move the throttle and how much. that voltage spec is .5 to 1 volt at idle. i set them at .9 volt. you make the adjustments with 8mm-/5/16 throttle position screw (the one the sticker says not to turn)

I'm not sure we are talking about the same thing. I mean the screw that provides a mechanical stop to the rotating part of the throttle assembly. My TPS is not adjustable like the later years.

[mat in tn]

I'm not sure we are talking about the same thing. I mean the screw that provides a mechanical stop to the rotating part of the throttle assembly. My TPS is not adjustable like the later years.

let me do a little more study. but the one i am referring to has the tps on the bottom of the throttle body directly opposite the throttle linkage at the top and is operated by a blade on the bottom end of the throttle blade pivot shaft. therefore, the screw on the top acting as a throttle stop is actually the tps adjuster. every efi throttle body ,i have on the shelf whether 5.0 or 5.8 is that way.

[vjsimone]

I'm not sure we are talking about the same thing. I mean the screw that provides a mechanical stop to the rotating part of the throttle assembly. My TPS is not adjustable like the later years.

My 2 cent....

I believe the Throttle Stop Screw from the factory was adjusted so that the throttle plate was completely closed, but not jammed against the Throttle Body inner wall.

As a baseline you could back that screw off until it is not touching the stop, then bring the screw back snug against the stop, but not opening the throttle.

Or (insert a 0.025 inch feeler gauge in-between the Stop screw tip and the throttle stop, the feeler gauge should fit snug and be able to slide in and out with slight difficulty.)

Measure your TPS voltage, to see where you are as a base line.

If you had the Throttle body off, in a perfect world, you would not see any light through it. But sometimes they get deformed over time.

I can’t remember for sure, but I thought the original 85/86 EFI had slots in the TPS for adjustment. I think I remember getting replacement TPSs and obliging the mounting holes to allow for a small adjustment.

If you use the Idle Stop Screw to adjust the voltage higher, you could be introducing unaccounted for additional air intake, which could cause a higher than normal idle like a vacuum leak does. But a small adjustment may not make any difference in the idle.

So, all that said, this was an old procedure I have used in the past.

5.0L V8: 1985 Truck and Van; To adjust idle stop screw:

 

1. Disconnect the battery for 3 minutes to erase the current idle control program from ECA memory.

Turn the throttle stop screw in (clockwise) 1 turn.

2. Reconnect the battery, start the engine, and run it at 1800 rpm for 30 seconds.

3. Place the transmission in drive and let idle speed stabilize.

4. Back out the throttle stop screw until idle speed is 600 ±20 (AT).

Then back out the screw another 1/2 turn.

5. Stop the engine and disconnect the battery for at least 3 minutes. ??? to erase the current idle control program from ECA memory. ???

6. To check curb idle speed, start the engine and run it at 1800 rpm for 30 seconds. Place the transmission in drive and let idle speed stabilize.

 

[mat in tn]

My 2 cent....

I believe the Throttle Stop Screw from the factory was adjusted so that the throttle plate was completely closed, but not jammed against the Throttle Body inner wall.

As a baseline you could back that screw off until it is not touching the stop, then bring the screw back snug against the stop, but not opening the throttle.

Or (insert a 0.025 inch feeler gauge in-between the Stop screw tip and the throttle stop, the feeler gauge should fit snug and be able to slide in and out with slight difficulty.)

Measure your TPS voltage, to see where you are as a base line.

If you had the Throttle body off, in a perfect world, you would not see any light through it. But sometimes they get deformed over time.

I can’t remember for sure, but I thought the original 85/86 EFI had slots in the TPS for adjustment. I think I remember getting replacement TPSs and obliging the mounting holes to allow for a small adjustment.

If you use the Idle Stop Screw to adjust the voltage higher, you could be introducing unaccounted for additional air intake, which could cause a higher than normal idle like a vacuum leak does. But a small adjustment may not make any difference in the idle.

So, all that said, this was an old procedure I have used in the past.

5.0L V8: 1985 Truck and Van; To adjust idle stop screw:

 

1. Disconnect the battery for 3 minutes to erase the current idle control program from ECA memory.

Turn the throttle stop screw in (clockwise) 1 turn.

2. Reconnect the battery, start the engine, and run it at 1800 rpm for 30 seconds.

3. Place the transmission in drive and let idle speed stabilize.

4. Back out the throttle stop screw until idle speed is 600 ±20 (AT).

Then back out the screw another 1/2 turn.

5. Stop the engine and disconnect the battery for at least 3 minutes. ??? to erase the current idle control program from ECA memory. ???

6. To check curb idle speed, start the engine and run it at 1800 rpm for 30 seconds. Place the transmission in drive and let idle speed stabilize.

very true! adjusting the throttle stop screw changes the available idle air initially, the iac tunes in from there but we are only talking about a small amount. the extremes would be if the throttle is too open for the iac to manage yet the tps tells the ecu "no demand" then it labels it a vacuum leak. so, a little goes a long way when fine tuning these.

[Sparky]

My 2 cent....

I believe the Throttle Stop Screw from the factory was adjusted so that the throttle plate was completely closed, but not jammed against the Throttle Body inner wall.

As a baseline you could back that screw off until it is not touching the stop, then bring the screw back snug against the stop, but not opening the throttle.

Or (insert a 0.025 inch feeler gauge in-between the Stop screw tip and the throttle stop, the feeler gauge should fit snug and be able to slide in and out with slight difficulty.)

Measure your TPS voltage, to see where you are as a base line.

If you had the Throttle body off, in a perfect world, you would not see any light through it. But sometimes they get deformed over time.

I can’t remember for sure, but I thought the original 85/86 EFI had slots in the TPS for adjustment. I think I remember getting replacement TPSs and obliging the mounting holes to allow for a small adjustment.

If you use the Idle Stop Screw to adjust the voltage higher, you could be introducing unaccounted for additional air intake, which could cause a higher than normal idle like a vacuum leak does. But a small adjustment may not make any difference in the idle.

So, all that said, this was an old procedure I have used in the past.

5.0L V8: 1985 Truck and Van; To adjust idle stop screw:

 

1. Disconnect the battery for 3 minutes to erase the current idle control program from ECA memory.

Turn the throttle stop screw in (clockwise) 1 turn.

2. Reconnect the battery, start the engine, and run it at 1800 rpm for 30 seconds.

3. Place the transmission in drive and let idle speed stabilize.

4. Back out the throttle stop screw until idle speed is 600 ±20 (AT).

Then back out the screw another 1/2 turn.

5. Stop the engine and disconnect the battery for at least 3 minutes. ??? to erase the current idle control program from ECA memory. ???

6. To check curb idle speed, start the engine and run it at 1800 rpm for 30 seconds. Place the transmission in drive and let idle speed stabilize.

vjsimone, I believe your procedure is correct. I found this in a Ford manual online:

The problem is, I don't have a tach at the moment so I can't set the idle speed. Since it is close I will live with it for now and set it properly when I get a tach gauge for the dashboard. Thanks for everyone's help with these issues

[Sparky]

very true! adjusting the throttle stop screw changes the available idle air initially, the iac tunes in from there but we are only talking about a small amount. the extremes would be if the throttle is too open for the iac to manage yet the tps tells the ecu "no demand" then it labels it a vacuum leak. so, a little goes a long way when fine tuning these.

mat in tn, I found some more info on the TPS. It sounds like you can adjust them if you elongate the screw holes so you can rotate it a bit more. I believe the voltage at idle should be right around 1.0v

[mat in tn]

mat in tn, I found some more info on the TPS. It sounds like you can adjust them if you elongate the screw holes so you can rotate it a bit more. I believe the voltage at idle should be right around 1.0v

elongating the holes does work. and a chainsaw file is the cleanest and safest way i have found to do it. at 1.0v the tps is "hair trigger" at the ready yes. Perfect with a new iac and perfectly clean throttle body. im use to old stuff

[vjsimone]

vjsimone, I believe your procedure is correct. I found this in a Ford manual online:

Screenshot_20211214-125909_Drive.jpg

The problem is, I don't have a tach at the moment so I can't set the idle speed. Since it is close I will live with it for now and set it properly when I get a tach gauge for the dashboard. Thanks for everyone's help with these issues

Yes, I recognize that document. I tried to find it the other night, no joy, but I did find my simplified version I was using locally. It is a challenge to hold that idle @ 1800rpm. Following that procedure was easier with 2 people. I forgot about the 30 second limit to adjust. We were aware of it during our efforts, but I should put that back in my modified version. Good luck.

[vjsimone]

Yes, I recognize that document. I tried to find it the other night, no joy, but I did find my simplified version I was using locally. It is a challenge to hold that idle @ 1800rpm. Following that procedure was easier with 2 people. I forgot about the 30 second limit to adjust. We were aware of it during our efforts, but I should put that back in my modified version. Good luck.

Another thing to look for is to see if your throttle plates have drilled holes in them. Some do, some don’t. Some have plugs in the holes. I believe these holes were used to adjust the idle air intake volume. Plugging them may lower your idle if needed.