Working my way through fault codes, need help

This is my first troubleshooting post for my 1986 XLT Lariat 2WD with 302 EFI/AOD. The problem I'm having is a high idle when I first start it (higher than normal cold idle) and then as it warms up the idle drops but is still higher than normal and it will momentarily drop and then go back to high idle. It does this repeatedly every 10 seconds or so. It also sounds rough, not very smooth.  I verified the timing is at 10° BTDC with the spout connector disconnected but when it is connected it varies from 18-20° while idling. I pulled codes and I got CM codes of 22, 63, 31 and KOER codes of 41 and 13. It passed the KOEO self test. The book says to focus on the KOER codes first. I would think that code 13 (RPM at idle out of range/low) might be caused by code 41 (HO2S sensor low/system lean). I should also mention that I have a ticking sound when the engine is cold but it goes away as it warms up. I think it might be an exhaust manifold leak. What do you think? If that is the case, can that be causing an O2 sensor problem? I also plan to check my TPS based on the code 63 to make sure it's within specs.

Should I focus on the O2 sensor first or could an exhaust manifold leak be causing the problem? Anything else I should be looking at? Hopefully I can clear up the KOER codes and then see if any of the CM codes come back.

The first thing that comes to mind is the tps. I have had times where ohming out the tps did not find the ghost in the machine. Voltage test also. Swapping in a new one and setting it to .85 volt at signal return is the best suggestion i can give. Over time they can corrode and give erroneous signals to the ecm. And keep in mind the ecm reads very minor changes and reacts.

I have learned to do the first code first and it may clear later codes, so you are correct in doing 41 first.

I am going to reply directly to this one. We went through this with my son's 1986 F150 4WD, 302 EFI and AOD. He had idle issues and chattering EGR solenoids. The 1985/86 truck EFI system is different from the later ones in the idle setting procedure. The TPS has no adjustment other than the idle stop screw and is set to a voltage reading.

First and very important, to check the "sweep" on a potentiometer correctly you need an analog meter as digital ones do not continuously update and you are looking for a smooth change. Second, idle on these is set to a voltage reading, 1.0 +/- 0.1 if I remember correctly. This can be done (and should be) engine off, key on. These systems do run the idle up on cold start, but should drop back shortly after starting.

One of the reasons for setting the throttle (not idle speed) by voltage is the way the system works, the EGR comes in based on TPS voltage at a very low change so if the voltage is too high you get chattering EGR solenoids and a surging idle.

The wiring on these first generation EFI systems can be a problem, I have seen harnesses with bare wires, crumbling insulation and really poor grounds. Good luck with it.

Thanks Bill, I have ordered an analog meter. It should be here tomorrow. What do you think about my code 41 "running lean"? I will check the O2 sensor (as soon as I find it). Does it sound like I have an exhaust manifold leak? Could that be why I am running lean? I assume the TPS and the running lean are 2 separate issues.

Assume nothing! Lean condition could be as simple as a clogged fuel filter. These are large canister , water separator type that are in constant circulation to help keep condensation in check. Yes water clogs them!
Also it could be that the fuel injectors are not 100% . Even one or two could do it.

All true but I am trying to address the fault codes first before I move on to other things. I have a specific code for a lean condition so I might as well start there.

Yes keep it simple. Start with routine maintenance items before moving on to mech failures. Fuel filter, vacuum lines etc. could cause a lean cond. especially if you dont know the full maint. history of the truck or if it sat for a long time. Old trucks dont do well sitting too long

Your O2 sensor should be on the rear of the right exhaust manifold, one wire style. Be careful removing it, they love to strip the manifold.

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)

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.

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.

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

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

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.