New member with idle issues

[MBC1980]

Hey guys, my dad has a 1986 F150 5.0 4x4 that he ordered in Sept of 1985. It was the first EFI 4x4 off the line in Norfolk Va. Since it was new it has always had an issue with cutting off, especially on cold start. When it idles high, it will drop down and sometime stall or it will catch and stay running. Put in gear and it will stall typically. It is notorious for cutting off and not staying running and it has had that issue since it was new. No one could ever figure it out.
A while back it developed a skip in the idle. When taking off and climbing hills it runs good but in overdrive or sitting idle it has a skip and that affects how the transmission downshifts and it shutters when slowing down. When accelerating even mildly its smoother and the skip goes away.  
So far here's some things that have been done recently.
Intake and valve cover gaskets
Idle air control valve
Thermostat
PCV valve
Throttle position sensor
MAP sensor
Fuel pressure regulator
Swapped out a computer from junk yard
Harmonic balancer
New belts and hoses
Spark plugs and wires
02 sensor
Fuel relay
Oil sending unit
Water pump
Fuel filter is relatively new
Solenoid
Starter

Motor was rebuilt 20 years ago and has low miles on it since rebuilt.
No vacuum leaks
Fuel pressure is good
Not sure about compression

The temp gauge stays very low and oil pressures reads very high.

It has been garage kept and never been a daily driver. We've had a specialist from a Ford dealership look at it and cant figure it out. Was this a common issue with this new EFI system at the time?
Thanks in advance for any help that could be provided.

[Gary Lewis]

Welcome, Micah!  I'm sure glad you joined 'cause the others on here are much more likely to know about the EFI systems then I do.

Beautiful truck as well.

But here's a suggestion - copy and paste your entire post into a new thread in the main section.  You may get more help there than here in the NMSH section as more people are likely to see it.

So, where's home?  We have a map (Bullnose Forum/Member's Map in the menu) and we could add you to that if we had a zip code or city.

[MBC1980]

Ok great thanks!

On Mon, Dec 7, 2020, 10:08 AM Gary Lewis [via Bullnose Enthusiasts Forum] <[hidden email]> wrote:

Welcome, Micah!  I'm sure glad you joined 'cause the others on here are much more likely to know about the EFI systems then I do.

Beautiful truck as well.

But here's a suggestion - copy and paste your entire post into a new thread in the main section.  You may get more help there than here in the NMSH section as more people are likely to see it.

So, where's home?  We have a map (Bullnose Forum/Member's Map in the menu) and we could add you to that if we had a zip code or city.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI

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[Gary Lewis]

By the way, I see you are posting via email.  You can do that but it isn't advised as it brings a lot of baggage with it, as shown in the screenshot below.  I've circled the "baggage" that gets copied in unless you take pains to delete it before responding.

Instead of responding to the email, if you'd click the link in the email that's below the line that says "If you reply to this email, your message will be added to the discussion below:" you'll be taken to the forum and you can post there/here.  And doing so won't bring with it the baggage.

But that's your call.  However, it is more difficult to read posts if you do reply w/the baggage and not everyone will bother to do so and you won't get the responses you would otherwise.

[kramttocs]

Welcome! Very, very nice truck

[ArdWrknTrk]

Welcome to the forum Micah!  
Gorgeous truck.

One thing that was common, caused stalling especially off the line, was failure of the Thick Film Ignition system.
So much that Ford was forced to replace them in tens of millions of vehicles after a few deaths and class action suits.

The factory placed the module on the distributor, using it as a heatsink.
What's usually done to remedy that is to relocate it to the drivers side inner fender with a dedicated heatsink.
FatFoxx and McCauley Racing both have kits available.

This MAY be your issue.
Accurate diagnosis is the first step.

[MBC1980]

Thanks!

[Gary Lewis]

MBC1980 wrote

Thanks!

Well done!  See how clean that post is?  

[MBC1980]

The only time the stalling happens is if its sitting and idling or sometimes but less than common is when slowing down to make a turn when not accelerating but never when driving.

[MBC1980]

Yes thanks for the info. I didnt realize I was replying to a thread when I saw the email response.

[old55pete]

There was a recall on the IAC valve that pretty much the same symptoms as what you are talking about. To find out for sure if that recall has been done, there should be an emishion recall sticker on the header panel in front of the radiator.

Another thing I found out was that the grounds needed to be cleaned up. There is a ground connection in the stock ground cable between the batterie and the engine block. It attaches to the frame by the right engine mount. If it is not hooked up, it will cause something similar. There is also a ground cable that goes from a stud on the firewall by the wiper motor to a stud on the lower, left side, by the inside rear corner of the valve cover. The stud is one of the lower intake manifold mounting bolts. If ether end is dirty, it will cause similar problems.

In your shotgun list of parts replacement, I dident see that the TFI module had been changed. Has the TFI module been changed in the last few years? They have a bad habit of failing with similar symptoms also. The strange thing about the TFI is that it will over heat and fail and once it cools off it will work again

[grumpin]

Welcome!

[ArdWrknTrk]

It really does sound like an IAC.. or the TPS.

Micah, did you ohm those components once you installed them?

[MBC1980]

No but I can check that out. What reading should I get?

[ArdWrknTrk]

I forgot exactly where the TPS voltage should be.
It's value is probably in the EVTM troubleshooting section.
Bill Vose is a wiz with these things. (He should be, having run a tune-up  shop for years)

Two things I keep forgetting about the 5.0 is that the IAC has a diode to help isolate it and that they have a knock sensor.
If you have a timing light you might try seeing what is happening when the truck struggles or dies when cold.

You might also try locking the timing to see if the truck has a steady idle and keeps running without the ECM meddling.

Have you measured the fuel pressure or checked for contamination in the vacuum line after the regulator?

[old55pete]

With the ignition on, engine not running. The voltage at the TPS needs to be 1 volt. Keep in mind that the TPS has NO adjustment.

[MBC1980]

I didnt check the line after the regulator but will do that and will check the grounds to the engine. Fuel pressure is good.

[ArdWrknTrk]

If the regulator is holding 40 you should be good.
I just go through all these quick checks in my mind as I think of how to quickly eliminate possibilities.

[MBC1980]

I replaced the tfi module today and also the coolant temp sensor. The sensor was corroded and broke on half. Also had a bad wire on the coil. All fixed but no luck on fixing the skip and surging.

[MBC1980]

My grounds were on tight but are corroded. Would this affect idle and surging?