Hello all,
I have a 1986 f150 4x4 with a 302 efi with an AOD auto trans. When i start it up, it goes to high idle, everything normal. When it kicks off of high idle, the idle starts surging from 400 to 1200rpm. Sometimes the idle surges so low that it dies. After a while, it then stops surging and idles niceley until you put it in gear. The engine then surges up to roughly 1300 rpms, and then goes back to the normal in gear idle. Sometimes at stoplights it will start hunting. I have noticed that if i unplug the wiring from the idle air controller, it wont hunt, but it idles super low (400 rpms). I replaced the iac and the throttle body doesn't seem dirty. Could anyone help? Vacuum leak? Throttle position sensor? Any help is apreciated.
Thank you,
Trei

 

Did you check the passageway through the manifold from the IAC?

I have a related problem with my 86 efi. When you start it up for the first time of the day it'll surge and die. Start it the second time and it's fine. Never really had enough to go on to fix it but it may be related.

 

check this out:
https://www.ford-trucks.com/forums/1...lso-fs-ft.html

 

Search this forum for a long series of posts by Archion. He went through a similar issue with his 86.

 

I looked, but i cant find the thread. Could you maybe give me a link to it?
Thank you so much.

Trei

 

Try this. https://www.ford-trucks.com/forums/9...g-a-demon.html
It ended up finally being the aftermarket TPS he had installed. It would not come down to 1.0 volts at closed throttle. His EGR vacuum valve would open then the vent solenoid would start chattering. Disconnecting the EGR position sensor would stop it for a short time. We chased it for almost a year. He had my breakout box and several test instruments all that time.

 

Rusty,
I have an 86 302 EFI also and have been through the entire ignition and fuel injection realm of issues.

Follow these steps:

1. Pull off IAC connector....Does the truck still run? If so your idle set screw is adjusted improperly.
2. If Idle set screw is adjusted improperly your IAC cannot function properly. The IAC is what controls the idle, not the idle set screw. So, start the truck, turn up the idle with the set screw, then unplug the IAC. The truck should still be running. Now, slowly back the idle set screw out until the engine just dies. Pull the battery cables and let it sit for awhile to reset things. After awhile, maybe 30 minutes or so hook everything back up and start the truck.
3. Does the truck idle better? If so problem may be solved. If not, you need to check your timing to eliminate that. Pull your SPOUT connector and hook up your test light. If running a stock ignition system make sure your timing is set to 10 deg BTDC. Plug the spout back in and take it for a drive. Your computer may need to relearn some things.
4. Still have a problem? Check for vacuum leaks.
5. No vacuum leaks? Still surging? Have your TFI module tested to rule out that its bad or good.
6. TFI module good? Try swapping MAP sensors.
7. New MAP sensor didn't fix it? Your fuc&$%. lol Just kidding. Double check your O2 sensor, knock sensor, harness wires....etc.

I have tried to put some of the easier things first. My guess is that your idle set screw has been tampered with and you need to reset it properly as I mentioned above.

 

Thank you all soo much. I will reset the idle. If that fails, i will continue to work on it.
Thanks
Trei

 

Let us know how it works out!

 

Good afternoon all. My first post and will attempt to make it coherent.

1986 Ford F-150 XLT Lariat 302 EFI AOD

Very recently after running fine for the past 18 months, when starting from cold, stumbles and idles rough and will quit. Starts right back up every time. I wrap up the RPMs until it's warm and it runs better.

When warm at operating temperature, runs fine will idle with an occasional surge, then when driving at highway speeds, starves and slows down, RPMs pick back up with plenty of power, slows down again, picks back up. Happens sporadically. May run fine for 50 miles without incident. Once warm, does not die. Keeps running.

Background: 2012 - Both Low Pressure tank pumps replaced, main high pressure pump replaced. Fuel filter is new, tanks switch works fine.

Last week, replaced TCM, Distributor and module, plugs, wires, distributor cap, rotor button, IAC, EGR, Fuel Pressure Regulator, TPS. . I run a bottle of Techron cleaner through the fuel tanks every third tank fill.

Continues to exhibit same symptoms and behaves as if it's starving for fuel, intermittently. Now that we know what's NOT causing the problem any suggestions would be very much appreciated. Thank you.

 

Have you run through properly setting the TPS as described above?

I had a similar issue with my 86 302 and it ended up being the fuel pressure regulator.

 

Yes, and all parts replaced are OEM quality. MAP sensor also replaced. Can't find a vacuum leak anywhere. Plenum gasket is solid. I'm starting to think it's cursed.

 

You cannot eliminate the possibility that one of your replacement parts are no good. Test your TPS at idle. Voltage will be between .8-1.0 volts. Attach a voltmeter across the green wire and black wire. Black neg, green is the signal wire to the computer. Tell us what you get.

p.s. you will have to pull back the wire insulation a little and tape it up with electrical tape when you are done.

 

I completely agree. I find 1 of every 4 new parts has defects. I did test the TPS, EGR, MAP Sensor, IAC and all fit within optimal operating ranges. Main fuel pump tests at 35 lbs of pressure, both tank pumps are working, timing is set at 10 BTDC, yep, had to tape up exposed wires after test. I'm thinking TCM MAY be problem. The original part number is one vowel different than the "Factory Replacement" module I bought and installed. Ford tells me the new part number is fine. I have driven the truck long enough after each addition to allow the computer to "learn". Thanks for your reply Ray.

 

OEM Quality in the case of these early EFI engines isn't always good enough, Archion chased a demon on his 86 until he finally broke down and bought a Motorcraft TPS. The correct procedure for setting the throttle stop on the 85-86 EFI is different from a lot of the newer ones.

On these, with the key on, and using a good digital multimeter, measure the voltage between the dark green with light green stripe wire on the TPS and the black with white stripe wire. With the throttle closed it needs to 1 +/- .05 volts. If it gets over 1.10 volts, it turns on the EGR vacuum valve, when this happens the ECM picks up the EGR movement and starts pulsing the EGR vent valve in an attempt to regulate it, this makes the engine start to miss, IAC opens to correct it, vacuum changes and next thing you have is a wildly surging idle in or out of gear.

One clue, the set of solenoid valves right behind the battery, one of them will chatter, that is the EGR vent valve.

Due to all the problems with Archion's truck (he's my son), I have a couple of extra 1986 ECMs. Ford changed the number very frequently between 1985 1/2 and 1987. You think maybe there were some problems?