I have a 1986 5.0 efi and it has been sitting three years but started monthly for 10 minutes at a time.

Issue is I drove it about ten miles at 30mph at most just to roll it around some thinking about putting it back on the road. Next day go out for another short slow ride and on level or downhill accelerated ok but on incline didn't want go bogged down. Barely touching gas would climb hill slow..

Tried

Changed fuel filter inline
drained old gas
put in 5 gallon of fresh fuel
added sea foam
Bled fuel line to the rail
Checked vacuum lines
Exhaust coming out tail pipe pretty strong (freely)

Issues

Idles with throttle turned up
Press gas bogs out
Press gas very slowly it will accelerate
Now it has small backfire while idling (to much sea foam to 5 gallons gas?)

Please help..

 

You are not supposed to adjust the idle on your 86' EFI 302. The computer controls the idle. If you have been messing with the little screw on the throttle body you have probably messed up.

There are a few components you need to become familiar with.

TPS (Throttle positioning sensor)
IAC (Idle Air Control solenoid)
MAP (Manifold Absolute Pressure sensor)
O2 (Oxygen Sensor)
TFI (I have no clue what it means but its the thingy plugged into your distributor with lots of wires coming out of it)

The TPS is located on the bottom side of the throttle body. The IAC is on the side of the throttle body. The MAP is located on the passenger fender just behind the starter solenoid and has a vacuum line going to the intake manifold and a wire harness connector. O2 sensor is in passenger side exhaust manifold.

Here is what you do to make sure your computer is controlling your truck properly. Start the truck if you can and get it up to operating temperature. With the engine running unplug the IAC solenoid. If your truck continues to run your screw on the throttle body is set in to far. The IAC solenoid should be adjusting your idle. Back the screw out until the engine starts to spit and sputter and just dies. Plug the IAC back in and you should be pretty close on the screw position.

Test your TPS voltage. Peel back a little insulation on the black wire and the green wire. Hook up a voltmeter to these wires (black to neg. green to positive) and see what you get. You should be somewhere between .8 volts to 1.0 volts. Mine runs well at .86 volts. The TPS sensor tells the EGR when to kick in and feeds info to the computer. If its way off then your EGR could be turning on prematurely causing idle issues.

Make sure your MAP sensor has a vacuum line hooked up to the intake manifold.

If you run through all this and still have problems you might take the TFI module out of the distributor and have it tested at Autozone or another parts store. It could be failing.

Still having issues? Check your timing. Check for vacuum leaks. Make sure your plug wires are in sequence. (I had some punk kids re-arrange mine once, that threw me for a loop). Does it still have a catalytic converter installed? It could be plugged up. Check your O2 sensor wire (should be one wire) and make sure its not broken.

Once you run through all this tell us if any of these procedures helps. And report back your TPS voltage.

 

Pull the codes. Pull the codes. Here's how to do it, you just need a testlight. Fuel Injection Technical Library