So! my 1990 EB bronco has been surging until hot, idling slow at all times (all lights dim, heater blower slows down, etc. when idling in drive. Slightly better in neutral, but not much.)

I got codes from it. (I used a long piece of cord off a broken laptop power brick, the prongs for the wall socket (not polarized) fit beautifully into the STI connector and the Signal Return pin on the DLC, and the other end (which has bare wires) reaches into the cab, allowing me to connect or disconnect the two from the driver's seat)

I got the following codes (descriptions from Ford Fuel Injection » 2 Digit Self-test Codes 11-32):
KOEO:

• 11: System pass!

CM:

• 34: PFE or EVP circuit has intermittently failed above the closed limit of 0.67 volts.
• 87: Voltage was not detected on Fuel Pump Monitor while the engine was running.

KOER #1 (didn't cycle OD lockout switch):

• 44: Thermactor Air Injection system inoperative (Right side).
• 65: Overdrive OFF switch was not cycled during KOER test (user error).

KOER #2 (cycled OD lockout switch):

• 12: Cannot control RPM during ER Self-Test high RPM check.
• 44: Thermactor Air Injection system inoperative (Right side).

The Haynes Manual describes these slightly differently.

• 12: RPM unable to reach upper test limit.
• 34: EVP voltage above closed limit.
• 44: Thermactor air system inoperative - right side.
• 65: Overdrive cancel switch open, no change seen.
• 87: Fuel pump primary circuit failure

Interestingly, the slow idle problem seemed to be gone during the KOER tests (though, I never put it in gear)

The fuel pump has operated without any outward sign of trouble since i've had the car, and it only has errors in continuous memory (however, i've had the battery disconnected not too long ago)

I'm not sure what to make of the thermactor errors. The haynes manual doesn't mention how to diagnose them further.

I suppose the next thing i should do is check/replace the EVP sensor, and the fuel pump wiring, but I thought I'd check with you guys first

Does anyone have some insight? what should I check?

 

Lets start at the high end and work down. Code 87 is an interesting find. IF Code 87 is indeed accurate the truck should not run at all. Since you were able to perform the KOER test (twice) I'd suggest that this codes was captured in memory at some time in the past and is no longer an issue. However, double check that the resistance in the circuit between pin 22 of the ECA and the fuel pump relay does not exceed 5 ohms. If it does clean connections or replace the wiring. (I will note that the need for this last procedure is extremely unlikely).

Code 65 you obviously figured out.

Code 44 along with 34 is your most likely culprit for idle control issues. With that said, Code 44 indicates that the Thermactor system wasn't doing anything during the test. The simple things to look for first are broken, loose hoses between the smog pump, the diverter valve (behind the passenger side cylinder head), the crossover tube (between the back of the cylinder heads) and both check valves in the system (One on the crossover tube and the other in the down tube to the catalytic converter). Loose or broken vacuum lines between the TAB and TAD solenoids (mounted behind the ignition coil on the driver's side) and the diverter and EGR valve are also cause for this Code to rear its ugly head. If all of this "plumbing" is in tact there is a rather tedious process for testing the TAB and TAD solenoids that I can walk you through. But check for the easy fixes first.

Code 34 is probably one of the most common fault codes that comes back. It merely indicates that there was too much voltage sent back to the ECA from the EVP (EGR Valve Position) sensor during the KOER test. The most likely cause is a bad sensor but you can check/clean the EVR filter (small foam filter that resides between the EVP sensor and the top of the EGR valve). And although it should not cause the EVP sensor to run beyond its normal travel, an EGR valve that is stuck wide open could also cause this Code to trigger.

Code 12 is another OE. RPM's failed to reach upper limit. During the KOER a single CEL flash prompts the test administrator to perform the "goose" portion of the test which basically means that you have 10 seconds for the throttle to be snapped open so that the engine rpm reaches 2000. As soon as the target 2000 rpm is reached release the throttle. Code 12 will not appear if this is done at the proper time.

And the Code everyone prays for and wishes were the ONLY one they ever saw.. Code 11 indicates all is well and the system needs nothing.

 

Most of that jives with how I understand things.

On code 87, i thought it must be a resolved issue (it showed only in memory), except that recently I had the battery out (checking whether my dad's Suburban's battery was bad by using my known good battery in his truck)

Doesn't that mean it's a recent code?

I was pleased with myself for figuring out 65, insignificant as it is.

As for 44, i'll have to do those checks before I can move further on that.

34 didn't show up during KOER (or KOEO, only in the Continuous Memory), so i'm guessing I shouldn't worry much about it now. Then again, the memory was reset recently, so it's not a terribly stale code.

For 12, i had guessed that it was OE, except that I hadn't seen it on both tests, and I stepped on it when prompted both times. I guess i'm not as consistent as the computer would like.

I certainly wish I saw more 11's during my tests, though I suppose that all in all there's not much rong with this truck.

I'll let you know what I find.

 

Well, there's a new idling issue, and a new code
Code 53: TPS circuit has intermittently failed above maximum 4.5 volts.

I did some checks on the sensor with my multimeter, which didn't reveal anything out of place. What should I be checking next?

Oh, and the new issue is that the truck will almost stall, and then hold the RPMs at ~2000 for a bit, idle normally for a moment, and then repeat once or twice