Yo Travis,
Welcome!
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19 @
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
Some basics;
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc. Its a good idea to have a helper read the codes.
Do KOEO test First
Post Code(s) here according to:
KOEO
&
KOER
Look at my Vacuum leak test in post #20 @ vacuum leak test BroncoZone post #20
It shows often overlooked components and hoses such as HVAC System under hood next to evaporator and in cab under dash.
Have a vacuum gauge on-hand first. One of the best low-cost troubleshooting tool around.
...
As Fred suggested;
Throttle Position Sensor Test, Operational Description & Parameters
Source: by Ryan M @
http://www.fuelinjectedford.com/page30.html
Location Diagram & Depiction in 87-91 (from Factory Manual and the Ford Electrical & Vacuum Troubleshooting Manual (EVTM)
Source: by Broncobill78 (Dave) @
http://broncozone.com/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=6665
.
Replacement pics, Source: by xris @
http://www.supermotors.org/clubs/superford/vehicles/registry/detail.php?id=5183&s=29981
"...TO CHECK THE TPS: Turn the ignition to ON (engine not running) and install the probes of the volt-meter into the ground wire (black) and the signal wire (green) on the backside of the electrical connector. This process is called BACKPROBING. Turn your key to the on position (the engine need not be running to perform this test). Your meter should read 0.50-1.0 volts at idle. FYI...because the black probe kept on sliping out of the back of the plug I grounded it to the battery, which works just fine aso.
Rotate the throttle to the full-open position and the sensor should increase voltage to 4.0-5.0 volts. The maximum voltage I got was 1.85 volts. So I was for sure this must be the problem. Many have said that if you do not get a steady increase in voltage, this also is a sign of a bad TPS.
THROTTLE BODY REMOVAL: In most case you will need to remove the TB to get to the TPS. First remove intake hoses and the throttle cable assembly.
The bolts that hold the throttle assembly (located on top of the intake) are 1/2"
Next disconnect IAC plug, coolant hoses and vacuum lines. Remove the four bolts holding the TB to the intake. These bolts are 3/8".
TPS is located @ bottom of the Throttlen Body
While you have this apart...check the intake and TB for crud build-up
Mine was looking pretty nasty. Get some of this, a toothbrush and a rag and start cleaning it out:
CLEAN TB AND INTAKE with carb cleaner.
While I was at it I decided to pick up a NEW Haynes manual. By the time it was all said and done I got the sensor and manual for original price of the sensor...christmas has come early!
INSTALL: Prior to removing the TPS, remove the negative battery cable. Some truck years will require that you scribe a mark across the sensor and the TB to ensure that the new sensor is installed in the same exact location. I was not sure about my truck so I did it anyway.
Remove the two phillips head screws and remove the sensor.
New sensor should be positioned the same as the old...wiring harness pointed away from the IAC.
1) 10th picture (after the spray cleaner) showsd the TB gasket. take it off before you clean the TB.
2) I beleive some models you have to align correctly...not sure if the 86 is for sure but I followed the directions just in case (marking the position)
Engage the tanges of the sensor with the throttle shaft blade, then rotate it clockwise to align the reference marks before installing the screws.
Reinstall the TB in reverse order. Make sure you hook vac lines, coolant lines and sensor wires up..."
****
One guess for now;
Idle Air Bypass aka Idle Air Control (IAC) Valve
Excerpts; "...Go under the hood, and disconnect the electrical connector to the IAB. If the engine begins to stubble or stalls the IAB is functional and does not need to be repaired. If the engine idle does not change you should remove the IAB for inspection.
The IAB can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAB to function properly. Remove the IAB and clean it. There are 2 halves to the IAB, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAB needs to be replaced..." by Ryan M. @
http://www.fuelinjectedford.com/page39.html
.
The IAC valve is used to control engine idle speed & is mounted on the bottom of the throttle body. It allows air to bypass the throttle plate. The amount of air allowed to bypass the throttle plate, will be determined by the EEC IV and will be controlled by a duty cycle signal.
IAC Location pics by Bobby @
.
IAC gasket trim by Nelbur @
http://broncozone.com/topic/22150-fast-idle-problem/?pid=115710
Excerpts; "...Well, my idle hunting problem has been around for about 25 years. Under warranty I would just take the truck back and say, "It's idling like crap. Fix it!" And they would clean everything, and it would be fine for a few months...
After so many years of catching it with the accelerator it is darned hard to leave my foot off it. It is clear to me that by trial and error one can tune the air bypass without the need for the expensive Ford kit. I may combine the two gaskets for more bypass, but the idle is about as fast as I would want now, especially for driving in snow. .."
...
To help identify your transmission, here is the E4OD Overdrive Switch on Dash pic in a 90 by 90broncocanada
http://s137.photobucket.com/user/90bronco_photos/media/repairs%20and%20modifycations/IMG_0001.jpg.html
He had to reattach the6vswith because a previous owner mangled it.
An AOD Automatic transmission doesn't have a seperate OD switch.
AOD have 14 pan bolts, see diagram & pic; P-R-N-(D)-D-1 shifter pattern, note, OD is actually a (D) - Indicator pic by trigger @
.
http://smg.photobucket.com/user/RampageFSJ/media/a4-1.jpg.html
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