Idle issues are common on these cars, especially 5-speed cars. EGR Valves, Idle Air Bypass solenoids and Throttle Position Sensors are common causes. A bad connection with the 10 pin (salt and pepper shakers) black and white engine electrical connectors can also cause poor idle quality. To ensure a good connection on the 10 pin connectors a little modification can be done which is fairly easy and will cure some surging and hanging idle issues on 86-93 Mustangs and should be the first thing done when tackling any idle issues.
10 Pin Connector modification:
1. Take the 10 pin connectors apart (salt and pepper shakers).
2. use a pick like tool to spread the male terminals open more so they make better contact. In the center of each male terminal there is a small seam and seams down the sides of the terminal which allows you to spread them open.
3. Apply some dielectric grease to the terminals
4. Plug the connectors back in.
Throttle Position Sensor (TPS) adjustment:
Without the proper adjustment, the throttle position sensor (TPS) will give the computer false reading as to the exact throttle opening. A false reading will limit wide-open throttle performance. A voltage reading must be taken using a digital volt/ohmmeter (DVOM) with the Key On/Engine Off and with the Key On/Engine Running.
The TPS is located directly on top of the throttle body and is adjusted by loosening the two Phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small drill bit or a small file to achieve the desired reading. The spec range for Key On is from .88 to 1.0 volts; shoot for .90 to .98 volts. Make sure voltage reaches/exceeds 2.71v at WOT.
Incorrect Throttle Position Sensor (TPS) voltage will result in reduced performance including a possible hanging/surging idle. The best way to take a TPS voltage reading is by using two safety pins through the wires coming from the sensor. The positive lead is attached to the green wire, while the negative goes to the black wire. Always ground the meter through the sensor's black wire. This gives a direct, and more
accurate ground into the computer.
Resetting the base idle:
Clear the computer's idle memory by disconnecting the battery for 20+ minutes.
-Disconnect the Idle Air Bypass solenoid
-Reconnect battery
-Start the engine and set the idle speed to the desired RPM with the idle screw on the throttle body
-Turn off the engine and reconnect the air bypass solenoid
-Set TPS voltage between 0.90 - 0.95 volts with a digital volt meter
-Start the engine and let it idle for 2 minutes with no accessories on.
-Turn off the engine for two minutes
-Start the engine again and run for 2 minutes with every accessory turned on.
-Turn the engine off again.
10 Pin Connector modification:
1. Take the 10 pin connectors apart (salt and pepper shakers).
2. use a pick like tool to spread the male terminals open more so they make better contact. In the center of each male terminal there is a small seam and seams down the sides of the terminal which allows you to spread them open.
3. Apply some dielectric grease to the terminals
4. Plug the connectors back in.
Throttle Position Sensor (TPS) adjustment:
Without the proper adjustment, the throttle position sensor (TPS) will give the computer false reading as to the exact throttle opening. A false reading will limit wide-open throttle performance. A voltage reading must be taken using a digital volt/ohmmeter (DVOM) with the Key On/Engine Off and with the Key On/Engine Running.
The TPS is located directly on top of the throttle body and is adjusted by loosening the two Phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small drill bit or a small file to achieve the desired reading. The spec range for Key On is from .88 to 1.0 volts; shoot for .90 to .98 volts. Make sure voltage reaches/exceeds 2.71v at WOT.
Incorrect Throttle Position Sensor (TPS) voltage will result in reduced performance including a possible hanging/surging idle. The best way to take a TPS voltage reading is by using two safety pins through the wires coming from the sensor. The positive lead is attached to the green wire, while the negative goes to the black wire. Always ground the meter through the sensor's black wire. This gives a direct, and more
accurate ground into the computer.
Resetting the base idle:
Clear the computer's idle memory by disconnecting the battery for 20+ minutes.
-Disconnect the Idle Air Bypass solenoid
-Reconnect battery
-Start the engine and set the idle speed to the desired RPM with the idle screw on the throttle body
-Turn off the engine and reconnect the air bypass solenoid
-Set TPS voltage between 0.90 - 0.95 volts with a digital volt meter
-Start the engine and let it idle for 2 minutes with no accessories on.
-Turn off the engine for two minutes
-Start the engine again and run for 2 minutes with every accessory turned on.
-Turn the engine off again.
however i noticed that if i pump the brake the surge goes away. is that a vacuum leak and if it is will the leak cause the surge? thanks
