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Ed
Ed, Ford Technician
Category: Ford
Satisfied Customers: 211
Experience:  Ford Certified Technican. 10+ years Exp.
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How do i fix a problem with high idle on my 1988 ford ranger?

Customer Question

How do i fix a problem with high idle on my 1988 ford ranger?
Submitted: 8 years ago.
Category: Ford
Expert:  Ed replied 8 years ago.
Hello. First check and make sure there are not any vacuum leaks or a sticking PCV. Verify that the throttle is completely closed and not binding. Then check TPS voltage at idle, should be .9 volt. Then I would suggest unplugging the Idle Air Control while the high idle is occuring. If the IAC is working properly the engine should nearly stall when unplugging. If no change occurs the IAC probably is at fault.
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Customer: replied 8 years ago.
Thanks.....High idle- 88 Ford Ranger: no vacuum leaks, new PCV throttle closed & not binding. TPS voltage at idle is 5 volts, IAC unplugged, engine stalls. Advance ADJ. screw with IAC unplugged, idles OK but ck engine light is on. With throttle control sensor hooked up and electrical plunger of air bypass disconnected, it idles ok with ck engine light off. 12 volt reading at connector, Touch plunger on air bypass and it goes to high idle. Any special way to install TPS?
Expert:  Ed replied 8 years ago.
At the TPS did you measure voltage on the darkgreen/light green wire at idle? This is the signal return, orange/white is VREF and black/white is ground.
Customer: replied 8 years ago.
orange/white
Expert:  Ed replied 8 years ago.
Check on darkgreen/lightgreen wire. Should be about .9 volt closed and raise to 4.5 to 5.0 with throttle fully open. If the voltage is ok we need to look more closely at the IAC circuit. BTW is this 2.3 or 2.9 engine?
Customer: replied 8 years ago.
2.9 engine, dark green/light green .745 at idle, 10 at full throttle.
Customer: replied 8 years ago.
2.9 engine, dark green/light green .745 at idle. At full throttle 1.2 volts. Air bypass white is 8.46 volts and red is 14.3 volts. With plunger assembly and electrical disconnected from the air bypass the motor will idle correctly. Push the plunger on the assembly and the idle goes back up to arround 1250 RPM.
Expert:  Ed replied 8 years ago.
Ok. I do not think it is going to cure everything, but if the TPS is only 1.2 volts at wide open throttle the TPS has a problem. If there is 5 volts between the orange and black wires the VREF to the sensor is ok and the TPS will need replaced and idle voltage adjusted.
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Customer: replied 8 years ago.
Throttle position sensor is new. Air bypass valve is new. What is the correct procedure for putting on the TPS? and how do you adjust the idle voltage?
Expert:  Ed replied 8 years ago.
Been awhile since I did one. But if memory serves me well I believe that you rotate the TPS slightly counterclockwise from where it would line up to the 2 screw holes and slide it over the tab sticking out of the throttle body and then rotate clockwise toward the screw holes. I may have the direction of rotation backwards but if the sensor is oriented right there should be a small amount of spring tension as you rotate it to line up the screw holes. Then install the screws snug, but loose enough to move the sensor. If the sensor is adjustable the screw holes in the sensor body will be oblong. Hook a voltmeter to the green wire and rotate sensor to obtain .85 volt and tighten screws. If the sensor is not oriented to the throttle shaft properly it can break the sensor so be careful.

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Customer: replied 8 years ago.
There are no longated holes on the sensor. If you try to put it in with spring tension the holes do not line up correctly. On one TPS I forced the holes to line up and heard a crack so I put in the new one.
Customer: replied 8 years ago.

Hello Ed,

The Black/white wire going into the TPS has a reading of 70. Light green/dark green is

.745. Orange/white is 5. Maybe the ground wire is a problem? What can I do to fix it?

Expert:  Ed replied 8 years ago.
If the TPS is oriented right once you feel spring tension you should have to rotate it maybe 20 degrees to line up the holes. The TPS reading at idle is lower than I would expect but close enough that I do not believe it will cause a high idle problem. If the voltage was too high the PCM would command the IAC fully open. I have an 88 Ranger that had an intermittant hard start/high idle and a replacement PCM fixed it. I had a spare truck and borrowed the PCM and found the problem that way after chasing IAC's and TPS's and the normal things that you would think is causing the problem. The PCM may be where we are headed.
Customer: replied 8 years ago.

Hi Ed,

What is a PCM and where is it located?

Expert:  Ed replied 8 years ago.
PCM is Powertrain Control Module, it is the engine computer. It could also be called an ECU or ECM depending on who you talk to. It is behind the right lower kickpanel trim below the dash.
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Customer: replied 8 years ago.

Thanks Ed,

I'll replace the PCM. However, I still feel, I haven't installed the Throttle Control Sensor correctly. If I put it in with spring tension, the screw holes do not line up. The air bypass control is getting a wide open signal. Any further ideas?

Expert:  Ed replied 8 years ago.
I just went out and looked at a spare 2.9 I have and the TPS is missing but I will try to find picture of the way it bolts on. Will the sensor line up if you rotate the sensor 180 degrees from where you have been trying to position it?
Customer: replied 7 years ago.

Hi Ed,

$30.00 computer systems tester from auto zone. $8.00 thermostat & $4.00 gasket solved the high idle problem. Thanks for your help eliminating some possibilities. If I have any problems in the future, I will use you again. Bob

Expert:  Ed replied 7 years ago.
Thanks for letting me know what solved the problem, makes me more knowledgeable next time. I can see how this would happen if the stat was stuck open, computer never sees operating temp and stays at high idle.