Mine is a 93 Taurus, 3.0L, 4spd automatic.
When I first start it up, it runs and idles okay, but after a five minute run down the road at 40-50 mph, the engine idles way too high. Don't know the exact speed. Its a lot more than the high idle I get when the engine is cold, its difficult to hold at a stop, and will take me to 25mph on a flat surface if I let off the brake.
When it does this high idle dance, if I turn off the car, and restart, the idle goes back to normal until the next time I speed on down the road. In fact, if I just click the key off and on, catching the motor before it even shuts off, the problem is "cleared"
If I drive the car around the neighborhood, never really getting past maybe maybe 30 mph, there is no issue. Its seems that if I get it up to 40-50 mph, then the problem of the high idle rears its ugly head.
I have verified that the accel cable is not hung up, the throttle body is clean, and the blades are closed tight when this increase idle speed is occuring. Pressing the throttle at the throttle body does not show any sign of the mechanical throttle being open at all.
I have replaced the TPS, and today swapped in a new IAC valve to no avail. No vacuum leak that I can find, and I tend to rule out anything mechanical since the problem can be 'fixed' by simply turning the key off and on.
There are no codes in the computer, but I would think that 2000 rpm standing still would cause the computer to light the check engine light, and attempt to 'fix' the problem.
Is there some form of a speed sensor that might be bad? The mechanical how-to of the throttle is simple, but I do not know all the details of what tells the computer the information it needs, to control the engine speed. It sure sounds like some form of sensor is giving bad data to the computer control.
I would sure like to hear from anyone with an idea or some conjecture as to where I need to be looking.
The transmission has an issue with 'disengaging' at the stop lights (done it three times in a few hundred miles) which mechanics tell me is a problem with the overdrive circuit, and I am not about to drop $2K to fix the trans, with the engine having this problem, so one thing at a time.
Any chance the trans issue could mess up the computer control of the idle speed? Can't imagine it, but then I don't understand the system. I have a shop manual that touches on the IAC and TPS, but the computer controls are covered in another manual that I have no access to, and cannot find anywhere.
Much obliged for any help or speculation.
John
When I first start it up, it runs and idles okay, but after a five minute run down the road at 40-50 mph, the engine idles way too high. Don't know the exact speed. Its a lot more than the high idle I get when the engine is cold, its difficult to hold at a stop, and will take me to 25mph on a flat surface if I let off the brake.
When it does this high idle dance, if I turn off the car, and restart, the idle goes back to normal until the next time I speed on down the road. In fact, if I just click the key off and on, catching the motor before it even shuts off, the problem is "cleared"
If I drive the car around the neighborhood, never really getting past maybe maybe 30 mph, there is no issue. Its seems that if I get it up to 40-50 mph, then the problem of the high idle rears its ugly head.
I have verified that the accel cable is not hung up, the throttle body is clean, and the blades are closed tight when this increase idle speed is occuring. Pressing the throttle at the throttle body does not show any sign of the mechanical throttle being open at all.
I have replaced the TPS, and today swapped in a new IAC valve to no avail. No vacuum leak that I can find, and I tend to rule out anything mechanical since the problem can be 'fixed' by simply turning the key off and on.
There are no codes in the computer, but I would think that 2000 rpm standing still would cause the computer to light the check engine light, and attempt to 'fix' the problem.
Is there some form of a speed sensor that might be bad? The mechanical how-to of the throttle is simple, but I do not know all the details of what tells the computer the information it needs, to control the engine speed. It sure sounds like some form of sensor is giving bad data to the computer control.
I would sure like to hear from anyone with an idea or some conjecture as to where I need to be looking.
The transmission has an issue with 'disengaging' at the stop lights (done it three times in a few hundred miles) which mechanics tell me is a problem with the overdrive circuit, and I am not about to drop $2K to fix the trans, with the engine having this problem, so one thing at a time.
Any chance the trans issue could mess up the computer control of the idle speed? Can't imagine it, but then I don't understand the system. I have a shop manual that touches on the IAC and TPS, but the computer controls are covered in another manual that I have no access to, and cannot find anywhere.
Much obliged for any help or speculation.
John