Mechanics

UNWANTED RPM INCREASE

1995 Ford Taurus

Engine Mechanical problem
1995 Ford Taurus 6 cyl Front Wheel Drive Automatic 130000 miles

I have a 1995 Taurus 3.8 GL that's driving me crazy. It idles around 1,000 rpm in park or neutral. When I put the transmission selector into drive the rpm jumps to about 2500 rpm. It stays there unless I increase the throttle. If I shift into neutral or park the rpm drops immediately to idol speed. This is dangerous and I need help asap.
Thanx, Greg
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Gwarren38
March 22, 2009.



This sounds like you may have an air leak in the intake path. There are quite a few possibilities, so I will start out with the most obvious and easy to check.

Check around the intake path for air leaks. The mass air flow sensor is mounted on the air cleaner assembly. There is a plastic duct going to the intake manifold. With the engine idling, listen for any sounds of air leaks in this area. You can verify a leak by spraying a bit of gum cutter/carb cleaner around any suspected leaks. If there is a leak, the rpm will increase.

Try unplugging the connector from the ISC motor on the throttle body with the engine idling. The engine should drop rpm or possibly stall when you do this. If rpm does not drop, you could have a sticking ISC motor.

Check for trouble codes. A bad coolant temperature sensor can also cause a high idle.

Also, be warned, if the throttle body has been cleaned, it is ruined. The engine will not idle correctly until it is replaced IF it has been cleaned.
Two things that you must NEVER do to a Ford since 1992 - NEVER clean the throttle body, and NEVER back out the idle stop screw. Either will ruin the throttle body, and it will have to be replaced.

Hope this gets you started in the right direction.

Tiny
Jgarofalo
Mar 23, 2009.
Thanx for the response, I'll check for the leaks. The funny thing is after 3 days it went back to normal operation. Imagine that.
The only other question I have is why would the idle speed increase when you put it in gear and decrease when you put it back in neutral?
Thanx again.

Tiny
Gwarren38
Mar 24, 2009.
This is the way the computer is programmed. If the computer sees conditions that indicate a cold engine, it responds as a cold engine should. Ity will increase RPMs when any load is added - like A/C, idling in gear, power steering pressure increase, etc. Also. If the computer sees a mixture too rich, it will admit more air - which raises the RPMs. Too lean, and it admits more fuel - again raising RPMs. As long as the computer is satisfied, the engine will run perfectly. If not, strange problems come up.

Tiny
Jgarofalo
Mar 25, 2009.