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Galane · 05-25-2019, 07:27 PM

I have a 1998 Taurus LX with the DOHC V6. It has a bit over 108,000 miles on the odometer.

It got to running very badly so I changed the spark plugs and wires, cleaned the intake manifold (the rarely used secondary intake butterfly valves and tube get really cruddy on this engine), cleaned the throttle body and the almost completely clogged IAC passage.
I also installed a new, genuine Motorcraft PCV valve, replaced the oil soaked and partially collapsed hose from it to the underside of the intake.

After putting it back together it runs great but keeps wanting to "idle" at up to 1500 RPM or more. I can usually force it to slow to a proper speed around 900 RPM by holding the brake and shifting to Drive, where after a bit it will (sometimes) slow down.

Since the IAC valve was very filthy I installed a new one, making sure to get the right one for the DOHC V6, considerably higher priced than for the pushrod V6 since only around 10% of Tauri of this generation had the DOHC. Also replaced the throttle position sensor, didn't buy the bargain basement nor the highest overpriced one. Neither had any effect on how it misbehaves.

What it seems to be doing is pulling the IAC fully open, as though it's compensating for an almost completely blocked IAC passage. The damn thing will take off and go over 25 MPH without my foot on the gas! Some of the time I can pull over and stop and hold the brake until it drops to a normal foot off the gas idle speed - but then some of the time it will soon want to rev back up and take off again.

On top of being very irritating how it went from running great to suddenly crappy, then after being given a tuneup it won't work correctly - it gets terrible in town MPG with it wanting to "idle" so fast and having to keep using the brake to slow down. Then there's the wear that's putting on the brake pads.

I asked at the Taurus forum and all I got there was insistence that it has to be a vacuum leak. Shouldn't be that because a vacuum leak wouldn't cause it to shift among idling properly, running at 1,000 RPM, running at somewhere between 1,000 and 1,500, running at 1,500, or running at faster than 1,500. A vacuum leak should give a *consistent* improper idle speed.

05-25-2019, 07:27 PM	#1 (permalink)
Galane Master EcoModder Join Date: Jul 2009 Location: idaho Posts: 282 Thanks: 0 Thanked 96 Times in 74 Posts	How do I fix 98 Taurus high idle? I have a 1998 Taurus LX with the DOHC V6. It has a bit over 108,000 miles on the odometer. It got to running very badly so I changed the spark plugs and wires, cleaned the intake manifold (the rarely used secondary intake butterfly valves and tube get really cruddy on this engine), cleaned the throttle body and the almost completely clogged IAC passage. I also installed a new, genuine Motorcraft PCV valve, replaced the oil soaked and partially collapsed hose from it to the underside of the intake. After putting it back together it runs great but keeps wanting to "idle" at up to 1500 RPM or more. I can usually force it to slow to a proper speed around 900 RPM by holding the brake and shifting to Drive, where after a bit it will (sometimes) slow down. Since the IAC valve was very filthy I installed a new one, making sure to get the right one for the DOHC V6, considerably higher priced than for the pushrod V6 since only around 10% of Tauri of this generation had the DOHC. Also replaced the throttle position sensor, didn't buy the bargain basement nor the highest overpriced one. Neither had any effect on how it misbehaves. What it seems to be doing is pulling the IAC fully open, as though it's compensating for an almost completely blocked IAC passage. The damn thing will take off and go over 25 MPH without my foot on the gas! Some of the time I can pull over and stop and hold the brake until it drops to a normal foot off the gas idle speed - but then some of the time it will soon want to rev back up and take off again. On top of being very irritating how it went from running great to suddenly crappy, then after being given a tuneup it won't work correctly - it gets terrible in town MPG with it wanting to "idle" so fast and having to keep using the brake to slow down. Then there's the wear that's putting on the brake pads. I asked at the Taurus forum and all I got there was insistence that it has to be a vacuum leak. Shouldn't be that because a vacuum leak wouldn't cause it to shift among idling properly, running at 1,000 RPM, running at somewhere between 1,000 and 1,500, running at 1,500, or running at faster than 1,500. A vacuum leak should give a consistent improper idle speed.