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Old 05-25-2019, 07:27 PM   #1 (permalink)
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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.

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Old 05-26-2019, 10:23 AM   #2 (permalink)
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Certainly doesn't hurt to recheck any work done. Check anything that was removed or unplugged. Had a ZX2 that did similar, it was a vac leak in the PVC line. Replaced a temp sensor but the fuel trim showed constant adding fuel at idle. Good luck!
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Old 05-26-2019, 10:52 AM   #3 (permalink)
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I would clear the keep alive memory. Disconnect the battery for a few minutes. I use a scanner to do this but I think a battery reset will do the same thing. Let us know if this helps. Do you have a code reader with a data stream?
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Old 05-27-2019, 12:39 AM   #4 (permalink)
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I have a Harbor Freight 60794. Identical to the Autel MS609. Takes the same updates. Last update was 12/25/2013. I bought it used because it was supposed to read ABS codes, but of course it wouldn't read (or wouldn't *properly* read) the ABS module on a 1998 Mercury Mountaineer, falsely claiming 'no codes stored' when Autozone's reader could read it.

I also have ForScan, which I've used pretty often to program new keys. It works with the VCMII clone I have from ChinaCarDiags. They quite frequently put out firmware updates for it, which is surprising. I expected it to be one of those 'throw it on the market then do squat' things like cheap Chinese Android tablets that never get updates.

I cleared the KAM in the ECU but that changed nothing. Probably should do the P1000 drive cycle but there's nowhere around here that's ideal for that. Would be nice if there was some place that had a dyno, or even just some rollers to put it on to run it through that.

Last edited by Galane; 05-27-2019 at 12:47 AM..
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Old 05-27-2019, 11:31 AM   #5 (permalink)
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This is from the fsm on idle control.
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Old 05-27-2019, 04:10 PM   #6 (permalink)
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Once you clear the ecm, which it seems you have, let it sit and idle for a good long while (enough to get up to temp and run for a few minutes more) and see if it figures itself out. My older cars needed to do this when they were "Reset". They wouldn't come down if I kept interrupting it by driving or otherwise messing with the throttle.

Check the OBD2 signals to make sure it's registering the coolant temp properly, and the air intake temp as well. Stuck open EGR valve might do it. Leaky exhaust manifold might make it try and compensate for a lean condition. YMMV.
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Old 05-27-2019, 07:29 PM   #7 (permalink)
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Quote:
Originally Posted by me and my metro View Post
This is from the fsm on idle control.
Too small for my 48 year old eyes that are both myopic and presbyopic to read.
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Old 05-28-2019, 01:24 AM   #8 (permalink)
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It says after reseting the KAM you must idle the engine for approximately 15 minutes. It needs to run in neutral with the a/c on and with the a/c off, also it needs to run in drive with the a/c on and off. It needs to relearn how to idle properly.
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Old 05-28-2019, 10:35 PM   #9 (permalink)
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Quote:
Originally Posted by me and my metro View Post
It says after reseting the KAM you must idle the engine for approximately 15 minutes. It needs to run in neutral with the a/c on and with the a/c off, also it needs to run in drive with the a/c on and off. It needs to relearn how to idle properly.
That seems to have done the trick. I ran it through that sequence twice, got it warmed up then let it go for at least a minute each in park and drive, with and without the AC on.

Then I went across town to McDonalds and it didn't try to rev up and take off on its own.

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