How to tell if my 1997 IAC is bad? - Taurus Car Club of America : Ford Taurus Forum
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post #1 of 10 (permalink) Old 04-17-2019, 08:18 PM Thread Starter
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How to tell if my 1997 IAC is bad?

I have a 97 LX. It got to running real crappy so I installed new plugs and wires, a new PCV valve, replaced the U shaped rubber hose from the PVC to bottom of the intake and the two rubber parts in the line from the air intake tube to the front valve cover. Also cleaned the throttle body (back side of it was dirrrrty), lower intake and secondary valves as good as possible and flushed the upper intake with solvent. The IAC passage was just about totally blocked, now it's not.

The plugs didn't look all that bad, I suspect it was the almost blocked IAC passage was causing the bad idle, just took getting on the gas a little to make it run mostly better.

Problem is now most of the time it wants to idle over 1,000 RPM. City gas mileage is not very good now. Acceleration from stop to 55 is very nice, an I wasn't pushing the pedal close to the floor.

No check engine light, no codes. I had the battery disconnected while doing the work.

I suspect it's an ex-rental fleet car due to it having a 7,000 RPM tach when an LX with DOHC V6 was supposed to have an 8,000 RPM tach. Does have the 120 MPH speedometer. Another "thing that makes me go hmmm" is the PCV tube and hose from the intake duct to the front valve cover is not at all like the photo of the Dorman (or other brands) replacement for that part for a 97. It has a 90 degree rubber elbow at the valve cover and the "why is this here?" 90 degree connection at the intake tube that requires the special shaped hose - when a perpendicular connection and straight hose would have been the logical choice. Dorman's replacement has what looks to be a less than 90 degree valve cover elbow and incldes a plastic tube that's not the same shape, assuming they have the right photo. Why would I want to replace the hard tube when there's nothing wrong with it, and it doesn't include the rubber hose to the intake duct. I've owned and/or worked on a lot of fleet vehicles and most of them have had "This doesn't exist." or "We never made that." combinations of parts which make them difficult to find the correct parts for repairs. (Ask me about a 2004 Dakota with a V8 made *mostly* of early 2003 parts that shouldn't have been in that truck.)



BTW, every time I work on newer cars I wanna swat whomever designs them with the PCV connected to a dry part of the intake. All that does is cause crud buildup. If it was routed to a wet part of the intake, there would be no buildup problems. Even a GOOD vapor/oil separator would help. I've seen ONE car with a factory PCV oil separator, a 1994 Oldsmobile Achieva, but it was a *bad* separator that hardly did anything. It had some filter in it like a chunk of a washable furnace filter. It would get coated with oil then it would go through and grunge up the inside of the intake.

Last edited by Galane; 04-17-2019 at 08:28 PM.
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post #2 of 10 (permalink) Old 04-17-2019, 08:30 PM
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Fwiw, your pcv valve sits in an oil separator tube. Did you happen to clean the "c-channel" behind the tb gasket on the face/throat of the uim? It's important to clean this and its 3 notches at the bottom. Also, clean the hole and tunnel in the top left of the "c-channel" as this is the passageway from the egr valve. You can clean the iac with intake, tb or carb cleaner, but keep the elec. end elevated. Don't get that end wet.

Last edited by sheila; 04-17-2019 at 08:34 PM.
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post #3 of 10 (permalink) Old 04-18-2019, 02:38 AM Thread Starter
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Join Date: Sep 2012
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I flushed all the passages in the upper intake. It wants to idle well over over 1,000 RPM. After letting it sit and warm up sometimes the idle will drop, most of the time it wants to stay high. There's a connection on the back of the upper intake near the throttle body, with two small hard vacuum lines. I had to put a zip tie on it to get it to stay on. I noticed it had fallen off while I was taking the upper intake off.

Last edited by Galane; 04-18-2019 at 02:41 AM.
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post #4 of 10 (permalink) Old 04-18-2019, 10:29 AM
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^+1. Those small hard red/green lines supply vacuum to/from the egr, fpr and evr. Green- from evr to egr. Red- to fpr & to evr.
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post #5 of 10 (permalink) Old 04-18-2019, 01:57 PM
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People say aftermarket PCV valve will screw up the idle on these engines and also vacuum leaks will cause a high idle.
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post #6 of 10 (permalink) Old 04-18-2019, 02:06 PM Thread Starter
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Quote:
Originally Posted by Automender12345 View Post
People say aftermarket PCV valve will screw up the idle on these engines and also vacuum leaks will cause a high idle.
I used a genuine Motorcraft PCV valve.
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post #7 of 10 (permalink) Old 04-18-2019, 03:56 PM
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+1 for possible vacuum problem
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post #8 of 10 (permalink) Old 04-27-2019, 04:58 AM Thread Starter
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Join Date: Sep 2012
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I replaced the IAC yesterday. Bought a new one off eBay because due to the DOHC V6 being a rare option companies want to really gouge on the price for parts for it (and the V8). Makes me wonder if there's really any difference in the IACs for the three engines other than the connector position.



I started the car and it went up to 1500 RPM for a bit then dropped to 1000, then down a bit more to just under the 1K mark. Call it 900. All good now, right?


Nope. A few hours later I took it for a drive and idle speed was still erratic. Part of the time it would idle correctly, part of the time it wanted to run 1500 with my foot off the gas, despite being warmed up. Once it wanted to "idle" at 2000. But overall less time spent at the wrong RPM. If it was a vacuum leak it ought to run consistently at the wrong idle speed.



Still no check engine light. Seems like it may be the TPS on the way out. Apparently the almost fully clogged IAC passage had been masking problems until the plugs and/or wires got so bad it'd barely run without pressing the gas pedal some. Or possibly the IAC passage had become completely blocked off. It does have almost 110K miles on it.
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post #9 of 10 (permalink) Old 04-27-2019, 01:46 PM
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Aftermarket IAC of Motorcraft part? Aftermarket IACs dont work well.
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post #10 of 10 (permalink) Old 06-09-2019, 04:14 AM Thread Starter
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Join Date: Sep 2012
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Doing the idle relearn seems to have fixed the *warm* idle but it still wants to run wild when *cold*. Yesterday I was driving in town when it revved itself over 2,000 RPM, sped up to 35 MPH and was still accelerating before it started to warm up, then dropped down to proper idle speed.

That is just nucking futz that it's capable of revving that high and going that speed *without my foot on the gas*!

How do I get it to learn the proper COLD idle speed? Before it got to running bad it was FINE. I could just start it and drive away, no matter the temperature. It would idle at the proper RPM. I'd have the battery disconnected for various things, never had to do anything to have it relearn anything, it Just Worked.

All I had to do with it before was change the transmission fluid and filter (with a bottle of Lucas to fix the slamming into first) and put on a new belt and tensioner at that time, changed the oil pan gasket at 93K miles, changed the water pump and had a rebuilt AC compressor installed at 106K because the AC clutch pulley bearings went to pieces. AC still worked but I figured may as well replace the compressor too, my luck the compressor would blow a week after changing the clutch.

Has around 108K on it now.

I have a VCM2 clone, which has had regular firmware updates from Chinacardiags. Software says there's a newer calibration for the car but flashing fails, claims it "can't communicate with the PCM" despite it being able to communicate with it to do all sorts of other things.
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