1999 Ford Taurus - 3.0L Hot Restart Idle Speed

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Tim Martin
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1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Tim Martin »

I got this 1999 Ford Taurus, 3.0L OHV vin U engine, 68,000 miles on it that after a hot soak restart the engine will rev quite high 2,500 rpm, back to almost shutting off, back up to very high rpm and back down. It will repeat this cycle several times before settling in to the desired idle speed. There is no codes, fuel pressure is within specs, tps is .87v at closed throttle and barometric pressure is 156 khz koeo. By a hot soak, I mean driving say for 1/2 hour then shutting off an then 15 minutes later trying to restart it an go. This is when this high idle speed will happen. At times the engine will shut off when it comes back down. It has been at another garage an they replaced the idle air control valve. I know, that is the first thing that came to my mind so unless the replacement one is also faulty that is not the problem cause it functions the same as the old one. One of my questions is what does the PCM look at to determine idle speed on a hot restart? Could I have a bad camshaft synchronizer" If so, wouldn't that set a code? Or might I have a PCM that needs recalibration?
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Re: 99 Taurus Hot Restart Idle Speed

Post by Rich »

Smoke test intake system.

my 1st thought was IAC. my tech says smoke it, you have a vacuum leak
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Re: 99 Taurus Hot Restart Idle Speed

Post by Tim Martin »

Well, ya know, I thought a that too but I also woulda thought that MAF reading would show that, not? By the way, MAF at idle is 6.5 grams.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by ricmorin »

The MAF is upstream from a vacuum leak, so it's considered unmetered air.

Check the fuel trims when the symptom is there.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Jeff @ Able Auto »

For what it is worth....I just went thru this with a Windstar 3.8. The first 2 I installed had a plastic nose and kept doing the same thing. Installed a third one, upgraded to aluminum nose and it was fixed. The plastic valves were an economy line from NAPA and I had never had a problem with them in the past but you can bet I won't be using them in the future.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by steven kiser »

Another thing along with all the other good ideas here is to see if some idiot tried to screw with the mechanical idle. I've seen more than a few where the base idle has been screwed with causing this issue. I've also seen IAC's improperly installed or even backwards, cracked intakes, vac leaks (that a smoke machine shows or even a quick spray of carb cleaner will show. Carb cleaner should only be used to identify not isolate. I also use propane, I attached a 3/16th hose to the bottle so I get it into tight spots.) This does sound more of a throttle issue where someone screwed with the screw or bent something to make it idle high. It's searching for an idle causing it to roam. It also could be a temp issue but I kind of doubt it.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Tim Martin »

Ford uses IAC percentage values. An, I know, these percentage values are somewhat relative but what typically should those numbers be? This one is at 34 percent at a hot idle. Is that ok? Idle speed rpm is within spec both cold an hot.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by jbadenoch »

34 percent is pretty normal for idle. Ive seen them aroung 45 or higher with vac leaks. Ive seen a LOT of ford idle issues due to dirty throttle plates, intake cleaner works pretty well.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Tim Martin »

Well, you bring up the thought of a dirty throttle bore an I thought of that as well but this one is spotlessly clean. I suspect a previous shop cleaned it. So it really has me somewhat puzzled. Regarding IAC pecentage, does this system work in the reverse of GM older system where a lower number indicates a vacuum leak? In other words, 25 percent could indicate a vacuum leak whereas 35 could be fairly normal, or isnt that how it works on these?
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by brother bubba »

...

You are right, Tim. With a massive vaccum leak, IAC will drop all the way to zero. 30-35 is optimal for steady idle.
I would suspect the IAC itself until I proved to myself otherwise.

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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by jbadenoch »

to be sure on the iac percent, create a vac leak while watching percentage. 30-35 is normal. Doesnt sound like vac leak or plate, based on info.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Tim Martin »

jbadenoch wrote:to be sure on the iac percent, create a vac leak while watching percentage. 30-35 is normal. Doesnt sound like vac leak or plate, based on info.
Great Idea! Now I am wondering why I didnt think of it.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by steven kiser »

After putting some thought into this the base idle wouldn't allow vehicle to stall just by an IAC issue. I would look into a weak E.G.R. solenoid or valve. Looking at this from the inside out the IAC is doing it's job. The key here is hot soak and I'm thinking it's something that's been activated after warm up and doesn't completely reset after shut down. During the drive cycle the EGR should be opening and closing while driving. If the solenoid is weak or getting a false signal on restart it will allow the valve to open and this will most definitely cause a surge and stall. The IAC is doing it's job but as a rule, in my shop, with issues like this, I would solve the issue and since I'm the shop that the customer is going to come to with idle issues I would replace the IAC with one that I would've used if I replaced it. I can't and won't stop preaching on this issue because I've had people come back screaming that their vehicle is screwing up again and when I look into it it's a part failure from the shop that worked on it before I did. I know I'm rambling again but the case I'll use is a vehicle came in with a rough idle and stalling after another shop worked on it. The vacuum hoses were all screwed up and the EGR was hooked up to direct vacuum causing the issue. I straightened it all out resolving the customers complaint. That vehicle came back numerous times and the customer felt that since I was the last one to work on it I was the one that screwed up. IT boiled down to damaged plug boots, incorrect plugs and gaps that ranged from 30 to 65. From that point on I became a remove all and replace with parts I would have installed if I were the original shop. The only time I won't do this is when the vehicle is brought to me by another shop and I'm not directly involved with the customer. I have had issues where I've had vehicles sublet to my shop and the shop the person was dealing with told them I was the one that repaired it. They came to me complaining and I told them that I told the shop that brought the vehicle to me that there were other issues and they told me not to do anything more. I was able to explain to the person that owned the vehicle that the only way I would deal with the vehicle was to completely strip it of all previously installed parts and repair it to my specifications.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Tim Martin »

Steve, I understand where you are coming from an agree with your logic per the heat soak idea. The other thing I noticed while driving this car is that at times when I stop at a traffic light, the idle is at 2,000 an I really got to put pressure on the brake pedal so I dont have a runaway. (Customer didnt tell me this) If I put the gearshift lever in neutral, the engine revs all the higher an in a few seconds drops back to normal an if I let in in gear, it does the same. During that high idle, the IAC percent is in the low to mid fifties telling me the IAC is working. I am forced to conclude, as Steve is suggesting, that the issue is an induced high idle caused by another issue. The kicker here is it is very erratic and nothing consistent about it. I thought of an EGR issue also but typically if the EGR is faulty at whatever level, the engine runs rough an this one doesnt. I could unhook the EGR valve for testing purposes while driving however I am thinking that would be a waste of time.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by Jeff @ Able Auto »

I caught the windstar by watching the IAC counts during the occurrence. The IAC commands would change rapidly then the engine would surge/stall. The IAC was not reacting as fast as the computer was commanding.
I have another Ford coming in next week for the same condition. 2000 Taurus with 3.0 pushrod motor. Put an IAC on a month ago for surging, worked good till yesterday. I really believe it is the quality of parts we are getting. This Taurus has a Delco replacement part installed.
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Re: 1999 Ford Taurus - 3.0L Hot Restart Idle Speed

Post by nickscarcare »

This Taurus has a Delco replacement part installed.

There is the problem a GM part on a Ford!!! LOL :lol: :lol:
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