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Discussion Starter #1 (Edited)
So..onto my next issue!! The car exhibits an erratic idling issue. It seems to be worse when the A/C is on. This car will be my son's car, so I'm working on as many bugs as possible before he starts driving.
There no codes being generated.
Here's what I see/hear:
  • In general, regardless of hot or cold start, the car will idle anywhere between 500 and 1100RPMs. It is not a consistent occurrence, sometimes the idle might be steady at around 700RPM, sometimes it'll jump.
  • The condition is more pronounced when the A/C is on. There are times when the revs will jump while in gear and if my foot is not firmly on the brake, the car can actually jump forward a bit.
  • I did a "test" in a parking lot by placing the car in Neutral, then shifting to Drive. With the A/C on, the revs jumped when I shifted into Drive. With A/C off, the transition from Neutral to Drive was smooth with no dramatic rev jump.
  • The revs tend to "hang" when lifting off the throttle. eg: In stop and go traffic, if I accelerate to say about 15500 ROM, then lift off , the car will actually HOLD that 1500 RPM then drop, sometimes abruptly, back to idle.
  • This is NOT the same thing as when the transmission downshifts when slowing down and stopping.
  • Unrelated to the idle issue, when the A/C is on, there is a whining noise that almost sounds like power steering, but as soon as the A/C is turned off, the noise goes away!
In my searching so far, some people point to the PCV valve as a culprit, but I've ordered a new TPS. I also intend to clean the MAF and check the throttle cable for binding, especially where the cable attaches to the throttle body/MAF (doesn't feel like it though). It should be okay to spray a lubricant on that section, right?
I have some video I need to look at and then I can try to attach it as well.
https://photos.app.goo.gl/patbHXpypMi2CR8S8 - skip to about 2:50 to see the jump in revs while stopped.
Anyone have any other suggestions on what I can check based on my description?
Thanks!
 

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This new forum format doesn't make it easy to see the type of car you are driving. Erratic idles are usually related to vacuum leak or sticking IAC valve. AC will load up the engine and if IAC doesn't respond well the idle will go crazy. I also had a IAC try to keep my MPH on the highway for a few seconds after I took my foot off the pedal. I had to use my brake pretty heavy in stop and go traffic. I return the IAC to Advanced Auto and got a junkyard IAC and all worked well. Try removing the IAC and clean and oil it.
 

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Try using the search box above with 'IAC cleaning" as your search argument. If the IAC ends up requiring replacement use only a Motorcraft part, aftermarket IACs have caused far more problems than they ever solved
 

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Discussion Starter #5
Thanks all. The car is a 2007 SEL. Interesting that you point to the IAC valve, as that was one of the things the dealer had done on the car ("r&r Idle Air Control valve) and it looks relatively new. I'll check it out just the same!
 

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Discussion Starter #6 (Edited)
UPDATE:
Hard to believe it's been this long since I said anything on this issue. So, after I couldn't get to the heater core to fix that, I did some other work; namely, I threw everything else at it>
New IAC; New TPS; and New PCV Valve and New Thermostat
As most people have told me, the IAC was probably the main culprit, I decided to just put everything on.
After my friend replaced the heater core, he told me that the transmission is probably on its last leg, which what I don't really want to hear now. Like I mentioned, this is my son's car, and I want it to be as solid as possible.
The car runs and idles WAY better than it ever has since I bought it, but there is still fluctuation in engine speed WHILE driving. The car doesn't buck or jerk, but you can see the tach fluctuating.
Additionally, the transmission DOES at times, shift erratically as in kind of hard shifts from 1st to 2nd when accelerating from a light for example. Sometimes, when accelerating from a stop and turning, the revs will increase sharply and then the tranny shifts harder. Sometimes when merging onto a highway in traffic, revs will fluctuate as speed increases, but speed actually increases. So it's not like the engine is racing and the car doesn't go faster. Once at highway speed, the car run perfectly.
Yuu can see the RPM fluctuation in the videos attached. Steady state highway cruising with the A/C on. If I turn the A/C OFF, engine speed is STEADY.
I just find it hard to believe that A/C operation would affect engine speed as much as it does. So I don;t know if I have a transmission issue or an engine issue or a combination of the two. If need to post this somewhere, please advise. Any thoughts?

Videos here: New video by Dean Irwin and New video by Dean Irwin
 

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This new forum format doesn't make it easy to see the type of car you are driving. Erratic idles are usually related to vacuum leak or sticking IAC valve. AC will load up the engine and if IAC doesn't respond well the idle will go crazy. I also had a IAC try to keep my MPH on the highway for a few seconds after I took my foot off the pedal. I had to use my brake pretty heavy in stop and go traffic. I return the IAC to Advanced Auto and got a junkyard IAC and all worked well. Try removing the IAC and clean and oil it.
I agree with this dude, I ran into the same issue twice. There's no delaying a bad IAC, when it goes that's it.
 

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Up through G-4 idle speed is not managed to fix other issues. Stuck or high flow EGR will just result in low or high idle. You have to fix the problem. I am sure the designers did not want the system to cover up things needing to be fixed.
Idle speed is managed by air flow as is power. Idle speed works fine if no or minimum air gets in besides the throttle plate, IAC, PCV. Sources of non managed air, are leaks. Lots of places for leaks.
Any cheap PCV will result in bad idle. Often missed: fresh air to the crankcase which is filtered and metered by the MFM. Leak in fresh air hose is not a vacuum leak, it just lets un-metered air into the system and upsets the PCM. EGR leaking can mess up idle without causing fuel trims tell tale numlbers. Long term fuel trims move around all the time so a screen shot does not tell. If idle numbers are highter than load numbers, likely air leak.
-chart-
 

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I prefer "Carchip" device which records things you choose. See pic, TPS signal should always return to the same value. Circled are non repeating values at idle stop. Car had erratic idle speed. I suspected the TPS and replaced it with new OE part. No change. I back probed the TPS and found 5V reference very steady. Output unsteady. "Return" = ground unsteady. The return line of all sensors lead to a ground on the firewall pas side. Eyelet corroded and bolted over paint and rusty. Cleaned, sanded, and treated with anti corrosion electric compound and issue fixed.
I am a fan of "Carchip" as it lets me record and then see events on my computer later for evaluation. Chart shown is my own making from it's data. Ford's grounding is a VERY weak part of these cars. DOY fixes this and saves a lot of poor performance. In this case, PCM, and all sensors had a bad and erratic ground. Wonder it ran at all.
Carchip recording also showed up charging system, random high volts, and low volts. I replaced the Alt as there is no fix for a bad regulator.
-chart-
 

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Discussion Starter #11
Up through G-4 idle speed is not managed to fix other issues. Stuck or high flow EGR will just result in low or high idle. You have to fix the problem. I am sure the designers did not want the system to cover up things needing to be fixed.
Idle speed is managed by air flow as is power. Idle speed works fine if no or minimum air gets in besides the throttle plate, IAC, PCV. Sources of non managed air, are leaks. Lots of places for leaks.
Any cheap PCV will result in bad idle. Often missed: fresh air to the crankcase which is filtered and metered by the MFM. Leak in fresh air hose is not a vacuum leak, it just lets un-metered air into the system and upsets the PCM. EGR leaking can mess up idle without causing fuel trims tell tale numlbers. Long term fuel trims move around all the time so a screen shot does not tell. If idle numbers are highter than load numbers, likely air leak.
-chart-
What is the "MFM" please?
 

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Discussion Starter #12
I prefer "Carchip" device which records things you choose. See pic, TPS signal should always return to the same value. Circled are non repeating values at idle stop. Car had erratic idle speed. I suspected the TPS and replaced it with new OE part. No change. I back probed the TPS and found 5V reference very steady. Output unsteady. "Return" = ground unsteady. The return line of all sensors lead to a ground on the firewall pas side. Eyelet corroded and bolted over paint and rusty. Cleaned, sanded, and treated with anti corrosion electric compound and issue fixed.
I am a fan of "Carchip" as it lets me record and then see events on my computer later for evaluation. Chart shown is my own making from it's data. Ford's grounding is a VERY weak part of these cars. DOY fixes this and saves a lot of poor performance. In this case, PCM, and all sensors had a bad and erratic ground. Wonder it ran at all.
Carchip recording also showed up charging system, random high volts, and low volts. I replaced the Alt as there is no fix for a bad regulator.
-chart-
What is "DOY" please? It's interesting that you mention replacing the alternator. My next question was going to be where the regulator was, as the headlights and dash lights do flicker often. Not badly so, but enough to notice. Just one thing else.. the engine speed fluctuation is while driving..it DOES fluctuate at idle, but once I replaced the IAC, PCV and TPS, nowhere as bad as it used to.
 

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Something just dawned on me, you mentioned the engine revs fluctuating as it's moving? Has the speed sensor on the top of roughly the differential been replaced? That could be a culprit, and honestly I hope it is. The Taurus line wasn't know for it's bulletproof transmissions however there are a few things that could simulate a failing transmission on them.
 

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Discussion Starter #14
Something just dawned on me, you mentioned the engine revs fluctuating as it's moving? Has the speed sensor on the top of roughly the differential been replaced? That could be a culprit, and honestly I hope it is. The Taurus line wasn't know for it's bulletproof transmissions however there are a few things that could simulate a failing transmission on them.
Probably not! Something else to check out while I have the time these days! Thanks!
 

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Discussion Starter #15
I need to find more information on the grounds too. Are there any resources on that? I'll check around and see as well..
 

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DIY should be and is "do it yourself".
Pic of chart of Alt with erratic performance. Also had it peak at 15.3 at one point. The regulator is inside the Alt in the vast majority of cars. I replaced this Alt with a NEW one. Rebuilt Alts recycle the regulator and just put new brushes in it. I'm a bit paranoid for a reason. Lin Cont uses the same Alt as the Bull G-4 in DOHC . I had 2 regulators fail on my '02 Lin. First one cost me $530 and a night in a motel. Next time I did it myself. ~2.5 hours hard labor to do that. Second one caused me to miss a trip in that car.
-chart-
 

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