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Erratic Idle Speed Problem (possibly related to A/C operation)?

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#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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#2 ·
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.
 
#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
 
#8 ·
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-
 
#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?
 
#9 ·
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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#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.
 
#13 ·
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.
 
#16 ·
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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#17 ·
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-
Okay, thanks. You had "DOY" in your response, that's why I asked.
 
#18 ·
I don't know y'all. I'm think I'm beginning to lose faith in the car. There are so many inconsistencies that are appear to be transmission related..I have to really think about whether I'd want my son in this car.. Let me try to summarize all I've seen/experienced so far with the transmission.
1. The aforementioned fluctuation in RPMs at highway speed when the AC is on (Post #6) - Video Here and Here
2. Erratic shifting between 1st and 2nd, but WHEN it does it is what's confusing!
a. Accelerating from a stop AND making a LEFT turn... Seriously.. When leaving a light or stop and making a LEFT TURN, it appears to slip in 1st, then hunt a couple times and finally get
2nd...WEIRD! I can ALWAYS replicate this... the audio is pretty quiet but you can hear it here
3. Every so often, when accelerating and turning, ESPECIALLY if I don't come to a complete stop and WAIT for a second, I can get RPM hunt and then an actual HARD shift (bang) ..and this is even after I've backed off the gas.. Yes, I've become VERY sensitive to the RPMs on this car..lol
4. If I have to come to an ABRUPT stop, that just confuses the car... Abrupt drop in RPMS (never stalls); RPM hunt then one or two lurches as the transmission appears to be trying to figure out
what to do. This happens even when I'm still on the brakes.

I'm kicking myself now about changing the trans fluid, because I never really saw these issues (except for the highway speed RPM fluctuation) until after the fluid was changed. I know most people say don't change it if you don't know the history, but a few other people I spoke to also said they changed fluid and did not have an issue. Maybe it was bound to happen regardless?
I came across a couple videos about the transmission vent, so I checked that today. The cap was fully down so I removed it and made an incision in the top just like shown here. The vent did not appear to be clogged and when I replaced the cap, I made sure that it was not all the way down but that didn't appear to make any difference when I went on a test drive. I found and checked the grounds and they are all tight and pretty clean.
I'm thinking now that my friend is right about the transmission being on its last legs.
It's a shame because outside of this, the car drives extremely well for the mileage (189,514). Once it gets into 4th gear on the highway, it's fine, drives perfectly and quietly with no fuss at all.
If you've lasted through this post to the end, what are your thoughts?
 
#21 ·
UPDATE: After all the advice offered here and online, and before embarking on getting and installing a VSS, I checked the transmission fluid level (THE PROPER WAY).
The dipstick was pretty much DRY with the engine running... it took 3.5 quarts to get the fluid to the correct level.
So now I have to see if I have a serious leak somewhere. There's no smoke when driving and the fluid doesn't smell burnt. I would smell fluid a couple times before, typically when coming to a stop, but it would not last.
Can a car actually consume/burn transmission fluid? Or is it possible that when I had the fluid changed last year around late September, that it was never filled properly?? I usually check whenever fluid changes are done on my vehicles, but somehow, didn't do it on this car. I don't have time to DIY as much anymore so I take all our cars to a fast lube place I've used for years with no issue for fluid changes.
Anyway, the addition of the fluid has made the car drive SO much better.
SO the next step is to clean the engine and underbody in an attempt to see where leaks are coming from. As I mentioned previously, the vent cap was fully on, so I removed, cleaned and also modded it as shown by a guy on You Tube.
Thanks as always for your advice. I'm just happy the car is actually driving decently now.
 
#24 ·
UPDATE: I think I've discovered the leak. So, on the 13th, I put the car on ramps, and used brake clean liberally to clean the trans pan. I think I also found the source (or one of the sources) of the leak..see "Clean" and "Leak" pics. Drove all week with no issues, then put the car back on the ramps today, found leakage (some of which COULD be from the car being inclined?) but also found more leakage form the same location, which I'm assuming is where the dipstick tube goes into the transmission? See "Today" pics and video.
I also discovered why the car always sounded like it need exhaust work at idle... see the sketchy weld at the flex pipe..
 

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#26 · (Edited)
Thanks. I checked just now and the top of the tube is dry, the dipstick is securely seated and the vent cap is loose.
I had already slotted the vent cap previously and made sure it was not all the way down when I replaced it. Are there any other ways to check the vent tube itself other than using something like a piece of hanger wire?
 
#30 · (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, Showbox jiofi.local.html tplinklogin 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.
- 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!
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.
 
#31 ·
Transmission UPDATE.
So after taking some time to think about events, it occurred to me that there were no transmission pan leaks until after I had the fluid changed at my "trusted" lube shop.
So I decided to order up a new pan gasket, a dipstick tube seal and some Ford Mercon V from Rock Auto and change that out. Things went pretty well and I didn't make TOO much of a mess..Having one of those aluminum foil trays is pretty required as far as I'm concerned, especially if the car's on ramps. I was lucky as the one the wife let me have was filled to the brim!!
The old pan gasket looked "okay"...it may have felt a little less supple than the new one, and I'm pretty certain the lube shop just reused it. What I DID find though after cleaning everything and when putting things back together, was that two of the bolts holding the pan had a few stripped threads. I had not even applied any kind of pressure to snug them... I didn't have the ability to tap so I put some blue Threadlocker on the bolts and sent it.
There was a minimal amount of shavings on the magnet and the fluid looked to be in decent shape (let me know your thoughts from the pics on this).
Changing the dipstick tube seal took a few tries. Getting to the bolt (8mm) that secures the tube is a little awkward as the shifter mechanism (floor shifter on this car) is right in the way. Removing the air cleaner assembly gave some extra wiggle room. A u-joint socket adapter and a long extension helps to get to and loosen it. It took me a few tries to get the tube loose. It's much easier to pull from the top of the car, rather than pushing from below. I also didn't realize how far down the tube goes into the pan. Once i had the tube loose, I had to use a pick tool to get the old seal to move then I was able to slide it off. It's much easier to install the new seal into the hole, rather than putting it on the tube first. Getting the tube back in takes a little extra effort and ooomph, but it will eventually go back in. There is a detent in the tube to prevent the seal from going up too far. I'm glad I changed that seal. The one I ordered had a slightly different design (don't know if it was an update) but fit perfectly. I needed approx 6.5 quarts to fill it back up.
Also had a question.. for the vent for the transmission, has anyone ever taken it apart to see what happens inside? There's a video on YouTube where the dude takes it out and replaces it (go to around 3:15), but what he removed just looked like a fitting.. I couldn't see if there was an actual mechanism in the part. I used the straight piece of hanger wire (fits perfectly) to insert in the vent and push, I can feel a little resistance (like a small door or flap), then I push, the wire goes further down then stops (about 4.75 inches)...so I guess the question really is, are leaks (or the lack thereof) the ONLY way to know if that vent is truly working properly? There was no debris or wetness on the wire when I pulled it out and the vent cap and surrounding area was dry, and I've already modded the vent cap with a slot and ensured that it's loose.
Drove around a bit and so far, no leaks, but I have a piece of cardboard under the car that I'll check tomorrow for confirmation!
Unfortunately, I was not able to do the OSS today.

Pics: 6 new photos by Dean Irwin
 
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