In gear, I release the gas pedal but the RPMs do not decrease

Tiny
DAVID JIMENEZ2
  • MEMBER
  • 2003 FORD TAURUS
  • 3.0L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 200,000 MILES
The original problem was a rough idle/stall. I replaced the IAC with little to no effect and then found a massive vacuum leak at the PCV valve end of the hose (hard plastic tube is in between the two rubber ends). I removed and replaced the PCV valve and valve-side hose section and that helped but did not completely fix the rough idle, so I ignorantly adjusted the throttle stop screw so the car would run.

Zoom to this year. My daughter told me that the car had no heat (heater core was clogged again) and has a rough idle again, and it wants go all by itself when she is not pressing the gas! While looking under the hood for clues to this problem, I found the leak that I could not find last year on the other end of the PCV elbow hose at the intake manifold. After I removed and replace the entire hose assembly, the car starts and idles better than ever, but a bit high. So I adjusted the throttle stop screw to hopefully where it was before I messed with it. Doubtful I got it right, but I reset the ECM each time I adjusted to clear the learned settings just in case.

So then I tested to see if this was causing her acceleration issue, but it did not have any effect.

Symptoms:
When in drive, I get up to speed and release the gas pedal but the rpm's do not decrease. Car eventually slows down, but only after quite a while. I can travel miles at forty five mph without touching the gas. This is true if I use the cruise control or not. If I apply the brakes, it will slow down, but it is like the gas pedal is still being pressed down. When I place the transmission in neutral, the rpms go up. This only happens when in gear. When I come to a stop, I have to brake until it shifts to first gear, then it settles down to a manageable rpm. It idles at 750 rpms at a stop. But once I take my foot off the brake, rpms will slowly climb up to 1500 rpms shifting into the next gears. I also noticed that while accelerating up to fifty five to sixty mph, there is sometimes a "rough" spot around forty five to fifty mph where the car sometimes loses power or shudders very briefly and feels like I ran out of gas or is trying to shift gears, but then just as quickly, it recovers. I also must add that whenever the climate control switch is placed in any position clockwise of the center off position (floor and dash, floor, WinDefr and floor, WinDefr, respectively), or in the two AC settings, the rpms spike up to 1500 rpms and the AC clutch engages. This does not happen when using the dash vent position. I thought that the clutch should only engage when set to AC/MAX AC or the two defrost positions, but maybe that is how Ford does it. In any case, the spike in rpm cause the vehicle to suddenly lurch if in any forward or reverse gears. There are no codes being thrown by the computer.

What I have tried:
I have tried pulling up on the pedal from under it to see if the pedal is sticking, but no effect. I have inspected the throttle and cruise control cables/linkage, and there is no issue there. I have sprayed a whole can of starting fluid all over the vacuum hoses and fittings and have not found a single change in rpm. I have cleaned the throttle body no effect. The car did not have a "check engine light" for the TPS, but I replaced it anyway -no effect. Removed and replaced the Idle air control (again), no effect.

Any advice would be appreciated!​
Do you
have the same problem?
Yes
No
Wednesday, January 4th, 2017 AT 8:10 PM

25 Replies

Tiny
STEVE W.
  • EXPERT
Disconnect the battery cables and short them together, that will clear all learned data from the ECM.

Then try a test, Disconnect the IAC and see if the idle drops.

If it idles down and the throttle responds when you pull the IAC connector off, verify that you have the correct IAC valve, there are a couple out there that are supposed to be correct but actually are the wrong part. One with a brass insert and spring and one with no insert. You want the one without the insert.
Was this
answer
helpful?
Yes
No
+4
Wednesday, January 4th, 2017 AT 11:10 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
Thanks! Will try the battery leads shorting step today after work. That is a really good idea, wish I thought of that! With the IAC valve, what part is brass? The plunger, the cup? Or better yet where on the IAC is the insert located?
Was this
answer
helpful?
Yes
No
Thursday, January 5th, 2017 AT 11:57 AM
Tiny
STEVE W.
  • EXPERT
The brass insert is inside the valve opening. The issue is that there are two 3 liter engines, used and the valves will physically interchange. Then there are two different designs of one of the valves as well.
Was this
answer
helpful?
Yes
No
+1
Thursday, January 5th, 2017 AT 6:45 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
After pulling and shorting battery cables there is better idle, less frequent hunting of rpm in Park and gear with brake applied and doesn't go so high as before when turning on the climate control, but the sticky accelerator issue is still there. Just not as pronounced. If I unplug the IAC the idle drops a little bit with no climate control on and in Park, and with it on it almost dies when the AC clutch kicks in every ten seconds or so. But when I drive down the road with it unplugged, the sticky throttle problem goes away entirely. I have checked the IAC and it is not a brass model, and the spare I purchased is a brass model and when I plug the brass one in, the rpm goes nuts, so I am guessing it is the one for the other engine? The original IAC was thrown out last year so the one I have been running on is supposedly the correct one? I noticed the brass one has a stamped Roman numeral I stamped inside the chamber and the one without the brass insert has a Roman numeral II. You mention there are two different valve designs? How can I tell which one is for this car? I am tempted to adust the idle manually and leave the IAC unplugged. Thanks so much for your help. Do you have any further suggestions/guidance?
Was this
answer
helpful?
Yes
No
Thursday, January 5th, 2017 AT 7:33 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
Here is a side by side comparison after cleaning the one without the brass.
Was this
answer
helpful?
Yes
No
Thursday, January 5th, 2017 AT 8:04 PM
Tiny
STEVE W.
  • EXPERT
There is the problem; Both of those are the other design with the spring loaded valve.
This is what it should look like. Notice no spring or bushing. Ford # 1F1E-9F715BA

When it is at idle that valve stays really close to closed with the ECM sending a pulsed signal to it to open it sort of like this (Closed = _ open = ) __ __ __ __ __ __ ). The more "open" pulses the more air the valve lets in and the idle goes up.
In your case the spring is holding the valve open and the ECM still pulses the valve once you let off but with the spring there the valve isn't actually closing until the constant pulse from the ECM sort of hammers the valve closed.

I would be very tempted to visit the parts store, buy a new one, open the box to verify it is correct, bring it home. Then take a pair of needle nose pliers and remove the spring on the current valve, put it back on and see if the sticky throttle goes away. I am betting it does. Then return the new part for a refund.

Once you get the valve fixed, reset the idle to correct spec and you should be good.

Then you can be like the rest of the mechanics in the world when you discover that the "right part" is sometimes the wrong part, thanks to a minor revision, or an "improved" part that is not.
Was this
answer
helpful?
Yes
No
+2
Thursday, January 5th, 2017 AT 9:00 PM
Tiny
STEVE W.
  • EXPERT
Oh, forgot the heater core issue. A way to fix that is to clamp off the heater lines, remove them, flush the core both ways, then install a coolant filter in the line that sends coolant to the heater. There are a few out there. I like the cheap way myself. Get a set of solid brass garden hose ends (male and female) in 1/2" or 5/8" (to match the heater hose size) and a few of the filter screens like you put in a pressure washer hose. Add those to the line with a couple good clamps. They will catch the larger crud that likes to block the core. For folks who want the ready made version google
RF002 - Universal Heater Core Coolant Filter Set

Or you can get the "fancy" version from these folks.
http://www.ganofilters.com/

One other option I did on another vehicle is to install the fittings in both lines. (one set reversed from the other) This allows the option of bypassing the core if it starts leaking and you can easily flush the core or cooling system in both directions with a garden hose.
Was this
answer
helpful?
Yes
No
+1
Thursday, January 5th, 2017 AT 10:10 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
Steve, where the heck were you last year when I started this mess! You have been incredibly helpful in my quest to fix this car. I have literally put over eighty man hours the last two weeks chasing this problem, not counting the time from last year, countless visits to the "parts" store, and mom and pop mechanic shops. I have the part on the way this time I am cutting my losses and ordering directly from the local Ford dealership. (Actually I am adding to my $$ losses, but saving myself further heartache and time visiting all the parts stores in search of this elusive part).

As far as the heater core flush/filter install goes, I will have to look into that. I would have to take it to a friend's garage (with heat and running water and a drain) to do that, I think I would do your method of just buying the parts instead of the "kit". This car seems to get that core plugged issue, something must be rotting away internally to plug it up so badly, so quickly after a flush (second time in two years). One possibility for the low heat issue could be a fresh air mixer/vent damper not closing/opening fully when in the max heat position (so i'm told by the guy who flushed the core last time). Do you know how to troubleshoot this so I can eliminate it from the possibility. I just had the thermostat replaced on last Friday (no effect), and the core flushed on Monday worked better-ish for a day, and then low heat issue came back a day later.

Thanks again, and I will post the results on the IAC later today.
Was this
answer
helpful?
Yes
No
Friday, January 6th, 2017 AT 9:28 AM
Tiny
STEVE W.
  • EXPERT
When you do the flush, do it in the reverse of the way the water flows through it. I made a core flushing machine because I got really fed up with heater cores.

For the blend door, you remove the lower trim panel (behind the dash, passenger side foot well) Blend door and actuator is right there. To get the upper bolts easier you can pop the glove box out.
Sort of like this....
https://www.youtube.com/watch?v=xK7rP49gfio

Note the time when he says to watch this part as it will fall down. That lever connects to the blend door. If you watch that while moving the temp button it will tell you if the door is closing.
Was this
answer
helpful?
Yes
No
+1
Friday, January 6th, 2017 AT 12:36 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
The new OEM IAC works great! Just need back off the throttle stop screw a little bit (it's nearly flush now, as the deceleration is still a little too sluggish for my likes.
Was this
answer
helpful?
Yes
No
Friday, January 6th, 2017 AT 9:59 PM
Tiny
STEVE W.
  • EXPERT
Do another battery cable ECM reset with the new valve. It will need to re-learn the idle characteristics of the new valve.
Was this
answer
helpful?
Yes
No
+1
Friday, January 6th, 2017 AT 10:57 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
I did that when I installed the new IAC. I now do that every time I change a component. I read somewhere that the throttle stop screw should be set fully backed off and then given one full turn clockwise, mine is set at 2 or 3 full turns.
Was this
answer
helpful?
Yes
No
Saturday, January 7th, 2017 AT 8:51 AM
Tiny
DAVID JIMENEZ2
  • MEMBER
Everything is running just fine now. Time to give it back to my daughter. This was quite the learning experience! Thanks again, Steve!
Was this
answer
helpful?
Yes
No
Monday, January 9th, 2017 AT 8:10 PM
Tiny
STEVE W.
  • EXPERT
Remind her that the next repair is her job. (Yeah right, like a dad is going to do that).

Glad you got it all sorted out. You're very welcome. Thank you for using 2CarPros. Com Please return with any auto related questions, we're here to help.
Was this
answer
helpful?
Yes
No
+1
Monday, January 9th, 2017 AT 9:43 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
OK, So maybe I spoke too soon. The idle is fine, but when I take my foot off the gas when in gear going down the road, the car still doesn't slow down immediately like it should. It does start to slow down, but it really takes its time. I have a scan tool hooked up and am looking at the TPS reading and it goes back to 16.1% (closed throttle) when I let off the gas. There is no dead spots and it seems to read smoothly throughout the travel. I checked at parked idle closed throttle and it reads 16.1%. Is this normal? Shouldn't it read closer to 0%, as I have the throttle stop screw backed almost entirely out of the threads. I understand that when I put the TPS on, I have to tilt it into position and back down again so that the lobes mesh properly, so there may be a greater than 0% reading due to that. I just thought the ECM would adjust for that after an ECM reset and display a "corrected" % reading to show a more usable reading to the scan tool, but maybe not. Any ideas? I can't seem to find any other vacuum leaks that may cause the excessively slow return to closed throttle speeds. Thanks!
Was this
answer
helpful?
Yes
No
Wednesday, January 25th, 2017 AT 3:38 PM
Tiny
STEVE W.
  • EXPERT
TPS should read lower than 16% at idle. Sounds like it's a bit out of adjustment.
You won't see 0% because the sensor always passes some voltage even at fully closed throttle but 5% or so is about normal with a vehicle that has an IAC valve.

Here is a question. If you head down the road, let off the throttle and it doesn't slow much, shift into neutral. What do the rpms read and do they rise at all when you shift to neutral?
Was this
answer
helpful?
Yes
No
+1
Wednesday, January 25th, 2017 AT 6:30 PM
Tiny
DAVID JIMENEZ2
  • MEMBER
Steve, when I shift to neutral the RPMs pretty much stay the same immediately after throttle release, then begin to gradually drop slowly a few hundred RPMs, then they shoot back up for a couple-3 seconds before beginning the slow downward trend again as the car slows.
Was this
answer
helpful?
Yes
No
Thursday, January 26th, 2017 AT 9:27 AM
Tiny
DAVID JIMENEZ2
  • MEMBER
Ok, so I paid more attention to the "shift-to-neutral-while-in-gear-going-down-the-road-with-foot-off-the-gas-scenario". The RPMs actually do shoot up a 100-150 RPM immediately after shifting to neutral. This only happens when in the higher gears, though. When in first gear it is not evident -it is more responsive when in first gear. So on the way home I picked up a new TPS and tested it against the old one. The new one actually reads 18% throttle at idle vs the 16.1% on the old one. I went ahead and unplugged the IAC to see if it had any effect at idle, and it didn't have any effect until the load increased when the compressor turned on -then the engine started to stumble and run rough. I plugged it back in and then the idle got smooth again. I give up. I have absolutely no idea what to do next!
Was this
answer
helpful?
Yes
No
Friday, January 27th, 2017 AT 5:26 AM
Tiny
STEVE W.
  • EXPERT
OK, forgot to ask this. If you are setting still, trans in park. What does the engine do if you hit the gas and let off? Does it drop right back to idle? Now if you drive it and shift down one gear (out of overdrive) does it slow down better?

There was an issue on 97-2000 Taurus models where they didn't engine brake at all and would coast for a long time. In that case you could get the PCM reprogrammed by a dealer to change that. I thought they eliminated this after a lot of complaints but it might be an idea to ask a dealer about it. I cannot find anything in OASIS but there are things that are left out.
Was this
answer
helpful?
Yes
No
Friday, January 27th, 2017 AT 8:29 AM
Tiny
DAVID JIMENEZ2
  • MEMBER
If in park pressing and releasing the gas has normal effect on RPMs. The RPMs drop immediately like a normal car does. It's only happening when in forward gears (reverse is kinda fast too, though now that I think about it). I'll check on the way home today to see if there is a difference when I have it out of Overdrive.
Was this
answer
helpful?
Yes
No
Friday, January 27th, 2017 AT 12:55 PM

Please login or register to post a reply.

Recommended Guides