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post #1 of 50 (permalink) Old 09-07-2017, 08:11 PM Thread Starter
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High Idle? IAC?

Just want to make sure it is my IAC and nothing else.

My TBird started idling around 1100 rpms and tends to creep up more and more to around 1200 rpms instead of the typical 700-800 rpms that it used to be in normal conditions. I used to have this problem intermittently, where if I shut the car off and turned it back on the problem would correct itself, but now it seems like its stuck doing this high idle thing. I can feel the car trying to move forward when I'm stopped at a light and braking is reduced since the car is trying to move forward lol. Downshifts are slightly more rough since the RPMs are staying up and I can basically accelerate lightly without having to put any input on the pedal.

I'm guessing it's the IAC? Never changed it or cleaned it.
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post #2 of 50 (permalink) Old 09-07-2017, 08:50 PM
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Vacuum leaks are air, right?

Hopefully that's not it, but it's pretty limited.

The only way I know of to check an IAC is to replace it.

A stuck open EGR can cause this as well.

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post #3 of 50 (permalink) Old 09-07-2017, 10:43 PM
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Unplug the IAC Valve and start the car to see if it idles. If it does then the IAC Valve is stuck open. A properly functioning IAC Valve will not let the car run without having to push the throttle.
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post #4 of 50 (permalink) Old 09-07-2017, 10:46 PM
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I had the same issue . mine was also the iac . does it go full throttle fine? If not nay be the tps.
And if its a 94-95 iac I don't think it is as simple to get at like the newer style..
Cel on ?
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post #5 of 50 (permalink) Old 09-08-2017, 06:05 PM Thread Starter
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Originally Posted by 94badbird View Post
I had the same issue . mine was also the iac . does it go full throttle fine? If not nay be the tps.
And if its a 94-95 iac I don't think it is as simple to get at like the newer style..
Cel on ?
My Bird is a 97.

No CEL.

Yeah it goes full throttle and drives fine, really only affects me at low speeds and idling which in turn hurts my fuel economy and makes for a quirky ride, otherwise you couldn't tell. Also worth noting is that it used to happen occasionally last winter when the weather was really cold and a restart fixed the problem most of the time, but then when summer came along it got better, and now it's fall and it's pretty much become permanent now.

I think if it was a vacuum leak I would have other issues like pinging and maybe a code, because a high idle like that would probably have to be a pretty big vac leak that would trigger at least some codes.

I'm going to unplug the IAC and see if it runs.
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post #6 of 50 (permalink) Old 09-10-2017, 03:30 PM Thread Starter
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Here's a video showing the high idle in drive (normal idle should be like 700) and then once you put it in neutral, jumps up to around 1350 rpms and when shifting back into drive at those RPMs it obviously causes a rough transition.
https://youtu.be/e2UuOYsZwMY

I unplugged the IAC and the car wouldn't idle, so not sure if it's still the IAC, maybe it closes but opens too much? Dunno.
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post #7 of 50 (permalink) Old 09-11-2017, 06:00 PM
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When the IAC went out in my 96 4.6 it did not throw a check engine light, or any codes. Mine was the opposite though, and was idling too low to the point it would stall.
On my friends truck it went out and it was doing the same as your car, again no codes.

They are pretty straight forward to replace. A couple of the bolts are in tight location but with a 1/4 ratchet and an extension its a quick job.

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post #8 of 50 (permalink) Old 09-11-2017, 07:43 PM Thread Starter
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Just ordered the Hitachi IAC, once it comes in I'll swap it in and see if it does the trick. Thanks guys, I just wanted to make sure if my suspicion was correct and I think it is...we'll find out.
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post #9 of 50 (permalink) Old 09-14-2017, 05:35 PM Thread Starter
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Alright, Hitachi valve installed today. Just gotta actually start the car and do some driving and idling now when I get the chance.

Here's pics of the old original valve I took off (hence dirtier, blacker) but I noticed some differences inside from the hole I can see the old valve had some sort of spring, new one doesn't. Old valve had a nicer paper/plastic feeling gasket on it, new valve has a plain old paper gasket. Surface finish on the new valve looks worse than the old valve, looks like they run the machining really fast on these leaving all sorts of marks, but not a critical sealing component so it should be just fine. Just some observations. Also can anyone tell me how dirty my IAC valve is? Seems to have a decent layer of deposits on it but nothing I would guess would cause any issue.
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post #10 of 50 (permalink) Old 09-14-2017, 08:45 PM Thread Starter
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Okay now I'm frustrated. The IAC valve made no difference in the idle of the car. Still has the high idle with it creeping up. 1100-1300 RPMs idle in park/neutral and 1000-1050 in drive. Just like in the video I posted. No change.

What to look for now?
New IAC checked off the list.
No CELs
Car runs fine with no pinging or any other signs of a vacuum leak.
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post #11 of 50 (permalink) Old 09-15-2017, 05:30 PM
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What does the vacuum measure at idle?

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
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post #12 of 50 (permalink) Old 09-15-2017, 05:57 PM Thread Starter
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Originally Posted by Grog6 View Post
What does the vacuum measure at idle?
I haven't measured it. But I did a few things: I unplugged the new IAC while the car was running (around a 1500rpm idle when AC is off), and my idle went down to about 500 and became rough. The car still idled. Plugging the IAC back in returned the car to its high idle again.

I unplugged the TPS while the car was high idling and it had no effect on the idle. Still a high idle. Don't know if that means anything.

Any other ideas before I borrow a set of vacuum guages?
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post #13 of 50 (permalink) Old 09-15-2017, 06:00 PM
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You might want to check the condition of the throttle position sensor. It could be worn.

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post #14 of 50 (permalink) Old 09-16-2017, 12:52 AM Thread Starter
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Originally Posted by Draetech09 View Post
You might want to check the condition of the throttle position sensor. It could be worn.
I think that's the next step I will take, I'm gonna return this IAC valve though since that doesn't seem to be the issue at the moment.
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post #15 of 50 (permalink) Old 09-16-2017, 01:43 PM
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Okay now I'm frustrated. The IAC valve made no difference in the idle of the car. Still has the high idle with it creeping up. 1100-1300 RPMs idle in park/neutral and 1000-1050 in drive. Just like in the video I posted. No change.

What to look for now?
New IAC checked off the list.
No CELs
Car runs fine with no pinging or any other signs of a vacuum leak.
Make an iac restrictor plate ...I've had to use one before ..I made it out if thin plastic ..you ate just making the holes smaller to restrict the flow and it lowers rpm and helps hanging idles.
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post #16 of 50 (permalink) Old 09-16-2017, 05:40 PM
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Quote:
Originally Posted by 94badbird View Post
Make an iac restrictor plate ...I've had to use one before ..I made it out if thin plastic ..you ate just making the holes smaller to restrict the flow and it lowers rpm and helps hanging idles.
First I've ever heard of this, let use know how it goes if you try it.

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post #17 of 50 (permalink) Old 09-16-2017, 06:07 PM
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post #18 of 50 (permalink) Old 09-16-2017, 06:50 PM
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To me, something like this is just putting a band aid on it. It's not solving the problem.

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post #19 of 50 (permalink) Old 09-16-2017, 06:59 PM
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That sucks the IAC didn't fix it. It really sounded like the problem. TPS is next, but honestly that is just my guess as well as others; that's throwing more parts at the problem.
Sounds like it might be time to get the voltmeter out and a copy of the factory service manual.

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post #20 of 50 (permalink) Old 09-16-2017, 11:46 PM Thread Starter
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Thanks for the input guys.

So I did some troubleshooting and threw the old IAC back on.

I had unplugged the TPS while the car was running last time and it made no difference in idle. This time I unplugged the TPS before starting the car and surprisingly....regular idle! I then plugged the TPS back in while the car was idling at regular cold idle (950 ish) and a few seconds later the idle shot back up to (1450)!

So I'm now almost certain it's the TPS. I returned the new IAC and put the old one back on since that wasn't the issue.

Ordering a new TPS as we speak, will update once I have the new one on.

Also I'm sure that IAC restrictor is for custom applications such as when you're running forced induction. Because I can see a need for that when there's more air being pushed in through the valve at idle than what is necessary.
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post #21 of 50 (permalink) Old 09-17-2017, 07:21 AM
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Makes sense its the tps...but a lot of times it will cause a no full throttle situation .. It could simply need to be reclocked. You gave to put it in and turn it a bit then bolt it on...you will feel a little tension as you remove the old one..the tps needs be be angled down when put on and turned up a bit till it fits the bolt holes but that bit of tension sets the tps for the proper idle.
If you got a junkyard around you and there's a Ford 4.6..what I did was yank almost every sensor off of it just to have a 2nd one on hand..best 30$ I ever spent ..I got mafs,tps,egr,iac,fpr,coilpacks ect..you make it I grabbed it.
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post #22 of 50 (permalink) Old 09-17-2017, 02:17 PM Thread Starter
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Originally Posted by 94badbird View Post
Makes sense its the tps...but a lot of times it will cause a no full throttle situation .. It could simply need to be reclocked. You gave to put it in and turn it a bit then bolt it on...you will feel a little tension as you remove the old one..the tps needs be be angled down when put on and turned up a bit till it fits the bolt holes but that bit of tension sets the tps for the proper idle.
If you got a junkyard around you and there's a Ford 4.6..what I did was yank almost every sensor off of it just to have a 2nd one on hand..best 30$ I ever spent ..I got mafs,tps,egr,iac,fpr,coilpacks ect..you make it I grabbed it.

Interesting, next time I'll let you know if I need something, but for 37 bucks for a Motorcraft TPS I wasn't too worried with spending on it. Is the TPS spring loaded or does the potentiometer mechanism move freely? I don't want to install it wrong.

Also I did notice that I was hitting WOT much quicker... almost as if 3/4 way of the pedal was WOT....but I'm not sure since I hardly do WOT.
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post #23 of 50 (permalink) Old 09-18-2017, 07:53 AM
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You should go WOT at least once or twice every couple hundred miles. If you never go WOT, you get carbon build up, then pinging, then there's a new thread on here.

I like to put it in manual 2nd and punch it from 20 MPH to 60 or 70 MPH, that is a good long blast.

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post #24 of 50 (permalink) Old 09-18-2017, 05:30 PM
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When your new TPS is installed, use some safety pins to probe the connector and measure the "idle voltage" with the key on engine off. Ideally you want this set at .96v but >.89v and <1v will be fine. You can loosen the mounting screws and get a slight adjustment before torquing them real tight. Some guys even oval out the holes for better adjustment but I would not suggest that before checking for a throttle plate idles stop screw-



However, I still think , as suggested above, you should hook a vacuum gauge up and shoot a video of what it does at idle and what it does with a sharp throttle blip.

Another item not considered yet is the coolant temp sensor. Some Ford use 2 of these, one for the gauges and one for the PCM, which is the one I suspect could be your issue.
Curious what the TPS does for you though, as, it also has a lot to do with transmission function.

Hope this helps.

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post #25 of 50 (permalink) Old 09-18-2017, 05:43 PM Thread Starter
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When your new TPS is installed, use some safety pins to probe the connector and measure the "idle voltage" with the key on engine off. Ideally you want this set at .96v but >.89v and <1v will be fine. You can loosen the mounting screws and get a slight adjustment before torquing them real tight. Some guys even oval out the holes for better adjustment but I would not suggest that before checking for a throttle plate idles stop screw-



However, I still think , as suggested above, you should hook a vacuum gauge up and shoot a video of what it does at idle and what it does with a sharp throttle blip.

Another item not considered yet is the coolant temp sensor. Some Ford use 2 of these, one for the gauges and one for the PCM, which is the one I suspect could be your issue.
Curious what the TPS does for you though, as, it also has a lot to do with transmission function.

Hope this helps.

There are three pins. Which pins should I probe?

What's the TPS relearn procedure? Is there one because I know many other cars do have one. I have the battery unplugged now for a few minutes because I put the new TPS on and started the car without any relearn and my high idle was still there.

My coolant temps do occasionally shoot up to the upper 2/3rd mark....could be it. Too see attached picture of an earlier drive.
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post #26 of 50 (permalink) Old 09-18-2017, 05:44 PM
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97 high idle
TPS was the problem. I thought it good to link this thread in for the nest guy who might be searching

http://forums.tccoa.com/7-engine-4-6...64k-miles.html

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post #27 of 50 (permalink) Old 09-18-2017, 05:48 PM Thread Starter
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97 high idle
TPS was the problem. I thought it good to link this thread in for the nest guy who might be searching

http://forums.tccoa.com/7-engine-4-6...64k-miles.html
Yes, I checked that thread and it kind of helped me believe it was the TPS. Can you look at my above reply?
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post #28 of 50 (permalink) Old 09-18-2017, 08:54 PM
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I never had any of my mn12s any engine any mods ever run that hot...if I was beating them in 100 degree weather I was lucky to get them up half way..
Time for cooling system and rad flush..possibly the water pump fins are worn causing poor circulation..
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post #29 of 50 (permalink) Old 09-19-2017, 12:30 AM Thread Starter
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SOLUTION: It was TPS. The TPS needs to be reset or relearned after installation. I just unplugged the battery, turned the light switch on for a few seconds, and let it sit unplugged for a few hours (probably really only need a few minutes)... typical ECU reset procedure. Then I plugged the battery back in and started her up. Regular cold idle and warm idle at approximately 850-900 rpms. AC on, same RPMs if not a bit less. I'm confident it's solved. But I haven't driven it, just started it but the idle issue is corrected.


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I never had
any of my mn12s any engine any mods ever run that hot...if I was beating them in 100 degree weather I was lucky to get them up half way..
Time for cooling system and rad flush..possibly the water pump fins are worn causing poor circulation..
I live in Vegas 100+ degrees at night in the summer. But I have seen that temp go up during nicer 80* days too. Coolant was drained and refilled. But it does it rarely, I'm attributing it to a sticky or bad thermostat. I have a new 195* SuperStat thermostat and o-ring that I plan to install but hardly get the time with college and what not. I feel like the car's temps creep up more in idle than in driving, I also feel like the fan kicks on a lot later than I'd like when idling (gauge climbing higher than 2/3) before it decides to finally start moving air. Driving at 45 brings the temps back down to around halfway on the gauge. Since I'm still planning on supercharging it I was going to consider radiator fan upgrades or radiator upgrades. Also put a trans cooler and take the trans heat load off the maain radiator. So this occasional temp thing is kinda on the back burner. But it'd be nice to know if my water pump and sensors are up to snuff.
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post #30 of 50 (permalink) Old 09-22-2017, 03:54 PM Thread Starter
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Finally drove it today. Woooooooo, so much nicer to drive, feels much quicker and less lethargic, hauls ass, shifts so much nicer. Man, I put this off way longer than I should have. I had lost the ability to do my one wheel peels and now I have that back as well. Fantastic.
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