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87 Mustang GT 5.0. Basically stock besides exhaust and some wheels.
I've got a very annoying idle.

This UPandDOWN - hunting idle happens after I may crank my car in the mornings and when the engine is trying to warm or even when my engine is very warm. Either way.

After it idles up and down for a few seconds, it will basically straighten out and go to a smooth idle. But when it DOES idle bad, it goes to a VERY low idle to a regular idle.....back down to a very low idle, back to normal. Back and forth.

Before you give answers, here's what I've done.

- I HAVE checked the TPS sensor and it has checked out OK.
- I HAVE put it on a diagnostics machine (two different ones) and they both checked out OK.
- I HAVE put a new IAC sensor on and that didn't help it any at all.
- I went back and had my buddy (best mechanic in town) and he looked at it and said some vaccuum lines were corroded. So I took those off, and surely enough, they were, replaced them, and it worked great for a few hours. Then back to the normal rough idle.
- I (as of yesterday) replaced the 02 senors and that seemed to have helped it out a bunch.
- I'm sure there are a few more things I've done but I can't figure it out anymore. Sense the 02 sensors were put on yesterday, it's ran GREAT. But now it's just starting back again.
I've gone ALmost 24 hours without it, then it seems to be starting back again today. It's only done it once, but the point is. it's doing it.

Can someone please help me?!?! post a reply on here, but also email it to me at [email protected]
 

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Try cleaning your battery cables and terminals.

If that doesn't do it, I'd try tuning her up, if it's been a while.
 

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Discussion Starter #3
Terminals and cables are in tip top shape.

Car is tuned up.

I am going to try the LAST thing on my list.
And that is to replace the Thermactor Air Bypass & Diverter.
I've read up on this component making the cars die. Mine hasn't
died yet but I hope this will clear it up. Has to do with all the smog-crap.
Why can't we just get in our cars and romp. Freaken EPA...
 

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Does it turns off sometimes while is idleing bad? If it does mine does the same. So if you find a fix, please post it, so I can fix it as well. Good luck.
 

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You can test your TAB and TAD. Apply voltage from a 9-12 volt battery to each one. It should flow air. Unhook the battery power, and they should close, and not allow airflow.
 

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Discussion Starter #6
OK. I will.

I was planning on just buying one and replacing it, but apparently not one local part stores carries that part. They said it's one I'm going to have to get from Ford themselves.

How in the heck am I suppose to apply voltage from a 9v battery to them. Can you give me a more detailed description of this process?

Tonight I ran the car without the wires hooked into the TAB and TAD. There wasn't really a difference in the performance of the car.

Any ideas?
 

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I removed them from the car. A nine volt battery and some speaker wire ought to work. If you have female spade connectors on the wire, that will make it much easier to connect to the solenoids. It's been a while since I messed with those, but the terminals on the 9 volt battery might just line up with the lugs on the solenoids. Definitely helps to have them out of the car. Sometimes they clog up too.
My guess, though, is that the idle problem isn't caused by either of those solenoids. I'd go back and check the vacuum lines again. Make sure that all the ports under the upper intake are either connected to accessories, or capped. The one going to the MAP is especially crucial. Also, try pulling off, and capping the line which goes to the charcoal cannister. See if that makes a difference.
 

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haunting idle

Guys. I have had similiar problem with surging idle.I have replaced the IAC,ECT I have reset idle and IAC several times but still have problem..Engine starts and runs perfect until it goes to closed loop and then surging occurs and vehicle dies, start again and surges and stalls, start third time and surging starts to improve and as it warms runs fairly smooth..I ran codes and keep getting IAC malfunction, even with the new IAC..I disconnected the IAC when engine was cold and disconnected neg. cable.. Reattached neg. cable and turned idle adj. screw 1 full turn, started engine and it did not surge or stall until i shut it off and restarted..Then it surged but did not stall and smoothed out after 30 seconds..(I realize that surging will be normal with a disconnected IAC after running and warm-up, because its function is to add air and help the Ecu initially balance a/f ratio) But I am at a loss as to how to repair IAC malfunction code..Also have a newer ACT..I did do a mass air conversion, and thats when the problem started.I retained the newer MAP sensor and removed and blocked the hose, but left unit pluged in per instructions..If anyone has this problem with IAC malfunction code please advise as to fix. Any data greatly appreciated!! Thanks: AL
 

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check your fuel pumps and filters....
fuel pressure regulators are starting to fail tehse cars are 14+ years old now the regulators go out and you could have 100 psi or 12 psi and this throws the idle WAY off....
if not sounds like a vacuum leak somewhere for all of you
 

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I once had a vacuum line that kept splitting and causing funky idle on me.

It was on the firewall, the one that runs to the AC system. When the air flow location selector stoped working, my idle went a bit hairy.

Might want to re-check your lines for any new breaks.

If the 02 sensors helped it, you might have had them gunked up from runnign too rich... could be a MAF problem or a Fuel Pressure problem. Then, the IAC constantly huting to find a good idle causes the surge.

Here is a thought. You replaces the sensor, but did you use any intake cleaner on the TB or the passages incase there is any gunk in there blocking or restricting air flow?
 

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Idle setting

Have you tried setting the idle the ford way? I've had problems with my car idling but this helped, I still have some other issues I need to work out.

-Get the motor to operating temp
-Unhook the IAC and set the idle using the throttle body adjustment, if the motors stalls turn the adjustment screw in one turn and restart it, get the idle where you want it
-Then set the TPS .96-.98 volts
-Shut the motor off
-Unhook the Negitive battery cable for 15-20 minutes
-Plug the IAC back in and reconnect the battery
 
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