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Discussion Starter #1
It just makes no sense whatsoever. Today, I went out to try to work on this idle problem I've had ever since installing a set of LT's (the O2s are in a primary, so I doubt this is the problem)a little more, convinced that I had a vacuum leak. Well, I found that two of the holes in the passenger side vacuum tree (for the emissions stuff, which I no longer have), weren't plugged, so that was an obvious vacuum leak. I plugged those, figuring maybe it would help. Started it up....no change....not one bit.

Here's the deal, the car surges seemingly all the time. Warm, cold, accessories on or not....doesn't matter. It surges like crazy. It SEEMS to get better when the car is warmed up, to the point that at a light, it will idle pretty steady for 5 or 6 seconds. But then the idle starts rolling, and gets worse, and worse until sometimes it will die.

I've tried everything, and I do mean EVERYthing that I know of, including all the usual tricks....10-pins, check TPS, reset the idle, fiddle with the fuel pressure,yadda yadda yadda. I can't get it to quit! Today was the last straw, though. I was out driving, and the car got good and warm. I get home, got out for a minute and left the car running. It idled PERFECTLY for about 15 minutes straight, so I'm thinking maybe it's fixed, and shut it off. 20 minutes later, I come back out to put it in the garage, and it surges like hell again!! WTF!! %()(*)#())@(!!!!

:livid: :livid: :curses: :curses:

Sorry this is so long, and my apologies for yet another idle quality thread, but I have no clue what's going on anymore, or what to do. Does ANYone have ANY kind of ideas?
 

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If I were you I'd unplug the battery to clear the adaptive memory because even though the EEC is open-loop at idle its lookup tables are influenced by the adaptive memory from closed-loop operation and that vacuum leak may be causing corrections that lead to idle problems.

Also, what's your timing set at? The EEC uses advance control to help with idle regulation but in my experience if you advance it too far you hurt its ability to do that, and it'll surge.

Worse comes to worst, get an idle air adjuster :D
 

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Discussion Starter #3
MFE said:
If I were you I'd unplug the battery to clear the adaptive memory because even though the EEC is open-loop at idle its lookup tables are influenced by the adaptive memory from closed-loop operation and that vacuum leak may be causing corrections that lead to idle problems.

Also, what's your timing set at? The EEC uses advance control to help with idle regulation but in my experience if you advance it too far you hurt its ability to do that, and it'll surge.

Worse comes to worst, get an idle air adjuster :D
I tried clearing the computer (multiple times), and the vacuum leak is fixed, but I guess I can try the computer again.

Timing is set to 18* BTDC.....and that's after backing it off a few degrees. Of course, aluminum heads like timing, but I suppose I could back it off a little further if it would improve the idle.
 

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Seems to be related to the 02's as that is the only thing you changed ?? Have you considered the i.a.t senser ??
 

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IAT intake air temp.. On yours I think its on the inlet guessing on # 5?.But I still can't get around this starting to happen when you changed to long tubes.Sure there are less pulses but it should work when warm.It may come right after a few miles...Or loose connection on the 02's ????
 

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Discussion Starter #8
Ahhh....I got ya. AKA the ACT sensor. Haven't checked that, but I haven't pulled codes recently, either, because I can't keep it running long enough to do it.

I don't think the connections to the O2s are loosed, but I won't rule out the possibility. Guess I'll have to get under there and check sometime soon. But with the O2s being located in a primary on these headers, I wouldn't think pulses would be an issue. I dunno....
 

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Discussion Starter #9
Here's another thing I forgot to mention. I went to fiddle with the fuel pressure, which of course entails removing the vacuum hose from the FP regulator. Soon as I did that, and plugged the hose with my thumb, the idle picked up about 75-100rpm, and leveled out. Could this be a clue?
 

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Hmm...sounds like the diaphragm in the FPR might be leaking vacuum?
 

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Discussion Starter #11
Hmmm....now there's a possibility. Got an easy way to test that?


Man, I need to get a vacuum gauge and see what the heck is going on at idle. Anyhow, thanks for the ideas on this, Frasier.
 

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No, I don't recall how to test it but I do recall someone tracking down a FP fluctuation problem a while back that turned out to be a similar or same problem and he was given advice on how to test for it, so you may be able to find it with some digging.
 

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Drive it with the vacuum disconnected and plugged for awhile and get it warm, see how it idles, then let it completely cool and crank it and see how it does. You could test it that way. I have friends who run there stangs with no vacuum all the time. Doesn't seem to hurt'em , but you might lose a little power or mileage.
 

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do you have any fuel in the vac hose from the regulator? If the diaphragm was broke you would most likely fuel going through the hose. You can also try sucking on the vac hose (with the car off of course;) ) if it feels like you can suck air through it that would tell ya its bad.

-Billy
 

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Yep,Billy's right .
Seen it many times.
Also ,I hate to sound like a
broken record but how old is
that IAC motor ????
Rip that puppy off & clean out
all the passages of coked
on carbin.Also check your throttle
body for the same .
Hope this helps

Sickman :joy: :joy: :joy: :joy: :joy: :joy:
 

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Discussion Starter #16
Nope....no fuel in the vacuum line to the regulator, which kinda confuses me. But I haven't tried the other methods. I'll give those a try when I can.

The IAC is factory, but it's definitely clean. I could test the resistance, if someone has a reference value as to what it SHOULD be.
 

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Man I know what you are going through I spent a small fortune replaceing parts and trying to fix my idle. I changed everything and it would still surge. What finally fixed mine was I unbolted the bracket that holds down the maf meter and twisted the top of it so it faced the motor the car surged like crazy, I then twisted it 180* so that the top now faced the fenderwell. I can't make the car surge now. All the money I spent and something free fixed it. I am not saying that is what is wrong with yours but it is free and worth a shot before you spend any more money or pull any more hair out. Good luck and God bless.

Keith
 

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Discussion Starter #18
That's one thing I haven't tried....clocking the MAF. One more thing I can try when I get a chance.....thanks.
 

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Hey - Is the ACT sensor - the same as the water temp sensor? I put a new water temp gauge and used this spot. Will that effect the computer at all?
 

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Jim,

ACT = Air Charge Temperature. The hole for the ACT sensor is not a coolant passage. If you hooked your water temp gauge to the ACT, your reading the air temp, not water temp. If you removed the ACT sensor, it will effect your computer - I don't know how much.

Pete
 
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