Idle all over the place

[Digger]

OK, I've got a 96 GT Convertable, 5spd, mostly stock as far as I know. With the AC off, the idle goes from about 800 to nearly 2000, back to about 1200 and sometimes will settle around 900. What's the deal here? I replaced the TP sensor-no help. With the AC on, this happens all the time. With the Flowmasters, it makes it very noticable, almost embarasing.
What can I do to correct this?
TIA

 

[Dan_Soprano]

IAC valve.

 

[Dan_Soprano]

 

[Digger]

I'll give it a shot.
Thanks

 

[chini42]

Mine does this too, but I have a theory. When you get a chance, start your car and let it idle for 15min, before you drive it/move it or even press on the gas. If I do this, mine will not search for an idle, but if I just start it up and start driving, the idle will be all over the place. I hooked up the Star tester, and I get an ignition misfire code, but only in a low number (not enough for a MIL) Everytime the searching idle comes, a new misfire code comes along with it. If I let it warm up, there is no misfire code and no idle problems. Im thinking that if the EEC sees a misfire code, that it sends it into a sort of limp mode for some reason. It's just a theory, but so far it seems to work, cause I can get it to idle fine anytime I try and there are no new misfire codes when I let it warm up to 180, before I drive it.

Chris

 

[Mike97gt]

it only does it with the a/c on?

How well does the a/c work? does the clutch cycle often..

if it does you have a low a/c charge, what happens is the a/c system is cycling so rapidly that the pcm does not get a chance to compensate for the load, so it overshoots then idle.

you will see the rpm's jump up and down only with the a/c on or in the defrost/mix position. if you start the car with the a/c off ( sometimes when you turn your a/c off the clucth still cycles for a few minutes) the idle should be steady.


remember the a/c activates any time you use the defrost or mix pos. if the weather is cold enough.

 

[Digger]

The AC can be described as iffy at best, but hey, its a convertable! Seriously though, I knew it cam on in the Mix position, and that is where I normally keep it, but it just seems to take such drastic swings, even with the heater controls off. I'm going to get the IAC today and give that a try.

 

[Don 95Vert]

There is an idle speed adder for AC in the PCM - shouldn't do what you describe though. First thing I'd do is look for vacuum leaks or leaks in the intake tube after the MAF. Then I'd run codes. Then I'd probably clean the IAC valvle with carb cleaner and I'd also use some 'coated TB safe' spray cleaner to clean the inside of the TB and blade - you can also use a soft brush with the spray to clean carbon off. Monkeying with the TB stop screw can also do this - it has to be stock.

Don

 

[Mike97gt]

The AC can be described as iffy at best, but hey, its a convertable! Seriously though, I knew it cam on in the Mix position, and that is where I normally keep it, but it just seems to take such drastic swings, even with the heater controls off. I'm going to get the IAC today and give that a try.

I am still leaning toward the a/c being low on freeon and or a bad CCRM leaving the compressor cycling. if the IAC you bought don't fix it check out what I am saying. I have had several CCRM a/c controled fords do this exact problem you are talking about and it was related to the a/c

try pulling the electrical plug off the compressor , or pull the electrical connector off the low side and high side switches and then run the car. trust me just try it, just make sure the compressor is not cycling then if it's not then check the IAC.. and if your a/c compressor is running even in the off pos. you have a CCRM problem.

When you post a EEC problem on here about my tech help and see what they say, I may tell you to check out some strange stuff but there is a reason for it.

that reason is I have had a problem car in my bay ( I am a ford tech by trade) that had a similar problem and I think that maybe the problem with yours.

 

[Digger]

Thanks again. I give that a try too.

 

[Mike97gt]

ok please update when you try it.

 

[Digger]

Well, the new IAC seemed to do the trick, with the AC off. I also did the copper cap thing, that's AWESOME.
Next step I guess is to get the AC properly charged and go from there. Thanks for everyones help.