Ok, I've about had it with this

[99FiveOh]

When I did the engine swap I converted to all fox throttle body parts. Since the car has the exact same behavior now as it did before the swap I can rule out the IAC and any of the parts associated with the Tbody swap.

Before the swap though, I could leave the car sitting in the yard idling and it would start hunting on it's own and eventually die. It would do this in drive throughs which was very annoying. The problem was cured with the new setup.

Cold start-ups are fine for the most parts. Except for instance, if I pull the car to the back yard to work on it right after a cold start, it will hunt and die upon upon stopping. So I have to ease the gas pedal a little bit to compensate. What is seams like here is the computer is letting the RPM's fall way too low when the car comes to a stop then it tries to over compensate high, the overcompensates too low which results in a stall.

In the fox's I've owned, as I come to a stop, the RPM's don't just fall to idle instantly, it kinds tapers down gradually over a couple seconds from around 1000 rpms down to idle. That's what this car should do. And yes, my car seems to do it more severely with the A/C on.

 

[94stangfan]

Have you checked the surging idle checklist?

I am surprised that this hasn't been posted before as it is what I used to get thru my idle problems...

In my 86 I had this exact problem... I had to change my Ignition control module, clean the EGR valve (it was stuck), and clean the throttle body. I also replaced the IAC motor but I don't think that was bad as I gave it to my neighbor and he is using it without problems.

For what it is worth, my throttle body didn't look dirty. But as soon as I cleaned it. I had no more problems.

I know mine is an 86, but I believe they are very similar and could have the same issues.

Hope this helps,

Keith

 

[99FiveOh]

I just did a major engine swap on this car. While everything was apart I made sure every single part I put back was either brand new or in brand new condition. Trust me, as far as the parts are concerned, I know they are good.

The EGR valve is gone, the throttle body is whistle clean, the IAC is a brand new unit that I sourced a while back. If there was any question in my mind about the condition of my parts I wouldn't have even posted this thread. This is where I am at the end of my rope because I know it has something to do with the tune. I'll bet if I put the stock intake back on, stock headers, stock air box, stock mufflers and catted H pipe as well as the EGR and smog pump the car would probably run perfectly. These computers in these cars don't like mods and if I want to have my mods I either have to get a tune or live with the BS!

 

[99FiveOh]

Ok, I did the procedure in this post here: http://www.stangnet.com/mustang-for...laggin-spuuter-problems-help.html#post8237206

And I found that my blade stop screw was not engaging the stop enough. So I fixed that issue and it helped considerably but the car still hunts after a warm start up. Only now, it doesn't stall every time like before.

One thing to note is that when the CE light does finally come on, the car settles into a rock solid idle. I tested this about 5 times by shutting the car off and watching the idle go crazy until the the second the light comes on then the crazy idle stops.

So, what exactly happens when the CE light comes on that would fix the idle issue? Is it going into limp home mode? All my smog and egr stuff is deleted, is that enough to cause all these idle issues?

 

[Bullitt95]

All my smog and egr stuff is deleted, is that enough to cause all these idle issues?

Definitely not. I deleted all that stuff a long time ago and haven't had any idle problems.
Vacuum leaks seem to be a common cause of idle problems on older vehicles when rubber/plastic hoses tend to crack/break. I know you said almost everything is new but what about the rubber hoses that go into the passenger and driver's side fenderwells? These are often overlooked and if they cause problems, they can drive you nuts 'cause they're hidden away from view.

 

[99FiveOh]

Cruise has been eliminate as well as all the smog solenoids and charcoal canister. So no lines going into either fenderwell. All hoses are brand new and clamped/ziptied on. There no vacuum leaks that I am aware of. I've been under the dash too with the car running and I couldn't hear anything. When I first got the car together and running the little bulb behind the glove box had come loose, but I fixed that right off.

It's puzzling! Could turbulence from a CAI cause this? I may put the factory airbox back in to see what happens.

 

[Bullitt95]

Could turbulence from a CAI cause this?

Possibly. If the air filter is exposed to fan wash, the surges of extra air can upset the MAF outputs and cause idle problems. The MAF also needs a straight flow of air coming into it so if the CAI pipe has a bend before the MAF, that can also throw off the MAF output voltage.

 

[99FiveOh]

Yes, it's a fenderwell CAI. It's just puzzling why the CE light coming on would smooth out the idle.

 

[Zero Signal]

I didn't realize you deleted all the smog equipment. Now I do think it may be tune related. If the EEC thinks your EGR and purge solenoid are working and they're not, it will definitely cause issues and trigger CE light. It's not getting any feedback from the EGR position sensor.

The smog pump is a mostly-passive system and shouldn't affect anything if removed as long as the vacuum line to it is plugged.

I'm thinking your issue is probably vacuum related and/or computer issues as a result of the smog, EGR + purge delete.

You said you're confident in the current sensors, but did you probe them to verify the wiring was still good?

 

[turbogt]

I've never experienced this issue either

 

[99FiveOh]

You also drive a Cobra. I'm not sure that they suffer the same fate. Different engine combo and computer/tuning might be the difference.

 

[turbogt]

You also drive a Cobra. I'm not sure that they suffer the same fate. Different engine combo and computer/tuning might be the difference.

After reading this thread, you'd think I would have figured that out

 

[sixt9coug]

I've "kind of" experienced this BUT....

Car is hot
start car
AC on
Bogs down hard when AC clutch engages
sometimes will stall.

However, it will ONLY happen because of the AC clutch engaging. If I turn the AC off, it's never done it. Also, after driving it for a couple minutes, I can turn the AC back on and not have the problem. It's only right after I just start the car after it's hot.

 

[BlackVert]

right ... i forgot that you are essentially stock right now, sorry. you might try going to a stock intake setup (ie-no fenderwell cai), just to see what happens

 

[99FiveOh]

That will be difficult though with the fox throttle body setup.