Irritating Stalling Issue...very frustrated PLEASE HELP!

[91LX_5L]

Well after I thought I got my stang running great it picks up another gremlin...

I dropped my fuel pressure to get rid of my back firing problem, this worked, I also upped my timing to 14*. Then I adjusted my air bypass screw? (one in my 70mm bbk throttle body) to get my hanging idle slightly lower. But ever since I did that its been idling funny, and I put it back to excatlly where it was.

Anyways this is what happens... Now keep in mind I have a H/C/I 94 5.0 so I got the slight hanging idle issue. (better then it ever has been lately though)

Crusing down highway, see red light, shift down, get down to 1st gear then put it clutch/pop into neutral untill I come to a complete stop....Now before I stop my RPMS hang for a full second at 1k rpm then drop down perfectly to approx 700 rpm...BUT as soon as I come to a COMPLETE STOP a second later they hop up about +300rpm then drop down to about 500rpm and the car stalls. Its weird because it doesnt stall untill I come to a complete stop I could be coasting down a hill in neautral and it will sit perfect at 700 rpm but as soon as I stop it surges up slightly then drops down and stalls.

Now why not just turn up my idle via the throttle return screw? Because I did this, I set it to about 800ish rpm but then my idle would hang for about 2 seconds at 1500rpm then drop down to like 1100rpm hang again then finally drop to 800...this is annoying as hell, I would rather rev it at a light to stop it from stalling.

ANY IDEAS?!!?!? My Plugs are a season old (only drive my car summer time weekends really), my wires, cap, rotor are 2 seasons old. Cleaned my MAF and IAC last season. The car doesnt seem to have quite the power it should, unless its just my imagination.


THANK YOU IN ADVANCE!!!!

 

[HISSIN50]

Hey bud. You're right on in your IAC thinking. Mods aside, because you narrowed it down to occuring as soon as you become stationary, that's telling.

Is your bleed screw in most of the way? I'd want it run fairly far in, and use the stop screw for the adjustment. FWIW, on my car, if I had the bleed further than 1.5 turns-out (from being seated), it would hang. I just use the stop screw.

The rolling hanging is totally normal but for some reason the IAC is burping when you stop. You dont have a TwEECer (you did and sold it?). Otherwise you could dial out the rolling idle increase.

How is your idle set? Did you set it with the IAC disconnected (on a hot motor, with no accessories on)? I've had very good luck doing it that way, but with your mods, I'm not sure if it will play nice. The computer and IAC have an easy time adding RPM but cant lower RPM if the IAC dutycyle is 0. Any meaningful amount of no load, hot idle IAC function can lead to surging in some cases.

I'm sure Grady and others will have some good ideas. My random thoughts.


Good luck.

 

[Killercanary]

Maybe I can learn something new here...


I've always had a firm belief that in the 94-95 cars touching the IAC is a BAD idea. I've seen a LOT of post like this and after getting my eec tuner I made my own assumption that since the idle is controlled via the EEC messing with the IAC is not a permanent cure. Is my assumption wrong? If so, why? I know this doesn't answer your questions Matt, but it may help to in discussion. I know there are three idle setting in the eec, one is a neutral idle, one is a "coasting idle" and I forget what the other one is. That's what I get for having a car that has been down for nearly 2 years now. DOH!

 

[HISSIN50]

Paul, I'm sure you're right, but what do you mean about touching the IAC? In what respect?

I'm not all into the tuning stuff, but the third idle setting might be something along the lines of the dashpot........letting off the gas inbetween shifts .

 

[final5-0]

If I say Bacon ... You think Eggs

If I say modded 5.O Stang ... You think Unstable Idle

Like Paul ... I wanna take this opportunity to learn something

I've always thought only the FMS 65mm tb's had the idle bypass
and
all other aftermarket tb's did not

Ya'll set me straight Please

I'll say more later in this thread!

Grady

 

[chefster]

i am thinkin too much vacumn at sensor[low pressure] ,try better filter

 

[91LX_5L]

i am thinkin too much vacumn at sensor[low pressure] ,try better filter

what filter?

Anyways I have been told you should never really adjust the idle with the throttle stop screw.

I have my bleed screw just about 1/2 turn open (is this bad?)

 

[91LX_5L]

Well I reset my comp, took off the negative batt cable and hit the brakes a few times turned on the headlight switch. Then I fired up checked my TPS, it was a bit out so I adjusted my throttle return screw till it was at .97, then reset the comp again and it runs good now...no stalling!!!

 

[WhiteDevil]

If I say Bacon ... You think Eggs

If I say modded 5.O Stang ... You think Unstable Idle

Like Paul ... I wanna take this opportunity to learn something

I've always thought only the FMS 65mm tb's had the idle bypass
and
all other aftermarket tb's did not

Ya'll set me straight Please

I'll say more later in this thread!

Grady

My BBK 75mm has a bleed screw.
I think there are scalars with my tweecer for
Neutral idle
Coasting Idle(has a different name)
Idle in gear

 

[HISSIN50]

Matt, the pure tuners will tell ya to not touch the idle stop screw. They work around the commanded idle and tune away if necessary.

For some of us, that don't work. We'd love to do it the right way if we could, but we cant. So hosing with the throttle stop screw can work. Your idle might degrade after some adapting occurs. Kind of a crap shoot.

Let's hope it stays good!
Good luck.

 

[final5-0]

My BBK 75mm has a bleed screw.
I think there are scalars with my tweecer for
Neutral idle
Coasting Idle(has a different name)
Idle in gear

Yes John

tb airflow scalar, neutral idle airflow functions, and the first few points of the maf curve can be tweeced to help with an unstable idle.

Another thing that can cause the idle to go sour at long stop lights is the O2's can cool too much. That mostly happens with LT's and the funny thing is, it can happen to some, but not others.

Too much spark at idle can cause the idle to be unstable as well.

Thanks for the tb info. For some reason, I had it in my mind only oem tb's had the bleed screw

Grady