Stalling Problems

[97yelstang]

Today i was driving my car (97 gt, 5 spd) and coming to a stop... when my car suddenly shut off. So i started it up and drove around for about 5mins then the speedo stopped working then it shot up to 60mph(which is what a was doing) then when i came to a stop sign it shut off again... so i started it and drove off then the speedo didn't work at all... and there is no check engine light and my car keeps stalling at stops but it idles just fine after i start it up.
BTW i have a hypertech chip and dallas speed cal, could they be the problem? also when i let off the gas and let the engine slow me down, it backfires and shoots flames....the car runs great when i'm driving it
and the chip and speed cal were in the car since i bought it with 62k on it and it now has 90k on it
any help would be greatly appreciated

 

[CENTENNIALSTANG]

 

[1tirefire]

I've heard the speedcal makes alot of problems when it goes bad, what exactly, I'm not sure. I'd start with the easier one and take out the chip and if that doesn't fix it, pull the speedcal which is a little more work.

 

[97yelstang]

what about my vss??? cause i was thinking that could be why my speedo and odom are not working which would also tell my iac not to open when coming to a stop because it would think the car is still moving.? and also when i let off the gas it could also tell the iac not to open and that could be the cause of my backfire......does that sound about right?? any other info is greatly appreciated

 

[1tirefire]

Well the vss signal goes to the speedcal and then the signal goes to the gauge cluster and that might be the problem. I don't think the back fire is caused by the iac. Usually when the iac is bad it causes the car to stall and you would have to keep your foot on the pedal to keep the engine running. When you first start the car, does it not want to turn over and stall/not hold an idle?
How about when you come to a stop?Does the car stall? If if does those things its a bad IAC.

 

[gtstangau]

My car likes to stall out alot too.

 

[97yelstang]

well now today my check engine light came on, so i hooked up the ngs and it said code P0500 vss fault
vss 0mph at 2937rpms 100% load. so i road tested the car with the ngs and the mph was at 0 the whole time. so i replaced the vss (because it was cheap) and the problem still exists.
btw 1tirefire my car idles just fine and if i'm driving slow then stop it won't stall its only when i drive at like 40+ mph then come to a stop it will stall, but if i tap the gas when it gets to about 500 rpms(ready to stall) then it will stay running and i was in a traffic jam today and it didn't stall during that but after a 40+mph ride, when i came to a red light it stalled

 

[1tirefire]

Have you actually cleaned the IAC yet? Take it off and spray some throttle body cleaner in it or buy a new one. I bought one 3 months ago for $35. That might cure the problem. But I think the first thing you should do is pull the chip and see if the stalling problem goes away. then I'd clean the IAC if that doesn't work. As for the speedo not working, check all the wires on the speedcal.
That means pulling the outter and inner shift boots and getting the speedcal out and doing a thourogh(so) inspection of the wires. I've heard if the speedcal itself goes bad it can cause alot of problems.

 

[97yelstang]

Finally!!! i found the problem. After hours of tracing the wires (because the person who put the speedcal on had different colored wires) I found that the problem is from the speedcal to the pcm a wire was corroded on the inside...i jumped past it, directly to the pcm and it worked.... so then i replaced that wire...and its all good now.
The speedo and odom work and the stalling is gone and no more backfiring!
just thought i let you guys know

 

[Black Stang 97]

good you found ur problem...my car stalled once on the freeway going downhill on a turn.....it wasnt very fun...the car started right up without a problem....who knows what had caused that...