Dies when rpms come down

[00 Red SS]

My car will idle just fine but if you rev it and let the rpms come down then the car will just die instead of dropping to idle speed. When i slow for a stop or turn and put the clutch or go to netural the car dies. It idles around 720rpms, i just swapped on a different iab and tps and nothing changed . What do i need to check and fix?

 

[HISSIN50]

sounds like your VSS is taking a poo poo on you.

 

[00 Red SS]

How would i check it and how does it affect it whens the cars sitting still and rev'd? Someone told me to unplug the iab reset the idle maybe check the tps and it should be fine.
Now that i think about it theres nothing hooked up to my T5 right now so the VSS shouldnt be getting any reading at all, my speedo cable was the only thing connected and it burned against the header. I didnt have the problem when the speedo worked do you think it is a possibility?

 

[blk92stangg]

The VSS piggy backs onto the speedo cable, and there is a harness plug that goes to the VSS. If that plug was never connected, then the speedo not working should not affect anything. If you do have it plugged in, then I would say that the speedo not working could absolutely be something to look at. I would also not assume that the IAC you swapped on was good, unless it was brand new. If the IAC is not working, the ECU would not be able to maintain idle when loads are place on the engine. I would also look to see if you have coking around the throttlebody butterfly, or if the stop is adjusted closed. In either case, the engine won't get enough air to idle, so the iac has to compensate and open more to maintain idle. If the IAC is faulty, it won't be able to supply enough air flow, and your engine dies. As always, YMMV. Good luck, I know how irritating idle issues are.