Doesn't idle down untill car stops?????

Jason 302

10 Year Member
Aug 9, 2003
685
71
68
Newark, Ohio
Doesn't idle down until car stops?????

I put a self built 306 motor in a couple weekends ago and I've noticed while driving it that it doesn't drop down to normal idle (around 1000rpm) until the car comes to a stop or near stop. While coasting in neutral it will stay up around 1300-1400 and then drops when I come to a stop. I never noticed my stock motor doing this. Is there anyway for the computer to know how fast your car is traveling and it adjusts the IAC somehow? Anybody have an answer? It's not really a problem just a little annoying that I don't know why!
 
The VSS sensor located on the speedo cable is supposed to signal the computer to open the IAC a little to increase idle speed. It does this so that you don't stall as you slow to a stop.

The other possiblities are sticking linkage, dirty IAC , dirty throttle body and TPS sensor going bad.