Why is my idle higher while coasting than when I'm stopped?

[mwebb]

the VSS is a load signal
the ECM sees it and has been programmed to do certain things when the car is moving faster or slower or stopped

if you tamper with the IAC the ECM will see that
and it will respond as it has been programmed
the ECM can control idle speed with ignition timing AND your faster idle while rolling may be a result of that as opposed to change in IAC command

you may want to connect a scan tool
a real scan tool not a wheel chock code reader or
scangauge
and drive around watching IAC command and IGN timing command
with VSS
with TPS or closed throttle switch

just to learn more about your system , before you start
fixing that which is not broken .

[IsaacCarlson]

Some auto's will idle at a higher rpm when moving to better match revs when going back into gear. If the idle were too low, you would feel a clunk as the tranny re-engaged.

[Maniak]

I know on some of the Fords (I know, not same vehicle), that the ECM is programmed to hold the rpms up when shifting (manual trans) . It will also increase the rpms while coasting in neutral.

For example, we were waiting in a long line of cars trying to get over the Hoover Damn. We were facing down hill, so I just put the car in neutral (wasn't going to turn it off, was way too hot) and just used the brakes to let us go forward. At about 15 mph the ecm had the rpms at almost 2000. If I stepped on the clutch they would come down.

I asked a few people about reprogramming the ecm to get rid of that feature and to get rid of the RPM hang is has when we are shifting, but haven't gotten any farther into it. I just hold the clutch in when I'm doing my coasting in that vehicle.


~Mark