Got my new 350 in the car, and its running great but one small thing is driving me nuts.

The old 305 did the same thing, so its nothing that happened after swap.

The car will idle up and down when at idle, and will maintain (almost like cruise) speed when letting off of gas, and eventually it will let off throttle and coast. Not a big issue, but its bugging me.

IAC is new and idle speed has been set, TPS is working good and smooth and is set.

What other sensor could be doing this? It still does it even when the IAC is unplugged.

 

did you check for vaccum leaks>?

 

Im sorry that I can't be much help on this matter but this was happening with my firebird with a carbed 355 and 700r4. I think it may have had to do with the tv cable. No problem now... the car is in pieces on the garage floor. -Bob

 

I second the Vacuum leak, another thing to look at is to see if your throttle body is a little sticky. I noticed mine is and would give me a similar issue to the one that you've described. It would work fine, but the idle would remain high when letting off the gas, but if I manually shut the throttle, it would return to normal idle. Keep in mind that the throttle won't stick much at all, I'm talking just a tiny bit of movement where it would "stick", but it was enough to throw the idle off, and let it sit high. Good luck with getting it fixed.