ben73

I have a problem where the 2.20" TB's on my Crossfire Corvette make the throttle too touchy just off idle.

It cruises at 65mph with TPS at about 3% and this makes it a little unpleasant to drive.
I have a set of 2" TB's that I haven't used in over 10 years, but my notes said that these were a restriction at WOT, showing about 93 or 94kPa MAP. The 2.20's show 100kPa MAP at WOT, so I'd like to keep them.

I haven't done any tuning for years, so I'm a bit rusty, but I'm wondering if eliminating any IAC follower action until TPS > 20% (or thereabouts) may help somewhat.
I'm not sure where the IAC sits currently while TPS is at 3-4%, but I'm guessing it is open to some degree, admitting air and therefore requiring less TPS to maintain highway speed.

Has anyone else played with IAC follower tuning to deal with a similar issue?

Thanks!

Dewey316

You need to do a couple of things. #1, know where the IAC is at idle and make sure that it is correct, then adjust the base throttle blade opening.

Second, zeroing out the IAC Follower can negatively effect things like throttle closing. It is there to open the IAC so that when you slam the throttle blades shut, air is still passing through and the engine doesn't stall out, and also to keep it from suddenly flooding the engine with fuel in the time between the throttle closing and sensors and injectors reacting. That is why there is also a IAC Follower decay rate.

Really, if everything is set right, I don't think the throttle follower will open the IAC much when going for 3%-4% and rolling on at the freeway to 15%-20%. It has been a lot of years since i dug into this stuff (mind my memory on this), but it is all based on attack rate of throttle opening.

There are also other parts that interact and at certain MPH reset to the IAC, etc.

How close is your tune at cruise? I found a lot of surging and touchy throttle until I really dialed in my cruise and roll-on / roll-off tuning. It also seemed that pump-shot and some TPS delta based timing helped tone it down.