when i was home last i got a little crazy and threw a carb on my car
edelbrock 1405
very easy to tune
it still has the carb on there... for a few reasons
one of the most major reasons might have to do with the IAC

with the tbi, when im letting the clutch out making tight turns or just trying to cruise along slowly, the car starts to buck like bronco. Feels like the iac is opening and closing liek crazy. Makes the car a real real pain to drive. With the carb I realized that was not the way the car should drive as its smooth as glass in the same situations, same timing curve and all.. so it has to be iac or fuel related (didnt have the chance to drive it sans IAC just for the hell of it but i suppose that would narrow it down)
So would this have to do with the throttle follower crazyness im hearing about. BTW j prevost i too find that rpm hang extremely annoying, atleast you arent shifting your own gears, when i shift mine it almost feels like i have a vacuum leak and the subsequent lurch especially when cold sucks

 

You might try changing the filter coefficient to something that provides less hang time.
J

 

So this throttle hang thing maybe what i have been experiencing?? I thought that there was something wrong with the tps, or possibly the throttle sticking. I know absolutely nothing about prom burning, unfortunately haven't gotten any of the stuff yet. And don't understand 95% of what you guys talk about on this board. But i know when it is cold my car does a similar thing with the idle staying up and then coming down slowly. When it warms up it does it but it isn't as noticeable. And if i don't tap the gas when it is cold it will stay up there for while until the car has warmed up. Jprevost you are right it is pretty annoying. I'll have to keep this in mind.

 

gm throttle bodys are fairly well known for throttle shaft bushing wear. air cleaner off engine off grab throttle lever twist to open butterflies halfway. wiggle about. got play? 2 things-vacuum leak and in advanced stages-butterflies hang open with resulting "idle" speed of around 1100. if not too worn a good carb. shop can re-bush for that like new throttle body feel.

 

I've got a holley 670cfm TB unit that's been doing this since it was brand new. The spring on the holley unit is beef and it closes the TB no problem (let off throttle, car slows down real fast until it gets to around 1500rpm where I suspect the IAC is having it's fun).
Pablo, you think it's bad with a stick...at least you can take it out of gear! I'm stuck with a stock torque converter and this problem. I've got an exhaut leak right now that's taking priority but once I fix that I'm going to do some major work with the IAC. First thing I'm going to do is drive around with the IAC unplugged and closed! I'll set the min idle to around 1000rpm and I'll see what the gets me.
I have a feeling that the IAC is just not tuned for a larger motor. On every slight downgrade I find myself driving with the brake and the IAC is always between 40 and 80 counts.
I think I might run into VE table problems if I disable the IAC completely since the IAC is a vac leak it'll need even MORE tuning, ~sigh~

 

try this test if you are feeling experimental- disconnect whatever device that controls the speedometer-cable or sender-take it for a drive and see how the thing behaves. prolly will ck.engine light yourself until its reconnected. but it will allow you to start aiming in your quest to conquer this. also the bigger the spring the worse wear will be on a shaft bushing. i guess what i am trying to convey is that the return spring is only one part of what is going on there. if the shaft/bushings are worn then vacuum leaks will happen around the shaft cuz the diameter of the bushing is way big. spray bushings and shaft area with carb cleaner to verify no leaks. upon decel prior to hitting the brakes iac counts are what? how about after you apply them. tcc should disengage when the brake pedal is lightly applied. is any incorrect signal being sent to the ecm, like ac is on, maybe the power steering pressure switch-but i dont think one that applies here. p-n switch is indicating proper gear selection? any other inputs you have that would normally cause the ecm to add counts. there are also a couplefew different pintle designs on the iac. been down that road and the incorrect one will fit in and make the idle speed so screwy you chase your tail till it is figured out. just a couple thoughts that may help out. later