FAST tps/ idle question

[turbosam6]

I'm trying to tune my new FAST ecm, and I was having a problem with the car dying when you let off the gas driving down the road. I checked the throttle follower, and it was way high on the graph, when it should have been lower. So I adjusted the throttle blade open with the throttle stop screw, and the throttle follower graph looked good, and the car runs much better and doesn't die, but it raised my idle a couple hundred, which I figure it should since I moved the blade. The tps went from 5% to 11% at idle, so I adjusted the tps back down but the idle is still high, and when I start the car the rpms shoot up to 2000 for a few seconds. I'd like them back down to 1400 at start up, how do I get this idle down? It idles at about 1050 now, it was at 900-950 before. I thought adjusting the tps would bring it down, but no luck. And I can't get my tps to read 100%, only gets up to 85%. Is it necessary for it to read 100% at WOT? Thanks for any help!

 

[55Belair]

IT SOUNDS LIKE YOU HAVE THE BUTTERFLIES CLOSED TOO FAR. THE IAC CANNOT CONTROL THE AIR ENOUGH. YOU MAY WANT TO CRACK THEM JUST A LITTLE.

 

[turbosam6]

I know, thats the problem. They are open, and that fixed the one problem, but now I can't get the idle down. Shouldn't the tps bring it back down? And it revs too high on start up, like 2000, then goes down over the course of a minute or so.

 

[bobc455]

When you open the throttle blades further, the engine is going to idle higher. Adjusting the TPS without moving the throttle blades won't bring the idle down- the air is still going into the motor.

It will also allow more air into the motor during cranking, which means you should adjust the "IAC during cranking" setting (since you have more air going through the throttle blades, you can have less air go through the IAC. (I'm guessing that you will also have to reduce the injector PW during cranking)

I like to adjust the throttle blades so that the IAC just barely begins to open during normal idle (it is mostly used during startup & warmup).

The actualy reading of the TPS is not important- if you can adjust it so that the TPS reads between 5% and 20% at idle, and between 80% and 100% at WOT, then you'll be fine. There will be a few minor adjustments like the AE vs. TPS that you'll have to sort out, but leave that to the fine-tuning stages later on.

-Bob Cunningham
bobc@gnttype.org

 

[turbosam6]

How do I get the idle down then? And keep it from shooting to 2000 rpm when I start it?

 

[bobc455]

I'm guessing that you have the throttle blade(s) held so far open at idle that the IAC has no effect. Try closing the throttle blades a little bit, and see if the IAC starts to move above 10.

That should also help keep the engine from revving so fast after it's started.

If it doesn't cure the 2000 RPM revving, then try lowering the "IAC position during cranking" setting.

-Bob Cunningham
bobc@gnttype.org

 

[turbosam6]

Bob, thanks so much. I've got it running pretty good now. I closed the blades a little, and the iac indicator came up and the idle came down. But I have one question. When I burp the throttle in park, it wanted to stumble from being rich, so I leaned out the cells that were rich and fixed it. But then when I actually drive it, those cells come up lean. What do I need to manipulate to fix this? And also when I start it cold, it dies a couple times before it runs. Ideas? Other than occasionally dying when I put in gear, it seems better. Thanks again.

 

[bobc455]

I would put those cells back where they were- I suspect your problem is that you don't have enough "AE vs. TPS". Try increasing that graph to see if it helps- on mine, I almost doubled the graph that came "built in".

Since your car has a turbo (I assume because of your name), you're going to have to adjust both the AE vs. TPS and the AE vs. MAP- hopefully someone else that has done more turbo cars can give you some insight how to tune those.

-Bob Cunningham
bobc@gnttype.org