SSkeet

This is on a big cube, big cam, big heads, big 90/90 intake setup ls1

I tried the method of getting the IAC down by using the set screw and resetting the system by pulling the plugs, turning on the car, and then turning it off and plugging back in, but when I got to the point where the car actually ran and idled decently, the tps was .85 and the IAC counts at idle will drop to ZERO while the car still runs.

I know this is too much tps voltage, so I did the set screw back down to .58 and the car will only fire and then quit...I am guessing its not getting enough air?

My question is...
What do I do at this point? Drill the TB with the TPS at .58 until the car actually runs?????????????????????

From what I have read, the TPS voltage cannot be any more than .6

Ragtop 99

iTrader: (7)

With big cubes, I do not see a problem with drilling a small hole in the TB. I'd start very small and target .4%

SSkeet

.4 voltage or .4% tps?

I dont think there is a way for me to use the set screw since I know I am not supposed to exceed .6 volts tps. I think this is something people overlook. If you exceed .6 the pcm will reference the wrong cells or something...

But if anyone objects, let me know. I will not drill...

SSkeet

Well I tried to get the idle right by adjusting the set screw again (after some drilling) and I got it to .8 tps voltage and it idles nice but the idle IAC goes to 0 and if I drive it, I get the cruise effect big time.

So I set the screw back down to .58 and did some VE and Park position tuning and got it to run decently but at low rpm if I come to a sudden stop the idle rpm dips way down to like 400 and then recovers (sort of surging).

Should I drill more? I am guessing that maybe when I let off the gas, there is not enough air flow when the TB closes and that is what causes the surge???

Any1??

P Mack

iTrader: (6)

I would recommend setting the idle screw to where it idles with IAC counts about 20, and make sure you're still in the idle fuel trim cell. If you've moved out of the idle fuel trim cell, back off until you're back in it. Then move your Desired IAC steps vs Desired Effective Area table to the right one cell for every 10 steps your IAC counts changed when you adjusted the screw (this is a new method i haven't actually tried yet). Then if you still have the cruise control effect reduce your throttle cracker or throttle follower tables until it goes away. If the idle hangs forever until you come to a stop adjust your throttle cracker. If it hangs for a couple seconds at whatever speed adjust your throttle follower.

SSkeet

I ended up drilling it to 1/4" and the IAC's are nice right around 40 at neutral idle and idle feels nice. Part throttle is fine, I can now come to a complete stop and it doesnt bog or surge or anything.

The only problem I have now is that if I get on it a little bit as I am starting out and then all of a sudden let off the gas and push the clutch in and hit the brake, it will drop down to like 400rpm like its about to die and then recover (only sometimes it does this).
How can I prevent it from dropping like this? Seems like I should almost do the opposite with the throttle cracker or follower. Can I adjust the follower to keep the rpms up for just slightly longer when I let off the gas to correct this???? Or is that just a bandaid fix?

If I need to try anything else I will consider what you suggested...

P Mack

iTrader: (6)

Try increasing your idle airflow by 1 g/s or so and see if that helps. Otherwise your car might like IACs at 30 instead.

Throttle cracker doesn't work below 1mph anyway, and putting a value in for throttle follower at 0% throttle doesn't make any sense.

SSkeet

I ended up raising the idle airflow a bit and it seemed to help but would still surge a little down to like 600 instead of 3-400. Raised it more and same thing...
So I actually put 1 second in the throttle follower delay table between 0 and 20mph (I should change it to 0-5 or 0-10mph) and it works nice. Whenever I get on it at low speed and let off real suddenly, the car stays at around 1100 for about a second then immediately finds its home at 950. Running nice now and IAC about 40 at dead idle.