F.A.S.T. question regarding afterstart idle...

[loudbird]

Hey guys, i'm new to the world of fast, and am having trouble with getting a friends car to idle well after a start.

The idle will tend to zoom up and down, and if you dont give it some gas, it will die. After giving it some steady throttle, it will smooth out, and you can pull ur foot off the gas no problem... after its smoothed out you can punch it out of gear, and it will return to idle fine.

a.f/VE tables have been worked out and are in good shape, i just need a few suggestions on what to do about the afterstart idle issue as this is the only time the problem rears its head.

So who has some suggestions on where to start? the IAC vs coolant temp chart places the iac very high compared to the desired line....

Another issue may be the IAC needs to be setup correctly? if so, does someone have a procedure for this?

the car is a 88 firebird formula, with an l98 shortblock, decent cam, auto, superrm setup...

thanks for the pointers ahead of time!


Steve

 

[fast4d]

this is happening when the engine is still "cold"?

sounds like you need some enrichment - base on coolant temp

 

[loudbird]

yes it is worst when the coolant is cooler, but it will do it. not as severely even on a hot start. the motor fires right up in either situation...

i tried with no avail to playing with some of the setting in these table only to return them to where they were before...

seems to me its an adjustment on the IAC, but i have yet to find an adjust procedure...

 

[Ricky Trussell]

Maybe I can help with the IAC.

1) check idle speed vs coolant temp, 950rpm at 75 degrees taper to 800 at 140 degrees.

2) check throttle follower setting. set it at 10 at your idle tps setting.

3) crank the engine and let it warm up.

4) if it will idle, look at your throttle follower to see if it is running at 10 or close to it at your idle speed, if it is above the setting then open your throttlebody blades until it drops to it.

You need to also check your A/F ratio when it is cold to make sure you have enough fuel for the car to run.

If you want you can sent me a .gct and I can look at it.

 

[loudbird]

Thanks ricky - i'll check it out tommorow- the car will idle, it seems that it hunts for a min then finally settles out where it needs to be- we have the WB 02 setup, a/f were adjusted on the base map for idle around 14.5 or so... start up enrichment is around 12-12.5 i think (dont have the laptop at the house here)

You can here it movin the IAC open and closed... the air intake gets very loud when it opens it!

i'll check all that out then report back. Thanks! (i hate being a noob to this stuff lol... i'm learnin tho)

 

[Ricky Trussell]

I talked to Craig about the 14.5 idle A/F and he told me that allot of engines will not idle that lean. Mine will not. I have mine at 13.6. But if it settles down after a while maybe the iac is too active.

 

[loudbird]

Well, that 14.5 # is kind of a guess as to what it is... This afternoon i'll have a chance to sit down infront of the software and see what the real story is.

It really does seem that the IAC is wayyy over active, just by the amount i hear it open and close (through the intake, when it opens the intake gets loud as heck...)

 

[ablackFormula]

I was having the same problem... opening up the throttle blades (by adjusting the manual screw) let enough air past the butterfly to let the engine idle with the IAC counts low. This way, the computer can't stall the engine (which it used to when the IAC counts went too low.) It really helped solve the hunting problem. This was on a 95 LT1 in a Firebird.

 

[mosk]

FWIW, I also had this problem, and was finally able to solve it last week. In my case, I had the WBO2 sensor mounted too far back, and it wasn't getting hot enough at idle to function properly. Relocating the sensor further up the downpipe (~10" from the turbine outlet vs. 30"+) fixed this.

-Jeff

 

[loudbird]

finally got the car tuned prof. this weekend.... we were on the right track - adjusted min thottle for lower aic counts, played with the coolant vs iac chart, and played with the fuel tables...

idles fairly well now, and runs good and strong now too