need help with idle with FAST

[fast4d]

It would be awesome if you guys would suggest what I should try next.



I switched from S/C to turbo and also installed a mild turbo friendly cam from cam motion. I get 18" of vaccum @ 1100rpm

Now I'm trying to set idle. I can get it to idle steady and smooth at 1150-1200 rpm. This is with the idle speed set at 1000 in the idle table.

For some reason I can't get it to idle lower with the idle speed surging up and down. I would like 900rpm. this is a manual trans.


The idle follower is about 60-70.

timing advance is 28 deg. I've tried 20-33 deg.

I'm using open loop until 2000 rpm.

a/f target for idle is 14.4 (I've tried 13.8 - 14.7)

VE at the cells during idle is 89-93

 

[bobc455]

89-93 seems quite high for VE values at idle.

What is the IAC position?

Can you close your throttle blades any further (with the idle setscrew on the throttle body)?

-Bob Cunningham

 

[fast4d]

Originally posted by bobc455
89-93 seems quite high for VE values at idle.

What is the IAC position?

Can you close your throttle blades any further (with the idle setscrew on the throttle body)?

-Bob Cunningham

IAC is about 50-60 (moves around during idle)

I can close the TB a little more but the idle will start hunting and I can't seem to rid of the surging playing with the VE nor timing.

 

[bobc455]

Okay- I misunderstood your problem the first time. I thought the idle was too high and you couldn't get it down. Your real problem is surging.

When I set the idle, I like to have the idle controled with the idle setscrew, and have very little movement of the IAC motor. I will adjust the setscrew so that the IAC position goes to 10- that way virtually all the air is going through the throttle blades instead of through the IAC passage. That would be my advice- open the throttle blade(s) far enough so the IAC isn't moving above 10 (unless the engine is cold).

In theory you could adjust the IAC P and D values, but this is kinda a pain, and I've never seen a good written procedure on how to set these. I'd love to see one if someone can describe how to do these!

Other common causes of surging at idle are running too lean or too much timing.

If you have VE values of 90-ish at idle, what is your actual A/F as indicated by the O2 sensor? That seems weird. Do you have the right injector size in your setup? My VE at WOT is around 85, seems weird that you need more at idle.

I'm still not sure why the motor idles at 1150 if your setpoint is 1000. Is the 1150 indicated by Calcom or by a tach?

-Bob Cunningham

 

[Craig Smith]

I think you need to richen the idle a bit. Set the target at 13.0:1 and try that. Do you REALLY have to have VE numbers that high to get the target and actual a/f to match? What is your injector opening time set to in the global setup parameters screen? I am going to guess you have it set very low, like less than 0.5 mS. Is this a good guess?

I would give it more throttle blade as well. Keep the IAC down around 20 or so at idle. Sometimes I think trying to feed an engine entirely from a 1/4" diameter hole causes air distribution problems that screw up your idle. Relying more on the throttle blade for air than the IAC motor would help this.

 

[Craig Smith]

One other thing... if for some reason all else fails and it continues to surge, try throwing timing trim at it. That typically helps a lot when other methods don't work as well as hoped.

 

[fast4d]

thanks bob and craig. I'll close the TB some more and go from there.

1 thing that's odd to me is that when I got the idle nice and steady at 1200rpm, I changed the idle timing trim from all zeros to 1 - 5 deg (from left to right) and it started surging again. So I zeroed it again.


but I understand that the timing trim should only be used as a last resort to smooth idle speed.

 

[Ricky Trussell]

thanks bob and craig. I'll close the TB some more and go from there.

I think they are saying open your TB blades so your IAC closes letting the TB control air into the engine. The IAC could be making wide swings and the engine hunts around.

What is your injector opening time set to in the global setup parameters screen? I am going to guess you have it set very low, like less than 0.5 mS. Is this a good guess?

Craig, or anyone else as for as that goes.... What reason would you set your injector opening time other than 1.0mS ?? Say I have 42 lb. injectors and a 1.0mS setting and I change my opening time to .5mS. Would I not be just leaning the engine out and have to change my VE table to get back to my A/F target???

Not trying to steal the thread, but see a good chance to learn here. Thanks

 

[fast4d]

OK. I misunderstood. I need to OPEN the TB more so that the IAC valve won't be relied upon so much.


As far as injector response time I left it at default at 1ms.

Even when I had the blower my VE went up over 100 as it moved to the upper right side of the table.

 

[S351 R]

FWIW, my vortech/351 refuses to idle below 1050 without the typical surging. Tried everything except adding timing above 32. Also, inj opening is set at 1.3 ms which behaved much more nicely with my 72's in traffic/idle. Adding .ms there will really only richen up idle/ light throttle conditions so it may be worth playing with


Kirk