I'm having a few problems getting a slow idle after fitting my ITBs and it is probably due to the butterflies not sealing perfectly (3 attempts at this now). I can get it stable at 1100rpm and I just want to bring it down to 800 - 900rpm. Clearly I can't adjust the idle in the normal way so I thought maybe a bit of creative mapping might help.

What is the best way to do this? Do I simply retard the ignition more aggressively at 800rpm and get it back to normal at 900rpm? Any thoughts guys?

Run it down to maybe 2 or 3 deg at idle, should slow it down and wont cause any major problems.

Youll need to fiddle with the values just off idle to sort the throttle response, but just ramp it up to normal values pretty quick. I assume you are running TPS based advance?

I know of people running negative timing at idle with roller throttles to pull the idle speed down enough to make it sensible.

Try loosening the throttle butterfly's and snapping them shut, then retighten them. If the butterfly isnt central it can cause high idle problems.

I have carefully fitted the butterflies 3 times now and this is the best result I could get. I even applied some Molykote 321 which improved things enormously but I still can't get it lower than 1100rpm - I guess 12 burrerflies is just too much

Here is my timing at the moment ...


Description

Flak - you say to run it down to 2-3 degrees at idle. Ermmmm I'm about that now and considerably more at anything lower - any ideas?

p.s. It is indeed a TPS based setup

[Edited on 1-12-10 by RazMan]

Update: I have had some success! I took the timing @ 1000-1750rpm down to 2 degrees and presto! - it idles at 850rpm with an AFR of 13.5 I also tried 1 degree but I could hear some farting in the trumpets so I thought that was a little too far.
That's a relief as my ITB project was looking a bit compromised.

Thanks Flak - you were spot on!

Good stuff.

I wonder where he learned this trick?

http://www.locostbuilders.co.uk/viewthread.php?tid=131856

Yep, I speak from personal experience

Its what I like about these sorts of projects, you always learn loads of stuff, which hopefully then helps someone else out...

quote:

---

Originally posted by flak monkey
Its what I like about these sorts of projects, you always learn loads of stuff, which hopefully then helps someone else out...

---

quote:

---

Originally posted by flak monkey
Yep, I speak from personal experience

Its what I like about these sorts of projects, you always learn loads of stuff, which hopefully then helps someone else out...

---

what is your TPS voltage at close?

this effects MBE idle a lot, can cause massive flat sopts with throttle pick up if not correct. so for MBE is VITALLY important.

generally MBE systems idle and anti stall very well if the base set up is correct. 5degrees ignition at idle works very well with MBE on most engines.

- colin.

Hi Colin, I had to re-index the TPS for the ITBs and it is now ~0.43v (closed) and ~3.48v (WOT) - is this ok? Also I found that increasing the fuel gain was necessary to get some more headroom in the map, although I haven't started any road tests yet.
I was exploring the MBE sample maps and all of them seem to use 0deg advance at idle and I found that 1-2deg was about right for me, although I will need a session on your dyno eventually to get things set up properly

as long as your TPS reading moves as soon as you open the throttle then its ok.

what normally happens when its set incorrect is you will open the throttle the first few % and the ecu will not register any voltage change, so doesnt add in any extra fuel for opening of the throttle.. so you get a horrible flat spot that no ammount of mapping can get rid of. so makes pulling away, or very light throttle driving very horrid.

- colin.

Ah ok I see what you mean now. I already made that schoolboy error when I first tried to start the engine and wondered why I wasn't getting any fuel to the injectors. At least I'm learning by my own mistakes though

your own mistakes are the easiest to learn from.

good stuff

if your ever in any doubt, feel free to send me over your map file and i can take a look over it for you: info@atspeedracing.co.uk

- colin.

That's very kind mate - U2U sent