If I want to lean out my idle mixture, do I need to increase or decreas my IAC counts? I am still a bit rich at idle (although nice and smooth now) and would like to lean it out a bit. TIA

 

IAC counts do not affect the idle AFR. IIRC you are using a TBI setup? And, is this after it idles for a while, or right after startup? The reason I ask is that there is enrichment in affect from startup that decays out over time. Otherwise the AFR is commanded from the open loop AFR table(s).

Are the idle BLMs in line once it goes closed loop?

RBob.

 

RBob,

Thanks for the speedy reply! I've got things leaned out enough in O/L so that I'm no longer blowing clouds of black smoke, but I have two little problems that I would to take care of. The first is that right after start up, as soon as the idle stablizes (about 5 seconds after start up) the idle drops to 700 RPM. The problem with this is that I have commanded a 1000RPM O/L idle (for now until I get things dialed in a bit better) and the exhaust still smells pretty rich. I was thinking that introducing a little more air with the IAC. The second problem that I'm experiencing is the C/L idle. It is set for 750RPMs but it is idling right at 1000RPMs, but at idle the BLMs are rock steady at 128 (and I know that MUCH datalogging while driving is in my future)

I'm pretty sure that the O2 sensor may be FUBARed because of running so rich at start up for so long, and a new set of plugs probably isn't a bad idea either. I'll be putting in a new heated O2 sensor and set of plugs this weekend, so before I go any further, I would like to know more of what I am doing this time.

 

Which ECM are you using?

Some ECM/masks don't control the exact idle speed until the engine is up to a certian temperature. One thing to look at is the IAC counts at idle. If at 0 the idle speed can not be further reduced.

Are you using a 10K resistor across A&B of the ALDL?

RBob.

 

I'm not 100% sure of the ECM that is in my 88 Blazer, but I am using the 7747 mine.ecu imported and saved as an .xdf. I started out with a AJAK bin and modified the VE tables and spark curves to what I was running. I know I am still rich in O/L because of the popping in the exhaust when I drive it in O/L. As far as ALDL goes, I didn't need the resister to obtain the readings.

I still have a bit to go before I reach 0 on the IAC counts. Here's what I am running right now for IAC vs Temp:

Temp C IAC

cold 55
-9 50
6 45
16 42
24 38
31 33
37 30
43 25
49 24
above 24


I think I might add about 5% to the IAC counts below 43 degrees C and see what happens. If I don't notice anything, I might add another 5% or so.

Another thing that I have noticed is that the exhaust note has a burbbling sound since I lowered the IAC counts. It's almost like you can hear each cylinder firing. I know that can't be right because the idle is around 800 RPMs.

Any ideas?

TIA