I just helped someone with a ZZ4, LT4 hot cam, and TPI. His IAC worked like stock. He's pulling around the same vacuum as me.

I have a less lumpy cam and a Edeljunk base and runners on a 355 L98. My IAC cannot control the idle. If I apply more load, like the A/C, the IAC goes wide open and barely helps the idle. My IAC passages (at least some) are open because a shot of carb cleaner into the IAC hole stimbles the engine, but I wonder if the Edelcrap IAC passages are not as big as stock - or maybe just partially blocked. With as much work as I put in to make that overpriced junk fit and perform, blocked IAC passages wouldn't surprise me. Any thoughts/experiences?

 

Is the IAC really good?.
Do the full retact and then the unplug while idling and measure the difference to make sure it's moving. The scanner just reports commanded numbers.

try richer at idle, maybe the timing is way off. You have to play alot at times to get the idle right.

 

Grumpy, is there any need to reset the computer by pulling power after resetting timing?

 

Depending on what all you've been doing it will relearn the fueling corrections quicker. While minor, changing timing changes the engine vac..

 

This may not be the "right" thing to do but maybe you need to open the blades a little more to get some additional airflow at idle. This is assuming that the TB is very clean. Many production cars have a hole drilled in the blades for more air at idle but the same throttle angle (for tps), just like we've been doing to carbs all these years. If the IAC counts are excessive, this may bring them down to a reasonable level. If they are where they're supposed to be than I would say that you have another problem, specifically timing like Grumpy said. Even not so lumpy cams like additional timing at idle.

 

The GN has (2) 1/8" holes in the butterfly, that I added. I had to do that to get the min, and max TPS volts right. Yes, for various reasons SOME cams take alot of air at idle.

 

I'm at a livable compromise right now. The TB is open enough to idle beautifully (except when cold). When I turn on the A/C, the IAC goes wide open and does nothing for the idle. On cold startup, the IAC goes wide open and doesn't really help. At full throttle, the IAC goes wide open. She's a little rich in open loop idle and spark is set up for max vacuum. I'll check the IAC to see if it's moving.

 

Sounds like you need to open the blades a little more it the IAC is maxxed out and not helping. Try it and move them back if it hurts.

 

Might be too lean

 

She's on the rich side. It's got to be the IAC itself or the passages.

 

Just a few observations here. What are the IAC counts at idle when its idle is fine? When you turn on the AC and the counts go wide open and it doesn't do anything, disconnect the IAC and turn the AC off. Does the idle go sky high? You say it's rich at idle. What's the BL numbers? What do the plugs look like? How lumpy is your not so lumpy cam: you know, specs. What's your idle TPS setting? Lastly, and I don't want to sound like a jerk, but what's this have to do with prom burning?

[This message has been edited by hectorsn (edited June 18, 2001).]

 

Update - I borrowed a Tech 1 that can control commanded idle. Raising or lowering the commanded idle in real time made NO change on actual idle. I think the IAC is shot. I knew the cam made enough compression to allow the IAC to do its job. Hectorsn - trying to get the idle right with a cammed Chevy FI system has a lot to do with chip burning - I think I've done good with the fuel and spark, but the air (IAC) has been giving me problems.