Hi guys, I finally have a Moates Burn1 and a homemade ALDL cable for my 327 TPI retrofit project. In around 10 burns, I have a chip that runs incredibly well and has impeccable driveability (except for what I will describe below). This amazes me, because I have a very choppy long duration hydraulic cam. MAF is really a great system to work with with a radical fuel injected setup.

The only driveability problem I notice is that as I drive the car, warmed up in closed loop, the idle starts creeping up. It seems like every time I stop at a light, the revs settle just barely higher than the did at the previous stoplight. After maybe 20 minutes of driving, my 750 rpm closed loop idle (which is usually more like 800) ends up at 1000 rpms. It will eventually reach 1100 sometimes, and it starts hunting when it gets this high. When the idle is close to target at around 800, it is very stable and doesn't hunt at all. I have the IAC target speed deadband set at 50 rpms in gear. I am using a 6E mask 1989 Corvette 6 speed manual binary file with a timing table I started from scratch (I patterned it off of the M6 corvette/ M5 3rd gen timing table trends to make the manual trans driveability good, but adapted the advance curves to what I need with big valve iron heads). I've made lots of small changes to the bin w/ Tunerpro. The throttle response is amazing under all load and rpm conditions -- this car is a real monster now, it has so much more midrange punch than it did even when it was running excellent with a Holley 600 doublepumper. The only issue that's annoying me is that the car won't hold its target idle.

Why is my idle creeping up on me? I thought that the IAC may be sticking, but why does it always creep up progressively? If I shut the car off, wait 30 seconds, and restart, I will come back down to the target idle, and then the creeping rising idle syndrome starts all over again. I can't imagine that a sticking IAC would reset itself properly on every key off/on, like mine is. The TPS is reading 0.055 volts at idle through my ALDL connection and also w/ a multimeter. The throttle body is very tight, so the throttle shaft is not binding or anything, which could have caused the car to hang the idle up.

The idle creeping up does not directly correlate to higher engine temperatures. This car warms up very fast, in only a few minutes driving. I can have a great smooth, target idle speed with the car at 180 degrees, 5-10 minutes after I started driving. However, if I continue driving, even at the same 180 degree temp, the idle will progressively rise on me. The car does not exceed 195-200 under any conditions (thanks to a Ford 2 speed fan from a 5.0 T bird)

I hope it's not a big deal to get this wandering upward from the target idle speed fixed. The car drives so excellent with the TPI on it and my diy tuning that I hate to have one little thing nagging at me.

 

Shut car off, start car, and with idle at "proper" RPM, unplug the IAC.

if it still creeps, then you have a vacuum leak somehow somewhere, or for some reason the timing is creeping up. I don't know much of anything about 6E because I use and prefer 8D.

have you hooked up a data logger to see what's going on? it would be helpful to know if the computer is asking the idle to go up (increasing the IAC steps, or adding in timing) or if the idle is going up with NO corresponding change in IAC or timing (vacuum leak).

 

91, I haven't had a change to datalog the car while I"m driving it -- this will be tomorrow's (well, today's at this hour) project. My laptop (PIII 900 Mhz) is such an old POS that the battery doesn't hold a charge anymore. I was going to run my power inverter to power the laptop, but what'dya know, the cigarate lighter in my car doesn't work. I'll have to investigate tomorrow so I can get the inverter plugged in.

HOWEVER -- I won't be able to get any info. on idle IAC counts from datalogging. With the 6E mask, you must leave the 10k resistor in place or the ECU will stop transmitting data. This immediately commands a 1000 rpm high idle for ALDL mode. I'll try your suggestion of unplugging the IAC when the car gets to warm 750-800 rpm idle, and then keep driving to see if the idle still creeps up. I can't imagine that it's a vacuum leak, because shutting the car down once the idle has creeped too high and restarting gets it right back down to the correct idle speed, where it will stay for a while. The IAC is such a pain, but it's a great tool a the same time. I haven't pulled the IAC off ever, so it's possible it's really filthy and I don't know about it. Hmmmm, I did machining inside the plenum with the IAC still installed, and I never removed it to clean it. This can't be good. Might be time for a new IAC.

 

On both of the $6e cars I have logged/tuned I was able to remove the resistor after data transmission started. This is with datamaster as well as Tunerpro RT. Check to make sure the IAC is clean and there are no deposits in the cavity where the IAC operates. As you said the IAC can be a pain, but it's nice to have for idle control when cold.