through tons of trial and error I've been able to get my engine to idle pretty decent with the new cam.

I'm having this problem and I can't figure out what I did to cause it.

the engine won't start unless I give it a bunch of throttle, the IAC is totally shut

if I let off quick it will stall, but if I hold it revved for a second then slowly let it down I can drive the car with no problems at all.

It seems to be just that the IAC is closed during and right after startup.

my IAC park position is 145 which I believe to be all the way open

what am I doing wrong?

 

You may be putting the ECM into clear flood mode. Which means that it is too rich. There is a flag for it in the ALDL stream.

With the '7747, the IAC stays at the park position until the engine is running.

RBob.

 

I'll try hooking up the computer to it and see what it says

it seems like it is parked in the closed position though

not super sure why it would be flooded since I didn't mess with mixture at all

the only thing I did was bump up the idle 50 rpm and add 2 degrees to PE timing

my previous tune was starting fine.

I'll check it with winaldl and see if it's saying anythings funky

 

Maybe the IAC is bad.

RBob.

 

Had a similar problem this week, ended up drilling a small 1/8" hole in the throttle plate to give it just enough air.

My startup IAC position is 80 now and it settles down to around 30 ish, before the hole i had to set the startup IAC to 140 and at warm idle it sat around 90.

What is your idle TPS reading? If it's a fair amount below the idle mode cutoff you can run the idle screw in a little and get some more air.

 

the strange thing is, it was running great before this last chip. I was just tweaking some timing stuff.

I am feeling that something got corrupted somehow. I'm using 2 different xdf files because they each have stuff that is missing from the other. could this screw up my bin file?

I just took the IAC apart and cleaned and greased it. it was giving me trouble a week or so ago but I had it running PERFECT just before this last chip.

my TPS is at .5v just sitting there.

I don't see where winaldl says how many steps the IAC is at. is tunerpro a better aldl program?

when it's cold it starts without pushing the gas but it's rough

if you give it just a bit of gas to get it started and then let off slowly so the IAC logic can kick in, it will run PERFECT the whole rest of the time that it is running.

all I can figure is that something got messed up in one of the IAC tables when I switched xdf files

 

it's just an almost stock 305. shouldn't need a boatload of air, besides, once it's running it works fine. I think this is a problem in my bin file. I just don't know how or why

when I'm about to start it, the IAC pintle is ALL THE WAY SHUT. shouldn't it be at the park position (all the way open)?

 

In Tuner Pro open the current BIN. Then as a compare BIN open one from a few tunes ago. Now do a compare on them: Tools->Difference

RBob.

 

I'll give that a shot. I'll let ya know what I find

Thanks

 

Sounds like it just needs an idle re-learn but i'd compare bins just in case. Start position is usually close to the middle but if the ECM doesn't know where the IAC is at position wise it can put it all the way closed and not know.


There is no feedback from the IAC motor, the computer does it's idle learn after having the battery disconnected for a bit. It basically runs the IAC motor for enough time to close the IAC all the way, that's why it should stall on the first start. On the 2nd start it runs the IAC motor enough time to get it to it's max steps (140-160 depending on the bin file), then it'll back down and settle into the 30's like it should be (assuming stock engine).



for the 2 .xdf's you can just add the missing info to one of them, it's easy. Just make sure to get all the info copied over.

 

With the '7747 ECM ($42), key-off with a running engine does an IAC reset. The ECM steps the IAC fully closed then opens it to the park position. It does this by setting the IAC position within the ECM to 200 steps. Then steps it out to 0 steps, followed by a retract to the park position.

Bam, IAC is now in sync with the ECM. That is as long as the IAC is good.

Option flag dependent the ECM will also do this on an engine stall.

RBob.

 

Aah, sweet. I'm used to the newer codes on the '7730 ($A1). Good info, thanks

 

ok the only difference I see here is that I changed the "IAC motor position vs coolant temp" values in the normal operating temp range from 19 to 29 steps.

I have a weird idea here, do you think that by letting a bunch of air through the IAC, that no air is left to suck the fuel past the throttle plates?

I guess I'll revert my table back to stock and give it a try. not sure why I messed with that.

problem is that all my EPROM burning stuff is at my shop 8 miles from my house and I never seem to be at the right place because all my tools are at home. bothersome.

well hopefully my idea is right!

I'll try it tomorrow, well later today now that it's so late

 

With a warm engine and no additional loads I shoot for 5 - 10 steps at idle (TBI only).

RBob.

 

so you think that the idle stop not being open enough, combined with the IAC open too much would cause the engine to not get the fuel because there's no vacuum left to pull the fuel around the throttle plates?

does this sound like it's my problem?

 

heck yeah!

I punched out my idle setting plug and opened it 1/2 a turn so I can see a tiny crack along the edge of the throttle plates

it starts almost perfect and it idles much much smoother. I'm going to put that IAC vs coolant temp table back to stock and I bet it will be even better

awesome thanks for leading me in the right direction