Today I did the IAC mod at work. Bought 12"x18" 1/16" thick gasket material from car quest(RIP OFF) and went to work. Did the first one with the hole at 3/16" and was having idling issues, kept wollering the hole bigger and it was huge by the time I was done. I got greedy and decided to make another one, without the wollering out of the hole and left it at 3/16". PERFECT. No idling issues or anything. Then I remebered it takes time for your comp to adjust, so some idling issues may be ok. Got uber greedy and then I went even smaller. Made another with a 5/32" hole and no wollering. Car idles, at 650-700ish, waaay too low. BUT when I rev, it falls fast and drooooops to like 450-500ish RPMs, then jumps back up to 650-700ish. I turn my AC and the idle is all over the place, anyway moral is the 3/16" wollered a little is perfect for me. I will be putting the first one back in, first thing in the morning(have thrown the MIL twice within 30 miles under these conds, bummer).

ANYWAY, back to the topic. Normally when I am at idle the TPS reads at 18%, and the GPH(gallons per hour)is at .8, now with the IAC mod, the TPS is still 18%(did you expect anything different??!?!?) BUT now the GPH is at .4. This is all being read from my more than reliable "Scangauge II." So this tank I will put it to the test, most of my driving is done at idle because of horrible Houston traffic, so if the gauge is correct, I should burn half gas at traffic idle than I normally do. I normally get 160-170ish miles to the tank, so well see if there is an increase, and that quoted MPG is at just about any driving cond I do, so if there is any change, it will be from the IAC mod, sorry to make you read a long post....just thought I would share my "DUH!!" moment...

 

Hmmm...interesting...(rubbing my unshaven chin)...

I would be interested to see if you really burn half the gas at idle...

Me and Cliff (CliffyK) had a little discussion on how the IAC mod affects MPG's and we came up with this...the computer (if correctly reading everything) should keep the same A/F ratio with the limited amount of air passage at idle. And thats ONLY at idle, so while the car is dropping revs, for those few miliseconds, the car runs PIG RICH. I doubt that has anything to do with the gas mileage, because it's such a small window of time to run so rich.

I wonder how the diablopicks up the GPH...on what measures it makes the predictions on. If it's reading the amount of air being sucked in, and basing the GPH off that, I would think that because there is maybe half the air supply going into the engine, the GPH would read half as well.

Again, I don't have a tuner, so I have no idea where they get these readings from, and I'm all out on a limb here...it's late, I'm tired...but it was worth a try I guess. Maybe there is SOME truth to what I'm saying...[&:]

 

I have no idea what it calculates. I would have to ask the engineers, lol. BUT it more than likely reads the MAF, I doubt fuel pressure and injectors, probably just the MAF, but for any traffic going stang, this MIGHT be something worth while...?

 

Well if you are correct and it's reading the MAF...then it's basically just being fooled. It's correct in the respect thatthere is half of of the air coming in, so it assumes that there is half the fuel coming in as well. ButI don't think thats the case here...there is half the air, but the same amount of fuel being put in.

Thats my speculation...but it could be completely wrong, so don't quote me on that. Ask Cliff, he's been an automotive engineer for something like 30 years or so. He's wayyyy pro.

 

i wish i could jack with my car while at work...my platoon sgt would probably make me do f'in pushups if he seen my hood up on my car while i was supposed to be "working" lol [8D]

 

I did this mod last weekend. After I put it in, it seemed great, rpms dropping fast, no issues like Ive seen. Drove about 100 miles still no problems.
BUT monday, me and the wife go do our shopping, get out of store go to start the car all I get is this loud clicking. Not the battery just got a redtop optima. It wont turn over, for ****s and giggles I get a jump, same thing.
Reset ecu nothing, check all connections to battery nothing, look for vacuum leaks nothing.
Then Im like hell I got the stock gasket still in the car Ill just throw it back on. And what do ya know, starts right up.
What would have caused this? And I got horrible mileage on my 100 mile trip. I went through almost a half a tank in 100 miles of highway. Now its back to normal. Weird.

 

The PCM knows the vehicle speed (MpH) and fuel consumption in lbs./hour (PpH) --a gallon of gas is between 6.22 and 6.36 or so pounds (PpG) premium weighs more because of the higher density additives).[/align][/align]So, MpG = MpH / (PpH / 6.3).[/align][/align]Keep in mind that when stopped you are really getting 0.0 mpg regardless of what the scan tool says...[/align][/align]The IAC mod restricts the amount of air the IAC can flow, since this is metered airthis also means less fuel will be injected.The scan tool may be reacting to this, however it'soperatingat one of theextreme ends of its range so accuracy won't be good--and if it's telling you 0.4 or 0.8 mpg with the car stopped then it's just saying that instead of 0.0 to keepthe number of help desk callsdown... [/align][/align]I don't believe you'll see anysignificant difference, however it is an interesting exercise--let us know what you find?[/align][/align][/align][/align]

 

no no, at a stop it reads 0 MPG, and .4 GPH(gallons per hour), when stock it read .8GPH. so the scangauge to the best of my knowledge is accurate. And I do agree that since less air is being sent in, less fuel is as well, so from a logical stand point, in stop n go traffic I should get better fuel economy. BUT this morning I changed the gaskets. I put the non wollered out 3/16" in and it would not idle, but the 5/32" would(not well though) so I just put the wollererd out 3/16" in there for the simplicity of being able to use my ac and the GPH went up to .6, still better than .8

 

ok so I went for a test drive. At idle, the gauge reads .6 GPH, but the idle went from 750 to 900 RPM and idles high, no problem with that, but its weird that my GPH went down, my idle went, and the RPMs still fall fast, its the best of all three worlds....

 

Anyone have any ideas why it idles higher...? Also when I turn the AC on, the rpms drop down to around 500 and pick back up 700. Kinda low, got any ideas...? I also made the hole bigger now for the AC problem, jumped up to a wollered out 7/32". Idle is still high, 1050ish, GPH went to .7, and the AC is perfect, is this normal...?