Large Marge: The New Adventures

[His Royal Ghostliness]

Ah true, if the steel bit falls of it's quite unforgiving once it makes its way down into a cylinder. The pop-rivet idea would work yes, but he'll have to take the TB off, which he said he doesn't want to do.

Still, I think it's odd that just swapping to larger upper intake bumped his idle speed up so noticeably, can't recall ever experiencing that myself - for example the Doktor's Mk6 that ya'll saw at SF runs HO upper and has absolutely no issued idling nice and low. So I'm still suspecting a vacuum leak somewhere...

[gadget73]

agreed, but once in a while it does happen. Some of the HO throttle bodies had a large bleed hole that it just doesn't seem to be able to compensate for.

[Brown_Muscle]

I'll check the TPS, does the computer have a code for "part throttle" on startup for higher TPS voltage? I know there is a flag for it...or should be. I got no such code.

I know this sounds ghetto but what about JB weld? Scuff the surface and allow to harden. Its even softer than lead and can be drilled if i want to make a small hole, and I've never had adhesion problems with it...it's tough stuff.

Without knowing the IAC duty cycle there's no way to know how little, or how much the IAC is open in a stock LOPO, it could be barely open, and then with a HO TB with a MUCH larger hole is added, its got no room to close any more, and hence the idle stay higher.

[His Royal Ghostliness]

There is a pair of TPS out of range codes, low and high readings respectively. Being that KOEO test is done with the TB at its idle position, you essentially do end up with a code showing you TPS voltage discrepancies at idle. Without an IVS (that's a drive-by-wire EEC-V thing) part-throttle codes would be hard to come up with since TPS is essentially the only thing telling the ECM whether you are part-throttle or not - during KOEO it can pretty safely assume you won't be fucking with the throttle pedal, but if you were to move the pedal the ECM would have nothing to compare part-throttle TPS readings to.

If you're good at using JB weld I don't see a reason why you can't use it to close the bleed hole off.

[DerekTheGreat]

agreed, but once in a while it does happen. Some of the HO throttle bodies had a large bleed hole that it just doesn't seem to be able to compensate for.

Sorry to hijack the thread here but I've always wondered why EFI cars need bleed holes. I can understand why carbs need them as they allow for an increase in idle speed without engaging the primary venturies. But SEFI, why? Did they just not want the TB's throttle plate open that much?

[BigMerc96]

IDK why they had bleed holes either. And some did and some didn't, at least in the Modular engines. The stock 65mm TB on a '96-'04 Panther does not have a bleed hole. The stock 70mm TB in a '97-'04ish 4.6/5.4 truck motor sometimes did, sometimes didn't. I've pulled several of these from E-series vans as its a cheap upgrade for a Aero/Whale and about 1/2 of them had a bleed hole, and were otherwise identical to the ones that didn't. I seem to recall one of the ones that didn't had a brass rivet filling the hole, but I could be imagining that. The one I've used in all 3 of my cars is off a '99 E350 5.4l, it has the bleed hole, and it doesn't effect idle in the slightest once you adjust the cruise control cable so its not holding it open.

Actually, thats a good point, one of the cables isn't holding the TB open slightly is it? On an Aero/Whale when you swap in the larger TB, the cruise control cable will hold the TB open ever so slightly, just enough to raise the idle but cause no other drivability problems. This is because the cable bracket on the bigger TB is slightly larger in diameter with the stud for the CC cable slightly further out, just enough for it to interfere. Adjusting the cable where its bracketed to the plenum solves it. Dunno if box cables are adjustable or not (aside from TV cable, obviously), never messed with swapping any parts that would require messing with them.

[TecNickal]

IDK why they had bleed holes either. And some did and some didn't, at least in the Modular engines. The stock 65mm TB on a '96-'04 Panther does not have a bleed hole. The stock 70mm TB in a '97-'04ish 4.6/5.4 truck motor sometimes did, sometimes didn't. I've pulled several of these from E-series vans as its a cheap upgrade for a Aero/Whale and about 1/2 of them had a bleed hole, and were otherwise identical to the ones that didn't. I seem to recall one of the ones that didn't had a brass rivet filling the hole, but I could be imagining that. The one I've used in all 3 of my cars is off a '99 E350 5.4l, it has the bleed hole, and it doesn't effect idle in the slightest once you adjust the cruise control cable so its not holding it open.

Actually, thats a good point, one of the cables isn't holding the TB open slightly is it? On an Aero/Whale when you swap in the larger TB, the cruise control cable will hold the TB open ever so slightly, just enough to raise the idle but cause no other drivability problems. This is because the cable bracket on the bigger TB is slightly larger in diameter with the stud for the CC cable slightly further out, just enough for it to interfere. Adjusting the cable where its bracketed to the plenum solves it. Dunno if box cables are adjustable or not (aside from TV cable, obviously), never messed with swapping any parts that would require messing with them.

Didn't have any issue with the Aviator TB on my 03. Bolted, clipped on - no adjustment required.

[His Royal Ghostliness]

Dunno if box cables are adjustable or not (aside from TV cable, obviously), never messed with swapping any parts that would require messing with them.

They are adjustable, and most of them need it done by now if cruise was used often. You pop a retaining clip off, slide things in/out as needed, reinstall clip, done. Very similar to how TV cable is adjusted, but the clip is steel and external to the cable end, as opposed to plastic and internal for TV stuff.

[gadget73]

the air bleed is to add some idle control range basically. There is a minimum amount of airflow required, so the idea of the bleed hole is to provide near that and let the IAC handle the rest of it. It also helps make sure you're not icing up around the edges of the throttle blade by moving air through the middle of it instead. Probably extends operating life on the IAC too, the longer the duty cycle, the more it will be prone to heating up. Ditto the driver component within the ECM. The less it has to do, the less heat it makes.

I suspect the hole size changed somewhat to even out idle issues. Some cars had an extra geegaw installed between the IAC and the throttle body that was basically just an adjustable air bleed hole. It was used to correct surging idle issues. I don't have any data to back this up, but I half suspect the cars with the geegaw and the idle problems may have had the small air bleed hole in the throttle body.

[87gtVIC]

When I did the HO upper with throttle body eons ago my idle was raised. I did have a bleed hole in the throttle body blade. I popped in one of those plastic anchors you would set into drywall and then run a screw through it. I did not add a screw. Plastic anchor was enough. worked for me.

[BigMerc96]

They are adjustable, and most of them need it done by now if cruise was used often. You pop a retaining clip off, slide things in/out as needed, reinstall clip, done. Very similar to how TV cable is adjusted, but the clip is steel and external to the cable end, as opposed to plastic and internal for TV stuff.

So, exactly the same as a 4.6 then. Remove the clip, slide the cable a bit, reinstall clip. Funny how so much is totally different yet exactly the same thru the generations of these cars.

[His Royal Ghostliness]

When I did the HO upper with throttle body eons ago my idle was raised. I did have a bleed hole in the throttle body blade. I popped in one of those plastic anchors you would set into drywall and then run a screw through it. I did not add a screw. Plastic anchor was enough. worked for me.

^^^ Phil, do this! It's dirt cheap, and IF it falls out it won't hurt anything while it's "processed" by the engine.

So, exactly the same as a 4.6 then. Remove the clip, slide the cable a bit, reinstall clip. Funny how so much is totally different yet exactly the same thru the generations of these cars.

Hey, if it works there's no need to mess with it.

[Brown_Muscle]

What a great convo, I'd like to add apparently mustangs had at least 2 different air bleed hole sizes, mine has the larger one. I have a million plastic drywall anchors, so I'll give that a go. I'll also make sure the throttle/cruise cable isnt holding it open at all.

The car is thoroughly inoperative now. No front brakes, and the engine is down to the timing cover.

Question, did these later models come with a rubberized oil pan gasket? That appears to be what mine has

[gadget73]

at some point it went to that. My 91 Mark VII has one. Not sure when the changeover was

[DerekTheGreat]

the air bleed is to add some idle control range basically. There is a minimum amount of airflow required, so the idea of the bleed hole is to provide near that and let the IAC handle the rest of it. It also helps make sure you're not icing up around the edges of the throttle blade by moving air through the middle of it instead. Probably extends operating life on the IAC too, the longer the duty cycle, the more it will be prone to heating up. Ditto the driver component within the ECM. The less it has to do, the less heat it makes.

I suspect the hole size changed somewhat to even out idle issues. Some cars had an extra geegaw installed between the IAC and the throttle body that was basically just an adjustable air bleed hole. It was used to correct surging idle issues. I don't have any data to back this up, but I half suspect the cars with the geegaw and the idle problems may have had the small air bleed hole in the throttle body.

Thanks for the explanation, makes sense!