jishead

FYI: Some Mustang TB's have a hole in the butterfly and some don't? I P&P'd one from E-bay and installed it last night. Idle is crazy even after turning the screw and verifying the TPS. Bottom line: My original butterfly did NOT have a hole to allow extra air in at idle and the Ebay OEM butterfly does so my computer and IAC and system in general are now getting too much air. I'll try and block the IAC off even more to compensate and hope that I don't run to rich. Though I'd post this FYI for any other do-it-yourselfers.

Acer2428

Yeah, my MAC has one and I freaked out too.... The orig owner had some type of mettalic tape over the hole. I took it off and all is well.

jishead

I thought about plugging the hole at least temporarily with tape or whatever but am nervous about putting anything near that TB throat that could come loose. That metalic tape sticks well and holds up to temp extremes though I guess.

tomabram

did you try to reset the base idle?

jishead

I tried turning that screw thing that sets the butterfly more closed and that did help a tiny bit. I checked the Predator and it is still programed for 680 or whatever it always is. Yeah, the problem is that it's getting more air through the butterfly now in addition to the air it gets from the IAC, breathers or PCV and whatever. I will experiment today and take it on a long trip to my friend's house.

tomabram

By just turning the screw wont set the base idle. You have to disconnect the IAC motor than set the idle as low as it can go without stalling, about 500rpms. Then disconnect the battery for 30 minutes. Reconnect the IAC and battery then start her up. I would try this first.

jdaniel

Actually you need to disconnect the IAC Bypass plug and set the idle to 600 rpms and when you plug it back it the rpms should kick up to 750-800. When you unplug it the car should either almost die or idle up depending on how the base idle is set with the new throttle body.

tomabram

No, what I said was correct. If you dont disconnect the battery to reset the computer your wasting your time beacuse just disconnecting the IAC WONT reset the base idle. Plus you have to set the idle as LOW as possible. If you can get it to 400 without it stalling great.

Acer2428

OR, you can back out the idle screw all the way, reset the computer and hope for the best. worked for me.

tomabram

Yeah but when you back out the idle screw all the way the butterfly catches on the TB.