Copper pipe cap mod. Didn't like it...

[Skidzz]

Hey guys I know there is an old thread somewhere on here about fixing the hanging RPM's on these cars, but I just couldn't find it.

Anyway, I decided to do the copper pipe cap mod on my IAC valve. I basically drilled the hole small at first and just kept making it bigger little by little until the car would idle without dying. The mod did exactly what it was supposed to. The RPM's dropped way quicker and the engine gargled more when I let off the gas.

I didn't like it though. It seemed more difficult to keep it in the power-band and I swear it felt like my car wasn't pulling as hard above 4k RPM's. I'm wondering if these issues have to do with my gear/cam combo? Or maybe my tune? Anyway, I changed it back to stock and I just like the way it feels better. I'm glad I only spend $0.57 on this mod.

 

[BlackStang03]

Is that how people get the RPM's to drop quickly? Where did you find the info to do this

 

[patman0911]

Interesting.

The PCM does command the IAC valve full open in a lot of situations - I wouldn't think it would make much difference if the throttle is open much at all since it's all metered air whether it goes through the IAC or the TB and the TB can pass plenty of air without the help of the IAC bypass.

It might benefit from driving around and letting the computer learn the new setup.

 

[Skidzz]

It might benefit from driving around and letting the computer learn the new setup.

I was thinking about that. I only had the mod for about a day before I took it out. But would a computer with a custom tune still have the ability to adjust?

 

[bhuff30]

Yes, the computer can still make adjustments with a custom tune.

I don't see any reason the car would feel any different at wide open throttle with the restrictor in the IAC. All airflow should flow through the throttle body anyway. I'm thinking you just don't like the way the car feels between shifts. The engine certainly would loose a lot more rpms and energy when shifting, so it will feel a bit more boggy when you get on it again. However, once you are done with the gear change and get accelerating again, there should be no difference at all in the power band.

 

[patman0911]

That's what I was thinking, I don't see how it could possibly make a difference at WOT but maybe it does in other situations which makes the car feel different enough to make you think something's off.

Mustangs do pull a lot of timing between shifts so combined with the bigger drop in RPMs, the engine may feel more sluggish than before when getting on the throttle again if the inertia of the car is trying to drag the engine's RPMs back up again instead of the inertia from the higher RPMed engine trying to drag the speed of the car up.

 

[Skidzz]

Yea I think you guys are right. I mean, the mod only restricts flow to the IAC, not the intake. My car starts to pull hard around 3k because of the cams and gears, and without the mod, my RPM's stay in the powerband when I shift, but with the mod, the RPM's drop well below that range and I have to run through to lower RPM's where the car doesn't make as much power. So, essentially, it kind of IS making the car slower, even though it's not actually reducing power.

 

[Maxpowers]

Is that how people get the RPM's to drop quickly? Where did you find the info to do this

x2

Interested in a DIY for this

 

[Skidzz]

Ok for those of you interested in the mod, you take a 1/2 inch copper pipe cap (you can buy it at Lowe's) and drill a hole in the top of it. Then you just put that in the hose that feeds air to your IAC valve. Done. You should start with a small hole and work your way up until your engine will idle on its own without dying.