Throttle Bodies

Vettn71 · Aug 1, 2016

Have a 96 GT, worked over 4.6 with a 0.20 over Cobra aluminum block. I have a C&L plenum, BBK 75mm throttle body, Competition Cams 268 cams, 10.5:1 compression (9cc dish), PI heads (with some pocket porting) and intake, three-angle valve job, stock exhaust manifolds and an AirRaid CAI. I know all this isn't necessary, but someone is bound to ask. I just had this thing tuned and it put down 298 to the rear wheels; not bad. My goal was 300, The tuner, Travis at GearHeads, said he pulled some timing because I had bad gas. I'm okay with that. As far as I see it I made my goal. Oh, yeah, this is a 5-speed car with 3:73s.

my question is about throttle bodies. I keep reading how the BBK is not so good, both in quality and performance, especially idle quality. I am having some issues getting it to idle down. Travis recommended dropping the idle speed using the idle adjusting screw, but when i get the idle lower than 1,000 rpms, it tends to die. The idle also hangs pretty bad. It will go to 2,000 when I pull up to a light, then 1500, then to its final idle. I've got it where it doesn't die on me, at least. I know hanging idle is one of the characteristics of the 4.6, but mine takes a loooooong time.

Would an an accufab throttle body help?

TIA

Jim

Frank.JD.Perez · Aug 1, 2016

ive got the 78mm combo and i dont have any issues, bbk is a fairly good brand though but if it were up to me i would go with the best in the business which i cant tell you who that is cause i have no idea

07GtS197 · Aug 2, 2016

Im having the same problem with my throttle body. Im trying to sort my issue out with resetting my ecu but Im not so sure thatll help.

Nighttrain · Aug 2, 2016

Its not the tb. Make up a iac restrictor plate. It goes between the iac and the tb. There is an article already here somewhere on it. I think its under common 2v problems. Anyway start with a 3/16 hole and work up from there. You shouldnt have to go any bigger than 3/8 i think, but every car is a little different. It restricts the air to the valve lowering you idle and stopping the hanging. You can use gasket material to do this. Fairly easy and straight forward.

Vettn71 · Aug 2, 2016

I appreciate the replies. I've seen two ways to do the IAC restrictor; one using the gasket and one using a half-inch copper cap with a hole drilled in it. Does one work better than the other? Does this cause other issues? Seems this could be tuned out, but so far that's not the case

Jim

07GtS197 · Aug 3, 2016

A lot of the crown vic guys use the copper cap mod to bring their idle down when first starting the car. The more simple approach would be to flip the gasket around and cut another hold smaller in diameter. You might want to look at the stock iac gasket but from what I remember it has a hole on the right side and nothing on the other. I just ordered a restrictor plate to be done but in retrospect I could have done it for free with the gasket... Oh well it was 6 bucks lol.

Nighttrain · Aug 4, 2016

Vettn71 said:
I appreciate the replies. I've seen two ways to do the IAC restrictor; one using the gasket and one using a half-inch copper cap with a hole drilled in it. Does one work better than the other? Does this cause other issues? Seems this could be tuned out, but so far that's not the case

Jim

Ive seen both ways to i find the gasket to be a little easier, especially trying to get the hole just right instead of digging the cap out each time. The iac problem wont get tuned out because its still reading a certain amount of air then communicating that to the ecu, not the other way around. Think of a wideband o2, and a narrowband. Cant communicate with a one way sensor............sounds right in my head but i hope you know what im talking about.

Jakespeeds · Aug 4, 2016

I have a mildly modded 98 with an iron block 4.6 and PI swap. I have the full BKK intake setup including the MAF. The only part I had bought used was the throttle body and intake elbow. My idle used to hang what I thought was too much but this was my first Mustang with a mod engine. After going through everything multiple times I bought the one piece BBK throttle body intake elbow 78mm part. Nothing changed. The car already had a custom full chassis tune and they had tweaked it out as much as possible. Maybe yours is worse than mine. But I have gotten used to it and don't even notice it anymore. I have been told by a few people that are more familiar with these engines that what I have is real good as far as the idle hang. But unless you have monkeyed with the idle adjustment screw I have seen nothing to think there is anything wrong with BBK equipment. You may want to address that all the components are well matched. An air velocity change in the intake track will affect the idle hang as well.

Jake

ttocs · Aug 4, 2016

I am not familiar with mod motors but the pushrods have the same problem and it always seems to be after the throttle body install. Is there something like this for the mod motors as this is what I used to dial mine in?
https://lmr.com/item/LRS-9939A/1986...er?year=1993&gclid=CMahtZjSqM4CFREoaQodO8EIOQ