Folks, one of the more common and relatively cheap mods is a TB upgrade. All of us eventually seem to get around to this mod. However, there is a rash of reported idle problems after doing this.

I am writing this thread to help some of you who may run into problems. There are a few things that you can do to avoid challenges and be a happier user. This is a great mod and should not be avoided becuase of idle issues than can be easily corrected.

All my comments are for a 4.6 stock motor w/o power adder, but these helpful tidbits may be useful to everyone.

1 - A Throttle Body (TB) upgrade only seems to be useful when adding an aftermarket plenum. The combos are good for 10 - 14 rwhp and gains are evident throughout the power range.

2 - Use either a 70 mm or 75 TB...nothing bigger. The actual selection of size should be based on the type of plenum used. With a C&L use a 75 mm for example.

3 - Before installing the TB, hold it up to a light source and make sure the TB blade is closing completely. If not, you will have poor idle issues. You should not see any light through the blade when THE TB IS COMPLETELY CLOSED.

4 - Be prepared to purchase a new Throttle Position Sensor (TPS). The stock ones are difficult to remove and they can get damaged when taking them off. Seems like a slight jarring of the TPS will mess it up. TPS's can be purchased or $25 at Pep Boys. I think it is money well spent to just buy a new one unless the car is brand new.

5 - Clean the Idle Air Controller (IAC) when you have the stock plenum off. Many idle problems have been reported after a TB/plenum swap due to a dirty IAC. A dirty IAC will become more pronounced after the swap as the new TB opening is larger, so more air is allowed in at the same throttle opening. Use intake cleaner that is approved for TB's. If not, you can corrode the TB blade.

6 - When you have the car put back together, reset your fuel trims by dissonnecting the battery. Then, start the car. Let it warm up. The car should idle like a dream, perhaps a little lower than what you are used to.

7 - If you have problems, or you want to be sure the idle setting is correct, with the car runnning, disconnect the wire harness to the IAC. This will force the IAC closed. When this occurs, the car should still idle, but act like it is going to die. If it does not do this, then the idle set screw needs to be adjust slowly so that the TB is forced closed a little futher. If the car immediately dies, then you need to open the set screw up a tad. Removing the harness will result in an SES light within a minute or so. You will need to clear the code with a programmer or by disconnecting the battery again.

Hope this info is useful. Please chime in if you have experience with this swap.

 

Do you have any experience with Accufab TB/Plenum setup? Does getting a bigger TB/Plenum setup effect MPG much +/-?

 

I don't have any personal experience with the Accufab as I used C&L. However, I would not hesitate to use their stuff. I can't imagine any of the TB's or Plenum combos affecting mpg by much at all. Any mod that produces more hp runs the potential of using more fuel, but with a mod that gains 10 10 15 rwhp, the additonal fuel consumption should be extremely minor.

 

I have heard also to get the car dyno tuned immediatly after the TB/Plenum combo...true or not true?

If true, would a hand-held programmer like the Predator handle this?

 

I don't buy that for a minute. Keep in mind that your car is somewhat self-tuning. The ECU constantly monitors the o2 sensors and controls how much fuel is added.

The Predator offers some very limited control of timing and fuel curves, so when combined with a wide-band and a data logger, a Predator owner can tune their own car somewhat.

Don't worry about a dyno tune with a TB and/or plenum.

 

A tune is not needed for this upgrade. A good tune would be helpful. Anytime you add intake or exhaust mod's you tend to lean out your air/fuel ratio. This actually makes more power, running a little lean is not harmful but the safest approach would be to get a tune after you do gears/intake/exhaust mod's. They can correct your speedo for gears change and firm up shift points on an automatic.
I picked up quite a bit of top end speed after my tune
went from 102-103 avg to 104-107 avg. Also cut .015 off my e.t. in the qtr. Car drives much better with the tune.
A off the shelf tune from SCT is around 325.00 for a four position chip. Or you can get the handheld tuner/flasher with a tune for 100.00 more and make some changes yourself. I drove my car for a year with no tune and had no issues. That was with the C & L plenum, 75mm TB, X-pipe w/cats, catback, gears and timming advanced manually to 14* running 93 octane. I got it tuned when I added a high stall speed torque converter and went to 4.30 gears. The tune helped out with all the changes I had made to the drive train but also cleaned up my a/f ratio and made more power which comes on faster at a lower rpm than before and pulls harder at the top end. If any of you have ever run these 2v's at the track you will feel them go flat at 5,300 rpm. This is were I would quit making power, since the tune the car pulls hard all the way to 6,000. Now those rotten LS1's can't run me down.

 

you can also get a mail order dynotuned SCT chip from www.modularpowerhouse.com for 325. Tim dyno tunes many cars and saves each file, so when you send him your mods, he will find a file that has the same mods as your car. BTW if you are worried about your car being different than others (from the factory), he told me that he didn't need a base line to work from, but instead he can just set things to where they need to be. Let me see if I can explain this better...I got my car dynoed to check the a/f ratio and it was very lean. Tim told me he doesn't need a baseline (or in my case my dyno sheet showing my a/f ratio) to set the timing and a/f ratio where it needs to be.

Also, in the case of the chip mentioned above, it is also a 4 bank chip, and Tim tunes in the ability to add up to 25 hp before you need to get it retuned.

 

the reason most people have weird idles is that they add a new TB and do not check or adjust the tps voltage. if its over 1volt it gets weird if its to low it can cause weirdness also. it needs ot be as lcose to .99 volts or on that to have a nice clean idle again. overwise cleanning IAC and other things dont mean a damn thing.

 

Dustin, I should have mentioned the voltage issue in the thread.

 

Good stuff MT#1 I like the info you are putting out here

 

Thought I'd throw this in just cause I don't contribute often!

The Accufab is the prettiest and most expensive... but it's shown to add about 2 hp over the other models available. One of the forums did some pretty extensive testing with 4 aftermarkets versus stock... running 3 pulls on each on a dyno machine.

The question becomes, when is 2 hp worth it

This will definitely be a mod I look at soon... first I have to do the gears, the underdrive pulleys and the CAI... that'll put me in position to start looking at the bigger and better things!

 

Well, you mentioned doing the CAI before the plenum, well, the CAI has been proven time and time again to do about NOTHING but make more noise. If it were me, Id just drop in a K&N filter, and then do the plenum and tb first. Save the 150-200 bucks you would spend on the intake and buy a plenum instead, just a word of advice.

 

A bit off topic, but this is an awesome CAI! Great design that makes sense.

http://www.apten-us.com/performance/gt/gtcai.asp

 

What size... 70 or 75mm? I've been told 75 is too big until you get FI... how much power will it cost me to go with the 75 in anticipation of later going with a Turbo or SC? Which size would u suggest at this point?

 

That is a pretty neat little CAI. Have you seen any dyno sheets on it? Or know of anyone who has used it before?

 

As I have told my wife, size doesn't matter.

Which size TB you use really depends on the the type of plenum. C&L performs better with a 75 mm TB.

 

No dyno data that I have been able to find, but you really can't argue about the design. Seems well engineered.

I like it becuase it draws from the fender well yet has no bends to mess with the MAF. Very similar to the stock unit, but allows more air. Also, very easy to service the filter.

I have the Steeda CAI. One nice thing about the Steeda is the bright metal (if you like the look) and the ram air affect you can get when pulling your head light out. Sure other setups offer this, but just comparing my Steeda to this one in the link.

 

That is a pretty nice looking intake, id still have to see a nice increase to justify 250 bucks.

 

well in case you do want to install the accufab 70mm tb/plenum combo and you dont know how, i made a write up that im sure people may find useful...here ya go

Click here for the Accufab Write-Up

 

that was a very nice write up. Thank you for doing it.

 

no prob. thanks for the compliment...i appreciate it

 

Wow I could have used that about 6 months ago I put a BBK 70mm on my 94 gt and it never idled the same. You sure do know alot I'll be posting some questions for you soon I'm about to start monkeying with my 04 cobra soon

 

I was planning on going with a c&l plenum and bbk throttle, i didn't know the 75mm would be okay on a near stock motor, my mods are k&n CAI (which is pretty similar in design too the one u supplied in that link), slp catted xpipe with slp catback bought from Mustang Tuning The diablosport programmer, and steeda pulleys...its an 04, so i have too worry about the tps with that or that voltage issue?

thanks
Mario

 

I just swapped over to accufab T/B and no problems yet.

 

how was the power increase, noticible? I'm planning on dynotuning mine, I used the diablosport programmer's "diablo tune" so I think I'm running a little rich, when i have the heater on the inside of my car smells like exhaust.lol better being rich then lean though

thanks
mario