xxxhp

Iam done installing MTI 422 motor on my 2001 C5 (A4).
The cam specs are 244/244 114 LSA

Iam currently using a PCM with Ed Wright tunning & I asked him to set the idle at 1200 rpm, but it is not happening. If I give it some gas the motor will settle down at around 1200 rpm & anywhere below that it will surge & shake. Note that Iam using the stock untouched throttle body. I know trying to get such cam to idle with a stock TB sounds stupid.

I'll appreciate any help on how & how much porting/drilling to the TB is required & whether if that would be beneficial to improve the idle a little bit.

Thanks in Advance

<img border="0" title="" alt="[Sad]" src="gr_sad.gif" /> <img border="0" title="" alt="[Sad]" src="gr_sad.gif" /> <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

<small>[ June 01, 2002, 09:35 AM: Message edited by: xxxhp ]</small>

WeatherGuy

Porting the throttle body is going to help some, but you may also need some more computer tuning on it.Though I have a bit smaller of a cam, it took a ported throttle body and two iterations with LS1 edit to get it to where it is now. The car idle is completely tame now.

I will let someone who is more up on the specifics fill you in on the precise details.

Fulton 1

iTrader: (9)

Unfortunately I don't have experience with an LS1 of your caliber, but I would start by AutoTapping it and noting where the IAC counts are. Once the engine is warmed up they should settle down around 35 or less. If your IAC counts are high then enlarging the TB hole should help. The procedure for this is to enlarge the stock TB hole in 1/32" - 1/16" increments, reset PCM, and monitor IAC counts until you get them down under 35. You may choose to drop them more, but just don't go too far because IAC = 0 will set a code.

Hope that helps <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

WILWAXU

iTrader: (6)

You get more help for this in the Tuning & internal sections.

Moving a copy of this to both of those sections.

<small>[ June 01, 2002, 02:04 PM: Message edited by: WILWAXU ]</small>

Nickn20

did you drill your TB hole to a bigger size? most people drill thiers out to 13/64....I have done this for a few cammed cars and a 422

<small>[ June 01, 2002, 02:51 PM: Message edited by: Nickn20 ]</small>

Pro Stock John

iTrader: (34)

I am running a very similar cam in my ARE 422ci IRON and I am running two holes drilled in the TB.

Surging is due to needing more air.

I'd Autotap or TechII and open up the hole until you get to 50 on the IAC or lower. Anything over 100 means it just about pegged out. I've sometimes had my IAC at 50-80 but around 75 or more it gets fussy.

I have my car idling at 1100 in drive I wish it was 900.

Nine Ball

iTrader: (38)

Drill a hole in your TB blade. Your engine is suffocating.

Tony

xxxhp

Thanks all for the replys.

Where in the TB blade is best to drill & what size to start with? Should I drill a new hole in the TB blade or just enlarge the existing hole?

<small>[ June 01, 2002, 03:54 PM: Message edited by: xxxhp ]</small>

Toxic Texan

You already have a hole in the TB, you are just enlarging it.

Pro Stock John

iTrader: (34)

I'd enlarge the existing hole.

I would not go overboard with the drilling.

If you want to be supercautious, you can drill it out and then drive it like that for a day or two.

Colonel

One note on drilling for lower pintel position counts...

Do this only with the engine FULLY warmed. The counts will get lower as the engine warms so if you set the pintel count at, say, 20 with the engine cold then you may reach 0 with the engine fully warmed. Hard to make the hole smaller.

Pro Stock John

iTrader: (34)

Good point Sandman, I was gonna say that you'd want to drill for optimal idle quality when the car is warmed up. Car will run a bit more rich at idle.

PaiN

I have similar setup... My TB hols monstorous, and still have surge issues. I think I need to up the hole, and up the idle on the pcm side.

Also I always find it best to reset the IAC motor plunger, but GM does not recommend this because you can strip the worm gears inside it.

Pro Stock John

iTrader: (34)

Larry you also have a huge PIPE. And you made us look at it! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

I can't recall, but I might have two holes, each the size of a #2 pencil.

I can measure when I get back on Wednesday from OR.

-Joseph-

iTrader: (12)

I don't think C5's had a throttle hole to begin with. On that note, there is no IAC motor either. I haven't had to check any for idle problems, but what would the scanner show for IAC counts?

Mike Norris

iTrader: (10)

Hey All,

-Joseph- is correct about the C5 TB no having a hole or IAC counts. You can start with a small hole, 3/16" or so, in the same place as an F-body, about 1/2" up from the bottom. You read the actual throttle angle and try to get it in the 3-5% area at operating temps. This is what the C5 uses instead of IAC counts.

Good Luck. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Mike

PaiN

good tips Joseph, and Mike!

Thanks

jmX

DOH, wish I'd seen this earlier. Definitly no IAC on the C5...its all electronically controlled throttle baby, yeah! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Seems like the opening angle of the TB blade would be changable via programming to allow more air in at idle, rather than having to drill a hole in the blade.

xxxhp

Hi all,

I did drill a 15/64" hole in the TB & so far it is working. It idles at about 1100rpm in Park & 800 in Drive.

MelloYellow

Drilling holes on my C5 Throttle Body made things worse. I actually ended up replacing the blade with holes in it.

We did have good luck adjusting the minimum idle stop set screw on the C5 TB tho. I think it's on the bottom. It's covered by something you have to pry off to get at.