355 New Build Idle
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Staging Lane
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From: East Liverpool, Ohio
355 New Build Idle First I'll give a little info about the new build.
355 11.7 to 1
Compstar Rods
Mahle Pistons
21 Degree LE Ported Trickflow Heads
LE Custom Cam
LE Ported Intake
Ultra Rockers
ARH 1 3/4 -1 7/8 Stepped headers and X-pipe
Performabuilt Level 2 3600 Stall
3.73 Gears
Its in a 94 Corvette. Its all together and running and drives really good but it wont idle. The throttle body is a PP 58mm. I don't know if its ok to open the throttle blades and reset the tps voltage or to drill a hole until the iac counts come in line. I haven't put it on the scanner yet but I will in the next few nights and see where its at. If you drill the hole it would seem to me that you would want to isolate that air from dumping into the plenum also. I geuss I want to see what most do and don't want to cut any corners now.
355 11.7 to 1
Compstar Rods
Mahle Pistons
21 Degree LE Ported Trickflow Heads
LE Custom Cam
LE Ported Intake
Ultra Rockers
ARH 1 3/4 -1 7/8 Stepped headers and X-pipe
Performabuilt Level 2 3600 Stall
3.73 Gears
Its in a 94 Corvette. Its all together and running and drives really good but it wont idle. The throttle body is a PP 58mm. I don't know if its ok to open the throttle blades and reset the tps voltage or to drill a hole until the iac counts come in line. I haven't put it on the scanner yet but I will in the next few nights and see where its at. If you drill the hole it would seem to me that you would want to isolate that air from dumping into the plenum also. I geuss I want to see what most do and don't want to cut any corners now.
Last edited by mobileman; Oct 12, 2011 at 03:43 PM.
Is your TPS voltage set? Alot of PP tb's require slotting the tps mounting holes to get .6v for it to idle properly. How big is the cam? Doing the IAC drill mod might be something to look into afterwards depending how big the cam is.
If it still wont idle with the tps reset i would suggest unhooking the battery to let it to fully reset itself again. Mine had this issue after i got it set to .6v it still wouldnt idle so i unplugged the battery and since then all is good.
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Staging Lane
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From: East Liverpool, Ohio
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have you had the PCM tuned for this new motor?
use a scan tool to read IAC counts. With the 58 mm I suspect they are high and the "drill" mod is in order. The other alternative to drill mod is slot TPS holes and "slightly" crack TB blades. My $02 is drill mod
assumeing you have a tune you could throw on the stock TB to see if that makes the idle right. That would then clearly show the 58 is the source of idle problem and not tune.
use a scan tool to read IAC counts. With the 58 mm I suspect they are high and the "drill" mod is in order. The other alternative to drill mod is slot TPS holes and "slightly" crack TB blades. My $02 is drill mod
assumeing you have a tune you could throw on the stock TB to see if that makes the idle right. That would then clearly show the 58 is the source of idle problem and not tune.
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Launching!
Joined: Mar 2009
Posts: 274
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From: Weatherford Tx 76085 corner of N. Hwy 51 and 150 Green branch Rd.
I had the same problem with idle with a holley throttle body "no hole in it", once I drilled the hole for the IAC it ran great. I drilled the hole a little bigger than the factory throttle body.
I have yet to do the drill mod on my prof prod 58mm it doesnt have idling issues when first started but coming to stops the idle will drop to 4-500rpm and bounce back a time or two. Sometimes it will stall out but not often. Will doing this drill mod correct this?
If you have a laptop and PCM cable you can set the TPS and throttle opening with the car running, get the correct number of counts at idle (around 20) and all these problems will go away. I tried for several months to get the idle right. Once I have visibility of the IAC with the car running it only took about 10 minutes to get it dead nuts on. I wouldn't do it any other way on a modified car honestly.
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Staging Lane
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From: East Liverpool, Ohio
Iac count is 160. The TPS voltage was right on so I guess I'll drill it tonite and see if I can get them to come down. I think I might need a lt4 knock module also because when I rev it up I have knock count and its retarding the timing.
Launching!
Joined: Mar 2009
Posts: 274
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From: Weatherford Tx 76085 corner of N. Hwy 51 and 150 Green branch Rd.
trust me drill it and you will notice immediately a big difference. I had the same thing with mine, it would idle just fine when it first would start but once I started moving and stop and go it would just die on me. The IAC counts were high on mine as well once I drilled the hole out they dropped way down and now I have no problems driving, even with the a/c on.
Thread Starter
Staging Lane
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From: East Liverpool, Ohio
Drilled to 17/64 so far Iac count is in the high 50s and the idle is great now. I wiil tune it in better later. I also found I was using the wrong throttle bracket and was only getting about 80% throttle. I haven't ran it hard yet but I stepped on it a few times before and was surprised how strong it was breaking traction in the 30's now its sick. I ll try to post a video of it idling.
Launching!
Joined: Mar 2009
Posts: 274
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From: Weatherford Tx 76085 corner of N. Hwy 51 and 150 Green branch Rd.
awesome! I have a fairly larger sized drilled hole compared to the factory throttle body for the cam I'm running. I had so much trouble before on mine I just started hating my car instead of enjoying it, then one day I noticed it didn't have a hole and presto been 
great ever since. Ernest
great ever since. Ernest Thread Starter
Staging Lane
iTrader: (7)
Joined: Sep 2009
Posts: 52
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From: East Liverpool, Ohio
