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Intake swap...now High Idle

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Old 05-28-2005, 05:03 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
Intake swap...now High Idle

like it says...I FINALLY swapped my intake (tbi) to a holly carb style intake and now the car idles at like 2500 rpm.

I havent really checked anything......since I gave up on her today after having to "fabricate/alter/create more or less everything for this intake" I dont know how many things for this intake. But any ideas as to where I should start for the cause of the High idle?
I am thinking the following...
1) IAC
2) TPS
3) maybe a vaccume leak around the TBI/spacer?

Can anyone provide me with any other experiences/advise?

Does the IAC or TPS have to be "reset" after swapping from a stock manifold to a Carb intake??? I wouldnt think so...but thought I would see what you guys have to say.

Thanks,
Dave
Old 05-28-2005, 07:11 PM
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I would say you have a bad vacuum leak. Spray all the sealing areas on the intake and tbi with wd40 or carb cleaner, you'll be able to tell when you find a leak. You may have more than one.

Steve
Old 05-28-2005, 07:57 PM
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Originally posted by steve8586iroc
I would say you have a bad vacuum leak. Spray all the sealing areas on the intake and tbi with wd40 or carb cleaner, you'll be able to tell when you find a leak. You may have more than one.

Steve
That was my first thought too.
Very probably more than one leak.
Keep us posted.
Old 05-28-2005, 09:21 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
Ya I am hoping that is the problem...that would be the easiest. If there was a vaccume leak...when you spray it with carb cleaner I am assuming the engine would "drop" as is sucks it in....no? The more that I think of it the more I think its the gasket between the mainfold and the spacer/adapter, I used the cheepie which came with the spacer/adapter.

I am going to look at it in the morning....I am beat from fabbing up that manifold today it was a bit of a "bear"

I will post my outcome tomorrow.

D
Old 05-28-2005, 10:39 PM
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Originally posted by tanager11....when you spray it with carb cleaner I am assuming the engine would "drop" as is sucks it in, no?
The engine will do just the opposite, it will speed up momentarily...
Old 05-28-2005, 11:26 PM
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Car: 88 Camaro SC
Engine: SFI'd 350
Transmission: TKO 500
Axle/Gears: 9-bolt w/ 3.23's
Check the throttle cable as well. The tbi might not be right where it was before so the throttle cable may at the limits of its travel and holding the throttle open.
Old 05-29-2005, 06:28 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
Well...I looked at it up and down today...and finally decided to say 'screw it..the old one is going back on...atleast I know it will run with that one on there".

So when I had it all appart I noticed the gasket which came with my spacer wasnt covering the entire TB surface. there was a "gap" on one part of it right by the throttle return spring...regardless I took the 'long way" cuz I wanted to be certain, I put the old intake back on...hooked it all up and it started/idled the way it should. Once that was all good I thought I would try the new one AGAIn wiht a new/correct gasket and bingo...she started up fine, still idled a bit high (but vs. what it was I was MORE than happy...but I think it will drop a bit more once things sorta work together/reset).

Timing is off but its all good by me..I will take care of that...I think I am well on my way with this one.

D
Old 05-29-2005, 07:23 PM
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Originally posted by tanager11....still idled a bit high.
How high?
Old 05-29-2005, 07:30 PM
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Car: 91 Camaro RS Convertible
Engine: 305 TBI
Transmission: 5-Speed
Axle/Gears: 3.42
Good to hear you got it straightened out. What intake did you go with? Don't worry about a little change in drivability or idle quality either if it's nothing major, because the change in plenum volume can surprisingly throw the tune off quite a bit. Mine took a good amount of fueling changes and timing addition/smoothing in certain areas after I put on the Holley intake.

Are you burning chips for it now?
Old 05-29-2005, 08:01 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
She is idling at about 1200 just off a couple start ups and shut downs....I havent run her all that much (maybe less than 1 min).

The inake is a holley 300-64

As for chip burning....I havent gotten into it as of yet...I will be in a couple weeks/maybe a month.....its been a long time comming but I grabbed an extra ECM which I am going to have the prominator installed into....once that happens I am going to let the "chip burning" begin....I need it......she only runs mid 15's on the stock tune and Has A LOT more in her....

D

Last edited by tanager11; 05-29-2005 at 08:07 PM.
Old 05-29-2005, 08:25 PM
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Originally posted by tanager11.She is idling at about 1200 just off a couple start ups and shut downs...
She's idling at 1200, warm?

Originally posted by tanager11.As for chip burning. I havent gotten into it as of yet. I will be in a couple weeks/maybe a month.
Make sure you read TRAXION's tech article on chip burning. I am still in absolute awe at exactly how much I learned in one freaking night thanks to him...
Old 05-29-2005, 09:16 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
ya she is idling at 1200 more less or cold...so I figure once she warms up she will drop down.

Ya I read that article...I have been reading for about a year now....its time for me to hop on and enjoy the ride of chip burning.

Last edited by tanager11; 05-29-2005 at 09:42 PM.
Old 05-30-2005, 06:43 PM
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You need to set the timing to have the car run right. What did you set the base at when the new intake was on? Are you sure the TBI unit closed all the way after the linkage was hooked up?
Old 05-31-2005, 02:50 PM
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the gasket i received with my carb/TB adapter did not fit my GM TB. it was too small at one corner near the IAC passages. i will assume it would fit a Holley? it too would have produced a massive vac leak.
Old 06-02-2005, 02:11 PM
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Car: 91 Z28 Vert
Engine: 305
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Axle/Gears: 3.55 10-bolt
Ronny...my 'problem' I believe was the same as you...i was in a rush and didnt check out the gasket shipped with the adapter....it wasnt fitting up right and resulted in a good "gap" in the surface its suppose to seal.

ShiftyCapone--> I havent set the timing yet since I pulled the distributor... I know it is probably a bit off since i pulled the distributor a couple times and "ball parked it".....she started up seemed decent...so I left it on theweekend out of pure frustration....I am going to get the light out tonight and set her. I think everything will be good once I get her dialed in. (throttle blades are fine)

I think things will be fine once I get that timing dialed in.

D
Old 06-02-2005, 04:45 PM
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i spent mucho $$ and bought the delco gasket. vac leaks are a pain.
Old 06-02-2005, 06:14 PM
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Originally posted by tanager11


ShiftyCapone--> I havent set the timing yet since I pulled the distributor... I know it is probably a bit off since i pulled the distributor a couple times and "ball parked it".....she started up seemed decent...so I left it on theweekend out of pure frustration....I am going to get the light out tonight and set her. I think everything will be good once I get her dialed in. (throttle blades are fine)


D
Good call. You need to have your timing set. The ECM can only compensate so much when the base is off.
Old 06-02-2005, 09:39 PM
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Car: 91 Z28 Vert
Engine: 305
Transmission: TKO
Axle/Gears: 3.55 10-bolt
you know what...I had a HUGE setback tonight...now I am baffled.

When I set the timing at 0 she seems fine (idles at about 1200 when warm)...but when I plug the EST (I think its called that) back in she idles really high again...I am sorta kinda interpreting that the computer doesnt like the intake. Regardless I am putting the stocker back on her and going to focus on tuning...once I understand tuning I will toss the intake back on and probably be in a better position to work iwth it.

D
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