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Old 09-06-2005, 08:49 PM   #1
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High IAC and Low idle only in Drive/Reverse

Not sure what the heck is happening.

In Park, the car Idles fine... good enough for a lumpy Cam anyways.
The IAC's are normal.

I put the car in drive or reverse... and the IAC's max out at 160 (on Scanmaster) and the car searches for idle... and drops really low and surges... if I wait too long, the car will die.

No driveability issues... car runs strong with no sputtering, etc. at any other speed... even IAC's drop once the car gets going.... only problem is idle.

I've searched the board with no answers.... so I thought I'd post to see if anyone knows what the heck is happening.

BTW, the car has the LTCC ignition and a Edelbrock 58mm TB... not sure if it makes any difference.

Thanks in advance for your help guys.
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Last edited by C Man; 09-07-2005 at 07:02 AM.
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Old 09-07-2005, 07:03 AM   #2
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Re: High IAC and Low idle only in Drive/Reverse

Just thinking of solutions.... does anyone know if our tranny has any sort of vacuum actuator of some sort that only works when the car is in gear?
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Old 09-10-2005, 09:11 PM   #3
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Re: High IAC and Low idle only in Drive/Reverse

I'm thinking that I'm not loosing vacuum... but adding a load on the car when in Drive/Reverse.

I have opened up the TB Blade a litte by adjusting the screw..... IAC's remain pretty high in Drive but the car doesn't stall. However, the idle in Drive with the foot on the brake, still surges/drops, etc. It actually drops pretty low... than "Catches" itself... for a little bit.. than surges.

When putting it back in Park ... the car revs a little while the IAC adjusts... then idles perfectly fine.

Anyone else have this problem? Could it be the 58mm TB. Is it the LTCC ignition system? The car runs great other than this problem.
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Old 09-10-2005, 10:52 PM   #4
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Re: High IAC and Low idle only in Drive/Reverse

I would say it is the load when it is put in gear. How was the tune altered for your mods?
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Old 09-11-2005, 06:45 AM   #5
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Re: High IAC and Low idle only in Drive/Reverse

i seem to remember some people needing to drill the bleed hole larger in that throttle body, the problem was that the IAC couldn't compensate enough, the IAC steps at 160 means it is trying to get more air in there but couldn't
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Old 09-11-2005, 09:34 PM   #6
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Re: High IAC and Low idle only in Drive/Reverse

Quote:
Originally Posted by shoebox
I would say it is the load when it is put in gear. How was the tune altered for your mods?
I'm not sure "how" it was tuned... but I did get it Dynotuned after the 383.. but not after the 58mm TB install.

I did get a hole drilled... but even opening the TB Blades more doesn't help too much more... so would a bigger hole make a difference?

Do you think the abrnormally high IAC values may indicate a Vacuum leak? Maybe the car is running lean because of Vacuum... fuel added in to compensate, and then needs more air.. etc.
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Old 09-11-2005, 11:15 PM   #7
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Re: High IAC and Low idle only in Drive/Reverse

If you had a vacuum leak the counts would be lower, because it would not need as much air.
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Old 09-17-2005, 03:10 PM   #8
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Re: High IAC and Low idle only in Drive/Reverse

What do you think it could be then... it only happens in Drive/Reverse... with the foot on the brake.... if I just let the foot off the brake, the car will move forward... and there aren't any problems.

Foot on the brake in Park/Neutral has no issue.
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Old 09-17-2005, 03:17 PM   #9
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Re: High IAC and Low idle only in Drive/Reverse

try this, create a vacuum leak, pull off one of the small vac lines on the intake(not the one to the fpr), see what happens to the iac counts and how it runs
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Old 09-21-2005, 10:15 PM   #10
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Re: High IAC and Low idle only in Drive/Reverse

I think I have found the problem.

When I removed the Brake Vacuum hose and plugged it, the problem went away.

It seems that when the engine is under load and the brakes have to "work" to stop the car from moving, at low Idle, the brakes are sucking the vacuum and causing a problem.

I may have to invest in a Vacuum Reserve Canister... but before that, are there any "tricks" to minimize the issues associated with this problem? ie. would lowering or raising the idle in Drive, or changing the timing, etc. improve the brakes and vacuum enough to avoid getting a Vacuum Reserve Canister?
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Old 09-21-2005, 10:15 PM
 
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