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Old 07-21-2007, 10:09 PM   #1
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Default Idle speed problem after IC install

So I installed my IC two weekends back and at first just noticed that the car was idling a little high, like 1K rpm, I figured it was because of my IAC tube routing and didn't worry about it.

Since my hot pipe goes over the radiator, and my cold pipe goes around and up to the TB I just ran the hose from the IAC across the engine to a tube I welded on to the hot pipe, it seemed like the simplest way to go about it.

I should also note that my car has always had trouble with warm starts (even when it was stock), and with the old crossover pipe setup it used to idle a bit low, like 750rpm.

The problem seems to have gotten worse though. Now, once the car is fully heat soaked it will idle close to 1500rpm. I can get it to drop a little by loading the electrical system (fan, lights, windows...)

If I choke off the IAC hose it drops down to 800-900 rpm, right where it should be.

My car is a 94, resistance across the two pins in the IAC is 13.1 ohm.

Do you think this is a sraight IAC problem or related to my pipe routing?

Meanwhile I am planing to go to the gap next weekend and I don't know if I can fix this properly before then. Any ideas for a quick fix?

As long as it stays warm I can probably block the hose off, or maybe just live with it, I am not sure how bad that high idle is and if it will overtax my cooling system.
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Old 07-21-2007, 11:47 PM   #2
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I have my aic routed back in right in between the i.c. coldside outlet and the t.b. inlet. I'm not sure if it matters how far away from the t.b you route the aic back in but, i don't think that would affect too much negatively if you did route the aic back in on the hotside of the i.c.

sounds to me like you just have an aic issue if pinching off the hose completely, gives you correct idle
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Old 07-21-2007, 11:56 PM   #3
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I wonder if the pressure drop from the inetercooler affects it the IAC doesn't need much air to idle the car.
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Old 07-22-2007, 05:52 PM   #4
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I decided to try the parallel fan mod, I was thinking it might lower coolant, maybe even engine bay, temps a little, reducing the temperature of the IAC, which seems to have something to do with the problem.

I think it helped. Now when I come to a stop the idle drops to about 750, then quickly climbs up to about 1600, then after about 60 seconds it drops to like 1300, then after anouther minute it drops to more like 1100. I can't really be sure if this is from alternator drag due to running both fans, or because lower temps are helping the IAC to work, but if it stays the way it is I can live with it for a while.

I don't think there is any pressure drop through the IC at idle, but I suppose the IAC will see higher pressure on the upstream side under boost, I wonder if that could be messing with my already marginal IAC. I should probably pull it and try to clean it out, but I know its going to take a week to get the gaskets.
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Old 07-23-2007, 11:03 AM   #5
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clean it out.

I had one go crazy onme once and it was the IAC unit that went bad. I could not get the car to hold a steady idle. It would almost die coming to a stop or it would bounce like you say. Like I said try cleaning it out (spray some carb cleaner in there) and if that does not work try a friends or a junkyard part.
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Old 07-23-2007, 06:26 PM   #6
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I ordered a gasket for it, supposed to have it on Wednesday, hopefully cleaning it will do the trick. $10 for the stupid gasket.
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Old 07-23-2007, 09:55 PM   #7
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I dunno, it sounds like a vacuum leak....how's the BOV... VTA?
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Old 07-23-2007, 10:24 PM   #8
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No, its recirculated, thing is the behavior is not all that consistent, I can let it sit in the driveway and idle for an hour and it will idle just fine, but go for a drive and after a while it will start doing this. If I unplug or block off the IAC it idles perfectly, but dips too low if I turn on a bunch of accessories. Nonetheless, I will check for vacuum leaks.
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Old 07-24-2007, 01:20 AM   #9
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Quote:
Originally Posted by Mechazawa View Post
No, its recirculated, thing is the behavior is not all that consistent, I can let it sit in the driveway and idle for an hour and it will idle just fine, but go for a drive and after a while it will start doing this. If I unplug or block off the IAC it idles perfectly, but dips too low if I turn on a bunch of accessories. Nonetheless, I will check for vacuum leaks.
sounds exactly like mine did.

Try this when it starts going crazy try popping the hood open and unplugging the IAC. See if that smooths the oscillation.
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