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Idle Issue

Not sure how to search for this symptom...tried sort of a generic "idle" search but didn't come up with this one...

Idle is rock steady. But ever since it got cold around here it idles at 2K when cold and won't go below 1500 when driving unless I come to a full stop...and even then it takes four or five seconds or more to drop down to a nice steady 850 RPM. I had the idle set just fine a few months ago (using correct procedure). Anybody else seen this?
 

s_firestone

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Joined
Jun 27, 2002
Messages
1,610
Location
Park City, UT USA
Mine is doing this too. I have the FIAV blocked but the ISC working, rebuilt TB, ABS unplugged at the front plug under the coolant bottle. Jeff said it may be related to keeping vacuum up. Mine is only about 1200RPM. I don't recall it happening until I replaced the TB. I wonder if it could be the fuel pressure regulator solenoid removal. I disconnected mine about the same time.
 

atc250r

Staff member
Joined
Sep 11, 2003
Messages
13,235
Location
Orange County, NY
When the t-stat started sticking open on mine it would act up after driving a little in the cold weather. It seems that the coolant was getting cold enough to allow the FIAV to open a bit. However it sounds like you may have improperly disconnected the ABS instead.

Stephen, check to make sure your TB gasket isn't on wrong. It fits 4 different ways but only one of them will seal without an air leak that'll cause a high idle. Don't ask how I know. /ubbthreads/images/graemlins/bawling.gif

John
 

s_firestone

Well-known member
Joined
Jun 27, 2002
Messages
1,610
Location
Park City, UT USA
I verified that gasket is on right. I personally lapped the surfaces of the throttle body flat while I was rebuilding. BISS and O-Ring are new as well. My idle is 825 to 850 at a stop when the car is warm, no surging. I also would not be surprised if my old coolant sensor is out of whack, the car could be in warmup mode even though the logger registers the proper temps. I wish I could see that parameter on the logger.

My ABS is disconnected at the front connector and the 60A fuse.

Funny symptom is that the engine will idle up steady as you please when rolling(speed sensor) but the AC idle up will slowly drop from 1300 back down to 700 then up to 800 when stopped. If I try to adjust the BISS up any I hit the typical motorboat idle from the ECU trying to adjust when rolling which settles down as soon as the car stops. TPS measures 10.1% on the logger. It's consistent and repeatable.

I suspect sometimes that a pinhole in the brake booster could be the problem(your braking is a constant when rolling to a stop). I do need to check the throttle plate clearance as well, I set the CTPS by eye with the TB off the car and I don't really see it varying by more than a couple thousandths from what its supposed to be. But it could be a slight deviation in the vacuum at idle too small to see on the gauge.

In my case I think it's being aggravated a clogged fuel pickup screen and old injectors. All of which will be ruled out as soon as I get the remaining parts (Supra pump, AFPR) to install my Evo 560cc injectors and 2G MAS. I will be purchasing a chip from Jeff at the same time. Fuel starvation or a poor spray pattern might explain the idle drop. There is a tad bit of unsteadyness if I accelerate slowly through the RPM range.

I will say that it is way less aggravating than it was prior to the TB change FIAV blockoff. In my case I still have a few too many variable to eliminate before I can totally solve it. The biggest being the fuel/injectors.
 

Quote:
it takes four or five seconds or more to drop down to a nice steady 850 RPM.



I've ALWAYS had issues with my FAIV being hyperactive. It compensates TOO MUCH when the weather turns cold, giving me a high idle, so I blocked it off. Does turning the BISS in 1 turn fix the problem? If so, then I would suspect the FAIV. Just remember to turn the BISS back out when the weather gets warmer.
 

Thanks, Jeff. I will give it a try.

BTW...running 16 lbs boost on the new chip with the 3g intake and the 8.5:1 timing maps...minimal knock in third at the top. Car runs great.
 
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