IAC at startup

[bad V6]

Should the IAC counts be at 175 upon startup, with the car being cold, then begin to settle into the desired range? The IAC motor is a new GM, installed last fall and set according to the GM Service Manual.

When I started the car over the weekend, after setting for a period of time, the IAC was at 175 and the car idling at 1800 RPM. Shut car off then restarted, IAC went to 85 and idle at approx 1200 RPM. As the operating temperature rose the car settled to a more desirable idle speed and sensor readings. Is this normal?

Direct Scan readings after car had warmed up (closed loop):

Speed 0mph
RPM 842rpm
TPS 0.46V
LV8 27
MAF 5g/s (taken from Gen 2)
IAC 22
Inj PW 1.75ms
Battery 14.4V
Coolant 157F
MAT 62F
Spark Adv 25.0
A/f Ratio 14.8
O2 volts 533mV
INT 128
BLM 128

Does anything look out of line? Or am I just paranoid about the fast idle?

Thanks,
Pat

 

[johnnyttype]

i have heard of this before, i think it is the computer losing track of the IAC motor position. i think it happens sometimes when changing chips, also i guess a killswitch that cuts power to computer would do it too if u have one. the only think out of ur numbers i see is to lower the TPS to .42 or lower. hth

 

[Sleeper-6]

I'm not sure about the cold start IAC, I've wondered this myself. I have noticed my car doing the same thing after an ECM reset or abnormal shut down. (stall, load up, ect) But your closed loop numbers look great, As long as it settles down to normal I wouldn't worrey about it too much.

 

[TurboDave]

Cold start IAC should go quite high (this will be different with every car), to get the engine on high idle (sometimes as high as 2000) depending on the car, and will start coming down, as it reduces the rpm down towards a more normal idle rpm.

 

[mikestertwo]

A lot depends on the chip you are using and where it sets the IAC count vs temp.

 

[TurboMonte 2]

You 1st need to get TPS adjusted to .44 max--over that & it can screw things up. Shoot for .42 & IAC of 15-40--warm,,,

High, cold rpm of 1500-2000 is abnormal w/ each start--assuming you have not cut power to ECM between starts,,,

What chip are you running??--did not see in your siggy... I've had several TTwk chips & a Red Armstrong & none of them routinely did this (only if I had previously disconn battery or otherwise cut power to ECM...

 

[TurboDave]

High, cold rpm of 1500-2000 is abnormal w/ each start...

On a warm restart yes, abnormal. On a cold restart, no not abnormal.

 

[bad V6]

I am running an Extender Extreme chip from Full Throttle.

I just ventured back into the garage and started the car, been setting since this past Friday. IAC went to 150 and idle around 1200 RPM, settled down to an IAC of 22 and idle at 850 in a little over a minute.

The TPS checked .42 and 4.74 with the ignition on/engine off. Do I need to lower the TPS?

Thanks for the input. This is my first turbo Buick, and previously was only around a '79 Buick LeSabre 3.8 turbo (dad bought new when I was a kid), I can still remember begging him to get on it. The thrill of the turbo boost captured my attention at an early age.

 

[TurboDave]

I am running an Extender Extreme chip from Full Throttle.

I just ventured back into the garage and started the car, been setting since this past Friday. IAC went to 150 and idle around 1200 RPM, settled down to an IAC of 22 and idle at 850 in a little over a minute.

The TPS checked .42 and 4.74 with the ignition on/engine off. Do I need to lower the TPS?

Nope, it's perfect.

Thanks for the input. This is my first turbo Buick, and previously was only around a '79 Buick LeSabre 3.8 turbo (dad bought new when I was a kid), I can still remember begging him to get on it. The thrill of the turbo boost captured my attention at an early age.

 

[bad V6]

Thanks Dave.

Now if this crazy weather would just straighten out.

 

[TurboMonte 2]

Like Dave said, you're just fine w/ these #'s & don't need to adjust anything. Just drive & enjoy it--hope your weather breaks for you soon. Golfed the last 2 days here!

 

[bad V6]

Thanks for helping me to have a better understanding of what to look for and why.

Upper 40's at daybreak, light rain from daybreak until mid morning, wind picked up, and now it's snowing. Seems like we're stuck in this cycle temps warm up, a couple of days later it rains and turns colder, then starts all over again. The weather has either been bad or temps to cold to get the car out much, I've only had it out twice so far this year. It's bound to break soon. Well atleast the track reopens March 1. That's something to look forward to.

 

[dennisL]

QUICK6 - The ECM program that controls the IAC is fixed in ROM but all the parameters or variables are in the PROM chip. This means they might be changed by the chip maker.

Here's what the stock chip (or stock IAC settings in a modified chip) do. The ECM causes the IAC to "park" at 150 when you shut down the engine so this it where it is at the next start up. As soon as the ECM determines the engine is running (400 rpm min), it reads the next IAC position from a table. This table has an IAC count for each of 9 coolant temps. The stock numbers are 150 for 90 degreesF and coolder. Most chip tuners reduce this for 90 deg and some do it also for 46 degrees. I don't have an Extender Extreme chip so I can't tell you what numbers it has.

The ECM doesn't even look at rpm for another 8/10ths of a sec, then it uses another table that provides a target rpm based on coolant temperature. It now adjusts the IAC to meet or get close to the target rpm. Again, these numbers can be changed but the stock rpm for a cold engine (68 degF and below) range from 1250 to 1400 rpm in Park. Most custom chips reduce this slightly but not much.