Why is my car idling so high?!?


New Member
Mar 19, 2002
I just built a brand new LT1 motor for my camaro and have it controlled by Accel's 6.0 DFI and Calmap 6.32. Well with the idle on the Calmap set at 750, the car still idles at 1500! My idle air screw on the TB is set all the way in, so the blades are closed! My TPS reads 0% with the blades closed! I just can't get the car to idle down....does anyone have a few tips or suggestions I can try? I don't think I have a vacuum problem, but I will go check again later today. Any help would greatly be appreciated!
On a speed density motor (all motors really) idle speed is controlled by how much air
is getting into the motor.

Either thru the throttle blades:
make sure the throttle is really touching the stop screw
check for a throttle cable or cruise control cable that's too tight

Or the IAC
check the throttle follower screen or the VIEW screen for the IAC position

Or a vaccuum leak
check the PCV valve, heater control connections, brake booster connection, EGR.

I recall a friend getting a DFI that was "configured" wrong and it would not
control the idle speed. It had to go back to DFI to be fixed.... :(

They also had a reputation for blowing the IAC control chip...... :(

good luck.

I'm pretty sure there aren't any vacuum leaks, as I've checked and rechecked everything. On the throttle follower screen, the IAC sits at 1 when the TPS is at 0. On the stop screw thing, I have the stop screw in so far that the throttle arm isn't touching it anymore, The throttle is completely closed. Also another observation is today I went to start the car in the cold (35 degrees) and I had to hold the TB open a bit so the motor wouldn't shut off, but when it hit like 160 degrees (the motor) the idle jumped from about 800 to the usual 1500, even though I closed the throttle blades. Weird.

One more new thing I noticed, when the motor's up to temp (around 190-200 degrees) the O2 voltage jumps all around, it goes from 0.33v all the way to .88v and back and forth between those numbers. Why could that be?
A couple ideas,

1, the ECM is not controlling the IAC. if you have a
spare IAC, plug the harness into it and hold it in your hand and watch to
see if it moves.

My guess is: Bad IAC, bad wiring to the IAC, bad ECU. This assumes the desired
idle is really 800. (not sure how experienced you are)

O2 fluctuations, this is the nature of Closed Loop, the ECU is 'hunting' for 14.7:1
air/fuel ratio. This is normal.
Air has to be getting in there somehow, or the motor wouldn't run.

What happens if you put your finger over the IAC inlet while the engine is running?

-Bob Cunningham
When it is idling high, where does the "Throttle Follower" screen say the IAC is?
If I posted my DFI saved file, could you guys take a look at it and give me suggestions? Like if something in the programming looks to be off to cause a high idle? Here it is. It's a saved file from Calmap 6.32. 031102. The saved file is called 031102.dat. Thanks!
right below the throttle body there is a hole in the intake. Make sure there is a plug in that hole.
There's is a freeze plug already installed under the TB so it's not getting air from there at all. I replaced the IAC and the problem still persists. I KNOW that the air is getting into the motor through the IAC passage cuz when I put my finger over the hole the motor dies from lack of air. And the DFI is working the IAC valve, it's not dead. The IAC just seems to be working backwards for me. It's closed up at closed start, and when the motor warms up (after I hold the throttle blades open manually) the IAC opens up fully making the car idle really high with the throttle blades completely closed off. Is the problem within the program?
If you have the new style IAC (flat 4 wire Metri-Pack) you might want to check and make sure you have the wires in the correct holes. A high, A low, B high, & B low. I have seen some that have been backwards.
How do I know which pins on the IAC are A high A low B high and B low? I know which wires they are on the harness, but don't know which pins they're supposed to connect to exactly.
You might have to back probe you harness to verify that the wires are in their appropriate holes. On a DFI,

ECU Pin IAC Notes
C12 A A High
D13 C B High
D12 B A Low
C13 D B Low
I checked those pinouts and they were good on the back of the ECM and on the sensor side. I called Julio at Cartek (where I bought the DFI from) and he told me that only on LT1 applications, the IAC connections inside the ECM are backwards...so he told me to reverse the High A and Low A pins, and it worked! That's all that needed to be done. He says it's not the first time he saw it happen. Well my idle is now working according to the way it's set on the DFI and I feel relieved. I thank you all for your help and knowledge!