Z06_BluByU

i'm tring to track down a driveability issue.. runs rich, idles like crap-o-la.. I have a custom chip for my modifications.. i'm thinking its the IAC gone bad..

At cold idle i'm getting 130-152 IAC pos (counts) that seems high! at warm idle it reads 76 at startup and fluctuates to 96 or so in open loop.. once in closed loop it goes down to 52 counts?!? does that sounds like something is wrong?

the TPS reads .65 volts at 0% TPS opening.. and 3.49 volts at 98% opening..


at idle i'm pulling around 17 Hg of manifold vaccum according to my MAP sensor..

the driver side 02 reading reads 0 volts for a 7th of a sec. sometimes (one record of data) while driving around.. once in a great while..

I also noticed at 5500rpm @ WOT my calc. injector Duty cycle is at 99%

fuel pressure checks out.. both with engine off/key on and car at idle..




[Modified by BluByU, 6:05 AM 10/30/2003]

AGENT 86

I would rule out IAC as the source of your problems. It's only purpose is controling idle speed. Your wot TPS voltage seems a little low. Is the EGR functioning normal ? :cheers:

Z06_BluByU

it idles like crap and almost stalls out at first startup.. then it kinda recovers after a few seconds.. also idle is hit or miss.. sometimes it idles pretty good.. turn it off go in a store come back out turn it on and bamo instant crapo-la-idle..

i physically inspected the EGR and it moves freely.. the ECM is showing it is duty cycle moving from time to time.. usually with the CCP DC..

the motor is a 383 with this cam.. COMP extreme CCA-218-224-12

@ .50 - intake duration 218 exhuast duration 224 intake lift .495 exhaust lift .503 LSA 112

everything else is stock except the computer chip.. which was done by PCMforless.com

does the IAC ever need adjustment?


[Modified by BluByU, 6:49 AM 10/30/2003]

AGENT 86

The IAC is self adjusting. Are your idle speeds very low ?
The only time you would adjust your IAC is when your installing it.
Have you looked for all possible vacuum leaks?

Z06_BluByU

idle is very low..
i took the IAC out to clean it.
i dont hear any vaccum leaks.. would an exhaust leak before the 02 sensor cause a problem?

Z06_BluByU

I read in the archives of people opening the throttle blades more.. however, should the air bypass hole be enlarged since the displacment of the engine increased (383)? I guess thats the same as opening up the throttle blades more..

JAKE

No, no enlarging of the by-pass hole is called for.

Okay, just went through this over the past several days when I installed a new 52mm BBK TB.

Stock, IAC counts should be 20 to 25, but you can throw that out the window when you mod the engine.

My engine was doing much the same thing, so I began adjusting the TB minimum air flow setting to find the sweet spot.

You're engine is being commanded to idle at a certain RPM, the IAC will retract and extend in an attempt to maintain that RPM.

Problem was, for me, that if I had counts as high as yours, driving the car was a problem. I began by opening the butterflies using the adjustment screw, and I went too far, causing the engine not drop down in RPM when I was on the road and took my foot off the accelerator pedal.

So I kept playing with adjusting the minimum airflow setting until I found what it liked and what gave me the results I wanted.

I ended up with closed loop idle counts of 59, which is more than twice what the "books" call for. At 20 to 25 counts I had the problem of the engine starting with a roar and idle RPM couldn't be controlled effectively by the IAC.

So try opening the TB minimum airflow setting a bit at a time until you find what the engine, and you, like. After you get the minimum airflow setting right, the IAC will reset itself and all should be fine.

I'm assuming, of course, there are no vacuum leaks.

Hope this helps.

Jake

JAKE

I forgot to mention, after getting theTB adjustment you like, be sure to readjust the TPS voltage and the trans cable, if you have an auto trans.

The TPS voltage will definitely change; the trans cable, maybe, maybe not.

Jake


[Modified by JAKE, 1:31 PM 10/30/2003]

Darkness

That injector duty cycle is alarming, what size injectors do you have? Hope its not stock with that 383! You should never go over 90% on injectors. Check that out too, as for the idle, sometimes cleaning the IAC with brake cleaner is all that it takes.

Aaron's 87

You'll have to open up the throttle. Getting the idle right with your modded motor means balancing throttle opening, commanded idle, and timing among other things. What is your commanded idle and idle timing?

Z06_BluByU

commanded idle cold is 750.. warm 550.. idle timing cold fluctuates between 25* and 28*... warm between 16-20*


i opened the throttle blades a bit and it smoothed things out.. i et the IAS counts to 20 and it seemed to like it..

however, this morning i noticed the idle counts around 112 or so.. it was muggy last night and cool this morning.. i'll continue to refine it a bit.

Aaron's 87

Probably need more commanded idle and maybe need more idle timing. It's hard to tune over the internet. BTW, I shoot for 0-1 IAC warm with no accesories.

BLACKVETTE95

Jake,

When I installed my BBK, the only thing that was out of whack was the throotle cable position. When I bent the bracket and adjusted the throtle opening everything else worked right. On my 95, there really is no way to adjust the TPS other than drilling the hole larger.
Is that what you did?

Since everything worked right off the bat, I didn't even check the IAC or TPS.
Now I am wondering..... hmmm.

I do however know that with my hotcam set up, it likes to idle at around 900 rather than 750.



[Modified by BLACKVETTE95, 10:35 AM 10/31/2003]