Chip & Idle Control

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Dec 6, 2005 | 02:25 PM

bigjack

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Chip & Idle Control

Am I correct in assuming that the chip is the basic controlling device regarding idle speed on an '85? Thanks

Dec 6, 2005 | 02:35 PM

CFI-EFI

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Basic? How about "only"?

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Dec 6, 2005 | 03:16 PM

Muffin

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From: Merritt Ils Fl

Quote:

Originally Posted by CFI-EFI

Basic? How about "only"?

RACE ON!!!

As always CFI-EFI is correct. You do,however set the base idle from which the ECM works.4

Dec 6, 2005 | 05:54 PM

bigjack

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Just Making Sure.....

Then, if the chip is incorrectly "burned" for a pre-determined idle rpm, no amount of other adjustment will allow for obtaining "that" rpm?

Dec 6, 2005 | 06:56 PM

CFI-EFI

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Quote:

Originally Posted by Muffin

As always CFI-EFI is correct. You do,however set the base idle from which the ECM works.4

Sorta, kinda, but not really. Unlike the ignition timing, there really is no "base idle". If you set your base ignition timing at the specified, 6° base, and the program in the ECM calls for 6° more advance, the car will have 12° advance. If you, now, set the base timing at 10° and the same conditions again call for the addition of 6° of timing, the ECM will add the 6° and have no way of knowing that the engine is experiencing a total of 16° advance. With the ignition, it is called "base timing" because any and all timing adjustments are made from the "base".

Adjusting the throttle stop screw doesn't set a "base idle". The purpose of that screw is to make the minimum air adjustment. Unlike with the ignition system, where the ECM doesn't know the timing, the ECM knows the engine rpms. The idle speed is burned into the prom, and the ECM will manipulate the IAC to achieve that idle speed, no matter what the minimum air or "base idle" is set at.

It would be possible adjust the minimum air to position the throttle blades so far open that the closed IAC couldn't reduce the idle, but given that the IAC has the ability to maintain a pretty healthy cold idle, that would be a very fast idle, indeed.

RACE ON!!!

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