Firebird RPM while idling

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darkeddie - 25 Jun 2006 04:45 GMT

What is the recommended/best RPM when the car is idling or in park? I
got a 1994 Pontiac Firebird (3.4 V6, automatic) and after I had my AC
recharged, it's idling at around 1500 RPM, it used to idle at about 800
RPM. The mechanic said that the "computer is re-learning how to handle
the AC and that I need to drive the car for a few miles". Is he right?
How many miles is "a few miles". Is the car in any danger?

I also had one of the hoses (the one that goes from the right side of
the radiator, near where the air filter is, to wherever) replaced
because it had a leak. Is it possible that the problem lies there?

(sorry for the cross-posting, I value the usenet groups and I want to
peek as many brains as possible).

Thanks in advance.

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Mike Hunter - 25 Jun 2006 21:21 GMT

He is not correct. In the days before computer controlled engines, the idle
needed to be set a bit higher to allow for generator/alternator load. When
the AC was turned on the idle speed was increased to take care of its extra
load. Today the micro processor adjust the fuel/air ratio to take care of
the additional load, or the removal of load, and the idle speed does not
change.. The idle therefore need only be around 700/800 RPMs

mike hunt

> What is the recommended/best RPM when the car is idling or in park? I
> got a 1994 Pontiac Firebird (3.4 V6, automatic) and after I had my AC
[quoted text clipped - 11 lines]
>
> Thanks in advance.

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Garrett Fulton - 26 Jun 2006 01:32 GMT

> He is not correct. In the days before computer controlled engines, the
> idle needed to be set a bit higher to allow for generator/alternator load.
[quoted text clipped - 20 lines]
>>
>> Thanks in advance.

That's wrong on every computer controlled fuel injection car I've ever
worked on. The computer controls idle speed by bypassing air around the
throttle plate to increase or decrease idle speed as a function of load.
The O2 sensor input to the ECM goes slightly lean due to the increase of air
from the idle air control circuit, and correspondingly increases injector
pulse with slightly. Or decreases pulse width when the load is removed and
the IAC circuit provides less air. That is an accurate representation of
the operation. You can see this happen with a Genesys scanner very easily.

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Mike Hunter - 26 Jun 2006 15:15 GMT

What part of; 'Today the micro processor adjust the fuel/air ratio to take
care of the additional load, or the removal of load,' did you not
underatnd? ;)

mike hunt

>> He is not correct. In the days before computer controlled engines, the
>> idle needed to be set a bit higher to allow for generator/alternator
[quoted text clipped - 31 lines]
> representation of the operation. You can see this happen with a Genesys
> scanner very easily.

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