Air conditioning is pulling down idle

TomCat · 14 September 2014

My idle rpm is solid/perfect (~800) but when I turn on the a/c it drops without the "bump" I would expect from the "computer" down to ~300rpms.
I checked the electrical plugs on the IACV...nothing obviously wrong.
Thanks

jaja · 14 September 2014

Any CEL?

TomCat · 14 September 2014

Funny, I have a CEL since CTSC install but no codes (ODBI, 1991) and the car runs perfectly.
My 300ZX TT has a circuit that kicks up the idle when ac is on, I assumed it was comon/standard in most of these cars.

RYU · 14 September 2014

A lot of load on the electrical system (AC compressor clutch, AC blower(s)) coupled with a lower than stock output alternator... See if it gets worse with all the lights on. It should.

check your voltage. might want to check the health of your battery.

TomCat · 15 September 2014

Thanks...is there a idle "bump" circuit to compensate for the a/c?

Briank · 15 September 2014

The idle speed is controlled by the computer (ECU) using the IACV valve. If the system can not compensate for the increased load of the ac then the first thing to do would be a throttle body cleaning.

Larry Bastanza · 15 September 2014

In regard to Brian's comment about the IACV does the car fast idle properly when it is cold? The answer to this quesion will help isolate if it is a potential clog in the IACV system, or actually some type of electrical fault.

RYU · 15 September 2014

Larry Bastanza said:
In regard to Brian's comment about the IACV does the car fast idle properly when it is cold? This will help isolate if it is a potential clog in the IACV system, or actually some type of electrical fault.

Larry, this is off topic but I just wanted to thank you personally for all your advice here on prime. I had a CEL code 42 & 43 (I think those were them) and was scratching my head as to what it was. An old post from you pointed to a cross-wired set of O2 sensor wires. Thanks again, that was exactly it.

TomCat · 15 September 2014

Larry Bastanza said:
In regard to Brian's comment about the IACV does the car fast idle properly when it is cold? The answer to this quesion will help isolate if it is a potential clog in the IACV system, or actually some type of electrical fault.

Idles faster when cold then settles down nicely when warm...
No hunting idle, etc...

BrianB · 15 September 2014

I've got a similar issue and found it to be voltage related. I have the new CTSC on a auto. And when the a/c comes on the idle slows as well. But they tuned some of it out. And found that my new denso alternator is only putting out 11.5-11.9 volts at idle so when I have the AC on and click to reverse or drive it sometimes turns off on low voltage. I've tried to get ahold of a warranty alternator but haven't herd back yet.

Check your output on your alternator with a good multimeter read right at the alternator. Or have someone watch it. As you turn the A/C on and off. Maybe it's the same issue.

BATMANs · 15 September 2014

It's a MPG saving feature that a select few NSXs were gifted. Namely those made on a Weds.

nigel · 16 September 2014

A/c

Per Brian / Larry now me, IACV.
Remember, "don't replace the crankshaft if it only needs an air filter".

Cheers
nigel

TomCat · 16 September 2014

BrianB said:
I've got a similar issue and found it to be voltage related. I have the new CTSC on a auto. And when the a/c comes on the idle slows as well. But they tuned some of it out. And found that my new denso alternator is only putting out 11.5-11.9 volts at idle so when I have the AC on and click to reverse or drive it sometimes turns off on low voltage. I've tried to get ahold of a warranty alternator but haven't herd back yet.

Check your output on your alternator with a good multimeter read right at the alternator. Or have someone watch it. As you turn the A/C on and off. Maybe it's the same issue.

I'll check the alternator output.

Air conditioning is pulling down idle

Similar threads