Eratic Idle With A/c On

LS Jasper · May 22, 2012

Hi,

First warm day in ages so gave the A/C a good cold blast. Working well but when I slow down the idle is erratic and takes an age to come down to the usual. Idle is fine with A/C off. Braking also feels a bit lumpy too. Any thoughts?

Jim

ambermarine · May 23, 2012

Hi,

First warm day in ages so gave the A/C a good cold blast. Working well but when I slow down the idle is erratic and takes an age to come down to the usual. Idle is fine with A/C off. Braking also feels a bit lumpy too. Any thoughts?

Jim

Hi Jim

The A/C uses more revs than idle it requires approx twice as much which will be around 1200/1350/rpm it will go up and down as the compressor clutch engages and disengages for different periods of time depending on how long it takes the temprature to adjust to your setting in the cabin.

When the car is in normal drive mode the change in engine revs will not be as noticable,as for the braking ,that could be the anything but would have nothing to do with the A/C.

steve2006 · May 23, 2012

When you say the brakes feel "lumpy" do you mean you need more pedal pressure to apply the brakes than you would normally?

The idle speed as already mentioned is increased slightly to allow for the load of the compressor on the engine so I would check all your vacuum pipes for secure connections and the IACV for possible sticking.

Low vacuum can effect both the idle speed and braking system.

LS Jasper · May 23, 2012

Thanks for the replies. Yes, more pedal pressure required than normal. How do I find out where all the vacuum pipes are!?

steve2006 · May 24, 2012

You don't say which year you have so you may have an engine cover fitted, if so remove it and check all the black pipes around the engine for splits or loose connections.

LS Jasper · May 25, 2012

Sorry, 1995. Will check under the cover this evening. Idle is perfect normally, just with the A/C that it is up and down like a yo yo! I have also seen some other threads on checking/cleaning the IACV. I run on LPG and assume that this should minimise the build up of carbon deposits on IACV? A mechanic mate told me than when he strips down an engine run on LPG it looks like new compared to petrol-run engines. Certainly the inside of my exhaust when I was under the rear bumper looking up into it has a lovely silver/gold sheen.