About to buy MS3 question about IDLE HELP plz

[5][Spyder]

Seriously considering buying an MS3, all the paperwork is good, but I noticed when idle in neutral with the A/C on it would vary the idle in a cycling manner - (idle at X rpm, increase for a second or 2 by 100rpm maybe or less, go back to X rpm, but in a perfectly timed cycle) turning off the A/C the idle is 100% steady....is this normal?

 

[staples187]

Seriously considering buying an MS3, all the paperwork is good, but I noticed when idle in neutral with the A/C on it would vary the idle in a cycling manner - (idle at X rpm, increase for a second or 2 by 100rpm maybe or less, go back to X rpm, but in a perfectly timed cycle) turning off the A/C the idle is 100% steady....is this normal?

On a lot of cars when you have the A/C off the car may run 750 rpms, but when the A/C is on it will run 850rpms, yes that is normal. Also you may notice in neutral if you turn the wheel the rpms may go up. As long as the car isn't rough idling you're fine.

 

[5][Spyder]

nono I understand that cars will adjust idle for having the A/C on or bog down the idle while turning the wheels(load on the power steering pump) thats normal. What I'm talking about is a varying idle, for example:
Ac off:
750
750
750
750
750
750
750
750
AC ON:
750
750
750
850
850
850
750
750
750
850
850
850
750
750
750
same cycle over a 5 minute period, never getting better or worse
AC off:
750
750
750
750
750
750
750

perfect cycle.
those aren't accurate numbers, just an example.

The reason I ask is this is an amazing deal on the car, but it has 300 miles on, so it could have been abused in that time, you know how this s*** goes =(

 

[Sacrilicious]

sounds to me like that's very normal. the AC compressor isn't on 100% of the time when the AC light is on, btw. that is why you're getting the cycling thing. try this: set the temp really really low in the car...see if the cycling becomes more frequent. if so, that's confirmation that it's the compressor kickin in. it is very normal for the compressor to do that to you idle, because compressors draw a lot of current, so it's gonna really push your alternator if you're idling.

 

[5][Spyder]

thanks for the response, but I'm pretty sure compressors don't draw power at all, they run off the engine belt(physical energy) and the blower motor should be the only thing in the AC system that is loading down the alternator.

But its very likely like you say, that maybe the AC comp. is only having to cycle on and off to keep that temperature range. I can't do any testing b/c I 'm back at home now, and thinking over the purchase.

I would REALLY appreciate it if someone could go out to their car on a 60' deg area of the world, idle with it warmed up with the AC on in neutral and tell me what their does, would REALLY ease my mind about buying the car, (kissass)(kissass)(kissass)(kissass)

 

[Rotus8]

The compressor takes a significant amount of power from the engine drive belt. It has a clutch on the compressor that kicks it on and off as needed. The ECU ups the RPM to keep the engine from bogging. Perfectly normal.