Rpm When I Start Ac In Engine Idle

[Ted]

Hi guys,

I was told by someone that engine rpm should go slightly 1000 up and come down, when I start the AC in car engine idle state. My car AC does not give that nature.. After i keep some time to get the engine idle to an rpm of around 600, and when i start AC on, then rpm only goes up around 700 not upto 1000. Is this an unusual condition?

P.S. I was focused on this because I have a lil bit sound and a lil vibration when AC is on. ( also my ac fan belt has tiny cracks inside going to replace it but rpm problem is not caused by it i think.) Appreciate if somebody could comment on this..

Also the car was stopped suddenly when AC is on and in idle state. It has happened 3 times. Going to hv an engine scan as well.

My car is a 260 premio

[Rumesh88]

When was the last time you got your engine tuned up (I mean a throttle body clean up done)? Does your engine rev up to around 1500 RPM when you start when engine is cold and then come down to 600 after a few minutes?

[Davy]

To answer your first question, the normal behaviour is that there is little to no change in RPM when the AC comes on. The idle control mechanism should stabilise the engine RPM as the compressor comes on and goes off. So no, it shouldn't rise to 1000 and come back down every time the AC comes on.

[Ted]

Hi Rumesh, i did last tune up when my milage was 48k. Now milage is 60k. Also when cold strt rpm sudden goes to around 2k and then comes down to 700 smthing.

When was the last time you got your engine tuned up (I mean a throttle body clean up done)? Does your engine rev up to around 1500 RPM when you start when engine is cold and then come down to 600 after a few minutes?

[Rumesh88]

Hi Rumesh, i did last tune up when my milage was 48k. Now milage is 60k. Also when cold strt rpm sudden goes to around 2k and then comes down to 700 smthing.

A scan is unlikely to give you a clue although a fault code can be found stored in ECU. Any idea if the injector washers were changed and PCV valve cleaned when it was tuned up? Injector washers tend to develop tiny cracks over time and give trouble at idle. In addition to those above, stability of the idle RPM depends on many other factors as well. It can be due to a vacuum leak at the intake manifold, bad spark plugs, bad ignition coil, erratic fuel delivery of injectors, MAF sensor, TPS sensor, a slight compression leak in a cylinder etc etc... but take care of the simple things like spark plugs, vacuum leaks, TPS (which can be tested) and PCV first. What's the sound you say at idle like?

Edited June 21, 2016 by Rumesh88

[gayanath]

Hi guys,

I was told by someone that engine rpm should go slightly 1000 up and come down, when I start the AC in car engine idle state. My car AC does not give that nature.. After i keep some time to get the engine idle to an rpm of around 600, and when i start AC on, then rpm only goes up around 700 not upto 1000. Is this an unusual condition?

Is this the normal behavior of your car since you purchased, or do you feel this is a resent change?

P.S. I was focused on this because I have a lil bit sound and a lil vibration when AC is on.

Is this vibration a normal behavior of your car since you purchased, or do you feel this is a resent change?

Also the car was stopped suddenly when AC is on and in idle state. It has happened 3 times. Going to hv an engine scan as well.

This three times are withing one or two days or withing long duration?

My car is a 260 premio

Hi Rumesh, i did last tune up when my milage was 48k. Now milage is 60k. Also when cold strt rpm sudden goes to around 2k and then comes down to 700 smthing.

YOM?

Millage when you purchased?

Did you replaced your battery?

If battery replaced, when it replaced?

Why you did a tuneup at 48K? Due to any issue?