Hmm. . . Is this normal?

[Jagstang]

Hello everyone, I seem to have a weird problem when my vehicle is idling. . .

Basically, if I ever turn the heater on (while the car is in idle), the RPM's goes from 800 to 1100, then it drops down to 800, then bumps back up to 1100, and it continues this annoying cycle until I shut off the heater fan (which in turn causes it to return to 800).

It just annoys me because it makes so much noise, and it's so loud (due to the fact that I'm supporting a 3" cat-back exhaust and a test pipe). . .

Anyways, is this normal, or not?. .

Help would be greatly appreciated, thanks in advance.

[numbnuts240]

my idle will go up if i turn on just the windshield de-fogger, but it won't fluctuate like that. it definitely isn't normal.

[sr20power]

^ i agree. It may go up and but should settle back down to 800 rpms when you use/turn on some accessories. Yeah it is not normal to be bouncing up and down.

[Jagstang]

my idle will go up if i turn on just the windshield de-fogger, but it won't fluctuate like that. it definitely isn't normal.

Yeah, it happens when I turn on the windshield de-fogger (cause that's all I use). I haven't tested the other fan settings, but i'm sure it probably does the same thing?
Modified by Jagstang at 11:26 AM 12/15/2009

[bersh240]

ah. crap.mine does this too.here i thought i knew all the problems my car has.

[simmode1]

My s13 does this when it's cold, but once it reaches normal operating temperature, it settles down to normal...

[blacksrjdm]

Sounds like either all of you have air in the systems, or, you are seeing the rpms go up slightly from the A/C comp turning on with the defrosters.

[bersh240]

i doubt all of us have a/cmines longg gone

[Jagstang]

Sounds like either all of you have air in the systems, or, you are seeing the rpms go up slightly from the A/C comp turning on with the defrosters.

Oh s***. . . I DO have Air conditioning. . . Is that why? It just doesn't seem normal why the engine's RPM's always jump from 800-1100 all the time (while the de-fogger is on). Only when I shut off the de-fogger, my RPM's stays at 800.
Modified by Jagstang at 12:12 PM 12/15/2009

[greencar]

yes when you defrost, it kicks in the A/C compressor, and basically runs the A/C. air from the blower motor is blown over the evaporator to prevent the fogging of your windows

-Dan

[Jagstang]

yes when you defrost, it kicks in the A/C compressor, and basically runs the A/C. air from the blower motor is blown over the evaporator to prevent the fogging of your windows

-Dan

Alright thanks a lot. But is my RPM's bouncing range too extreme? As you've mentioned, the A/C compressor kicks in, causing the RPM's to increase and decrease, but by 300 rpm's? That seems like a tad too much doesn't it?

[greencar]

seems normal. mine goes to 1200, but i dont have the ac belt on currently. so it doesnt have a load.

-Dan

[Jagstang]

seems normal. mine goes to 1200, but i dont have the ac belt on currently. so it doesnt have a load.

-Dan

Alright thanks a lot for the response. Hmm I should have known, 240sx abnormalities are the OEM stock normality. . .

[numbnuts240]

it's normal for the rpms to go up. what's not normal is that your idle is constantly fluctuating. it should stay up in the 1k-1200 range, not drop back down to 800, then back up to 1k-ish, etc.

[blacksrjdm]

Ya, that isnt normal at all. I would first make sure to bleed the coolant system properly to be sure there is no air. If you are successful there and there is still an issue, then check all your vacuum lines.

If you try to hold the throttle at 1000 rpms without the heat or defroster on what happens? Will the throttle stay at 1000 or fluctuate?

[SirSilvia]

I thought this was normal so i never buggered with it. I thought the engine was just compensating for the load of the accessories and the stat opening/closing to cool the engine more. Never thought it could be air in the system, its been like this for the 5 years i've owned it.

[FolkertSX]

hey guys i got a question too. a month or so ago i started my car and it was idling real real rough. after 5 min of running it got less worse, then driving it got horrible again and i had no power like at all. now eveyrtime i start my car it will idle fine, ill put in into first, start to drop the clutch and it will die, still dies even if i put the clutch back in, so then i restart and it runs perfect everytime. anyone know why this could be?