How much does your idle drop when you turn on heater?

[surreybc]

for a 1991-1994 240sx

I'm asking you to note how much your idle drops when you turn on interior heater. Mine drips 100 rpm. And remains dropped. I have had two alternators in my car recently and my idle dropped 100 rpm for both.

[blackrms13]

turning on heater as in push it all the way to hot and a/c button on, and fan on?

[surreybc]

turning on heater as in push it all the way to hot and a/c button on, and fan on?

a/c off. interior heater on hot ie fan on at highest speed. I just want to know if it is normal for the idle to fall when heater is on or headlights are on when a/c is off.

[rb25crazy]

my idle usually goes from 800rpm to 1000rpm actually increases hehe. sometimes it just stays at 800 rpms.

s14 btw

[BoostedCoupe]

Mine drops about 200 in my s13. If your idle is dropping to much just push the ac button, it will make the car idle higher but you will still have heat.

[slothonaleash]

My idle drops for about a half second then comes back up to normal.

And my s13's a piece of shit.

[ixfxi]

get a voltage gauge. idle drop means nothing.

also, i dont use ac with the heater function unless its high humidity

[soldiaboy]

no need for that shit down here

[surreybc]

thanks for the responses. Keep them coming.



I'm pretty sure the computer tries to maintain a certain idle. I'm not sure what determines that idle. Some people say it goes by how far the idle screw is turned in but that makes no sense since there is no sensor etc there for computer to monitor.

Im guessing the computer tries to increase the idle using the aac valve?

[surreybc]

The FSM says that the computer learns from experience what is the lowest idle needed to keep engine running smooth. It then records this to memory and uses it as a target. My idle is around 1000 rpm so I assume when my idle drops to 900 rpm this is still above the target idle so the ecu does not respond. The IACV is probably never used except when I have a sudden deceleration because my idle is always way above the target idle.
ECU uses crank angle sensor to measure idle rpm's.

[kevmeistah21]

mine drops about 200 rpms for like 30 seconds.

[handinpants]

I idle at about 900-1000, when I put the heater on the idle does not drop, when I put the AC on, the idle drops to 600 -750, I have an s13 with sr20det

[surreybc]

I idle at about 900-1000, when I put the heater on the idle does not drop, when I put the AC on, the idle drops to 600 -750, I have an s13 with sr20det


If your engine is anything like the ka24de, your idle should increase 300 rpm when A/C is turned on. the ficd on the iacv is there for that reason.