random engine revs,wierd idle

[240sx1234]

looked at the search,but nothing i see to really answer my question
i have a 95 240sx se (stock ka24de) and hks exhaust only things ive done to the car,when the car is just sitting by itself it will randomly start to rev up and down.not to high like maybe 1500 at most then back down,it does it when i turn the wheel and turn the heat on which draws more power...i know.but sometimes it will just do it sitting there without touching it.if you need any more info to help me fix my problem let me know.it just feels like the rpms go so low and vibrates a lil and feels like its about to stall (5 spd btw)

[Pirate_Freder]

idle air control valve(IACV), throttle position sensor(TPS), and mass air flow sensor(MAF or MAFS) are where I would start. If you don't already have an FSM you need one(free download link below), you can also buy a Chiltons at an auto parts store if you choose, they are pretty good but DO NOT get a Haines, Chiltons or Nissan FSM only.

turning the heat on raises the rpm's though? that's odd...you're sure you don't mean when you turn the a/c on? that and turning the wheel are normal, should raise a couple hundred rpm's at those times(if idling).

Does it always do this or does it correspond with cold or warmed up? random? any connections at all?

Manuals > USDM Cars > 1991-1994 240SX (KA24DE) - Nissan 240SX Performance Tuning

[rocksteady_racer]

Just throwing this out there - if you have a an aftermarket stereo like I have a 600Watt amp with 1.2 Farad capacitor and at idle it'll jump up and down to charge with the alternator even with the cap.

But if you don't then...
My s13 ka24de has a valve cover leak at the top where the hose is connected (somehow the stock metal tube came loose) so that's been causing a very minute vacuum leak creating an erratic idle. So i'd check to see if the valve cover is leaking or there's a vacuum leak anywhere. Or my second guess if not vacuum leak (possible also from the iacv) is the tps sensor is going bad (just check it with a multimeter to see if it's still in spec). For example. My ka24e's tps sensor polarity somehow reversed on it's own which confused the ecu into an erratic idle. I'd check those two things first since they are the easiest. Last if neither of those fix it then i'd clean out your iacv thoroughly - there's a thread around here somewhere that show's you how to do it - remove, dissamble, thoroughly clean and then reinstall.

Hope that helps you out.

[rocksteady_racer]

O and if it's doing it when you turn the heat on - mostly like it's a vacuum leak because that's when my ka24de's idle is most erratic. Just my 2 cents. With the heat on it jumps from 550 to 1100 - with it off it'll hover around 700-850

[Hashiriya415]

If your o2 sens is 1 wire. Make sure your exhaust still has the ground strap on it. Somebody doing an exhaust and not paying attention to the ground could have easily left it off.

[swayray]

the sensor on the high pressure steering line maybe the cause of the weird idling when you move you steering wheel.