Idle fluctuation when i'm idling on idle.

[95zilvia]

When my car's warm, and I'm in neutral... sometimes the idle will jump up to 1500, then drop to 500-800, go up to 1500, then drop to 500-800. It'll keep doing this.

I think it could be several things-
Coolant temp sensor
Vacuum leak
Idle Air Control Valve
Atmospheric BOV???

Anyone can help me narrow it down?

Oh yeah, it's an S13 redtop.

[S14DB]

I would say coolant temp sensor. They tend to give wild swings when they go.

[nacstate]

Mine does that when the fan kicks on, but I thought that was normal.

not so normal??

[kingsol]

did you check your injectors? my idle did the same thing before i found out i needed to replace an o-ring.

[omen2853]

clean your AIV valve or just plain remove it. if that doesnt work, check for vacuum leaks, and go for the rest of those things you listed. first though, id check the AIV

[95zilvia]

So basically, everything is broken, haha.

[Dream240]

Mine does that when the fan kicks on, but I thought that was normal.

not so normal??

It is normal for the idle to fluctuate when the cooling fans come on, same goes for when you turn on the A/C. But the revs should level off after a couple seconds.

[nacstate]

It is normal for the idle to fluctuate when the cooling fans come on, same goes for when you turn on the A/C. But the revs should level off after a couple seconds.

ok thats what I thought, i'm good.

[aznpoopy]

i had the same problem.

massive oil leak from front main seal was gunking up my alternator. cleaned it off and resealed.

also, cleaning the electrical grounds in the engine bay seems to have helped alot too.

jumping up to 1500 is normal; but i don't think it should take a bit for it to level off at regular idle. mine goes up to 1500 and right back to 800rpms.