Idling hiccup

[msvx95]

Something I've been noticing lately is that my idle tends to intermittently hiccup. Meaning it will idle about 650rpm, then dip lower to I'm guessing 400.
I see this problem while sitting at red lights or even while just idling in my garage. It will not do this all of the time, but sporatically. The temp gage is at normal.

Things to note: I have no codes shown, the car doesn't sputter, it drives great, and no loss of performance. MAF sensor (used but replaced 1-1/2 years ago)

What could cause a problem like this or is something starting to fail? I hope its as simple as a defective sensor....

[92 SVX]

Might be the idle air control valve? maybe it sticks once in a while?

[icingdeath88]

I have a similar issue, but I noticed that it happens when I come to a stop, rather than once I'm already stopped. My plan is to seafoam it, making sure to hit the aux air control valve, then check for vacuum leaks, etc. Maybe clean/swap out the MAF for one of the other two I have.

[msvx95]

I hope it's not the IAC valve..isn't that a b*tch to take out??

I checked my codes again...normal check engine blinks. I may check it with the car temp normal and driving it to work to see if the code blinks that way.

How much is a coil pack?...P/n, and where can I get a few in case I need them?

[SoCal LS-L]

Originally Posted by msvx95

Something I've been noticing lately is that my idle tends to intermittently hiccup. Meaning it will idle about 650rpm, then dip lower to I'm guessing 400.
I see this problem while sitting at red lights or even while just idling in my garage. It will not do this all of the time, but sporatically. The temp gage is at normal.

Things to note: I have no codes shown, the car doesn't sputter, it drives great, and no loss of performance. MAF sensor (used but replaced 1-1/2 years ago)

What could cause a problem like this or is something starting to fail? I hope its as simple as a defective sensor....

Am I the only one who thinks this might just be the fans kicking on and off?

[1986nate]

Each coil is around $80 from subaruparts.com or the site of your choice and probably not the issue here.

The coolant temp sensor can also cause a "surging" idle but usually only when the engine is cold. And no, it won't throw a CEL all of the time either.

[msvx95]

Originally Posted by SoCal LS-L

Am I the only one who thinks this might just be the fans kicking on and off?

I don't think the fans would just start acting up to do that in the past few weeks..if the fans kick on and off why would the rpm drop suddenly 200 rpm?

I drove today with my cel light blinking normally..so it's not picking anything up as an error, but maybe the coolant temp sensor is on the fritz?

I bought some fuel injector cleaner as well...may try that tomorrow.

[SoCal LS-L]

Originally Posted by msvx95

I don't think the fans would just start acting up to do that in the past few weeks..if the fans kick on and off why would the rpm drop suddenly 200 rpm?

I drove today with my cel light blinking normally..so it's not picking anything up as an error, but maybe the coolant temp sensor is on the fritz?

I bought some fuel injector cleaner as well...may try that tomorrow.

Because of the current draw lowing the system voltage momentarily, I notice a marked idle drop when mine come on.

[msvx95]

I notice when the car is idling and warming up, if the idle drops the parking lights dim briefly.