Brief idle surge on '06 Forester when "cold"

[denversprings]

Hi all,

 

I'm new to the world of Subarus and don't know much about cars. I just bought an '06 Forester X, manual transmission. When "cold" (sitting for 3 or more hours), the car idles at about 1500 rpm at start-up. After I start moving and press the clutch in and let up on the accelerator (to shift out of reverse or from first to second), the engine surges to 3000 rpm. It does this for the first few shiftings and then settles down. After that, the engine idles at a nice 750 rpm. Air temperature doesn't matter--it does it whether it's 40 degrees or 70.

 

The mechanics at the shop checked into it and said that it's normal (something this sort of "IAC engine" does). Is this true? Anyone else experience this?

 

I'd appreciate any thoughts.

 

Thanks--denversprings

[mikem]

Congrats on your new sube. Hope you enjoy it. I have an 06 outback with the 3.0 engine and it is automatic but I don't see any large increase in idle rpm when started. Maybe a few hundred for a minute or so but nothing on the order of what you are seeing. However, rest assured you have come to one of the best places to get good information. I have certainly enjoyed my sube more by having been exposed to usmb. The collective talent and knowledge available here is incredible. Just hang on, somebody will know and will tell you. Welcome aboard!

[Jerry DeMoss]

When it does this jump in rpm at start up does it increase more with cooler weather? I was wondering if it does this on an 80 degree day or on a colder day around 30 degrees?Good luck.

[denversprings]

The jump appears the same, whether it's been sitting outside in 32 degree weather or in the sun on a 70 degree day. I can imagine a slightly faster idle on start-up, which it does (1500 rpm), but the jump to 3000 rpm in the middle of the first few shiftings seems strange to me. If I hold the clutch down and just sit there, it continues to idle at 3000 rpm for at least 5 seconds or longer before deciding to drop down to 1000-1500.

[wirelessenabled]

I have the same problem with my 2000 OBW MT w/ 80k miles.

 

Start it, idles nicely at 1500, back out of my garage without touching throttle, when I push the clutch back in it surges to between 2500-3200. If I shift in to neutral and let the clutch out it goes back to 1700 or so. Happens for about 30 seconds and then car is perfect.

 

No difference with A/C on/off, lights etc. Slightly worse in winter.

 

I have changed plugs from platinum to OEM Subie NGKs. New wires, new coil, new temp sender, removed and cleaned IAC, ran Seafoam through the TB. Checked all hoses for vacuum leaks. No codes set on OBDII.

 

Just living with it for now.

[TheBrian]

What you're describing sounds like normal operation to me. Until the vehicle is warmed up, reliable start-up and operation is a higher design priority than fuel economy.

 

It pays to be aware of this behavior when shifting, gassing, and clutching first thing on a cold day.

[Setright]

Sounds ok to me. My Impreza with a 2.0 liter engine will behave in the same way sometimes.

 

The mixture is rich because the engine is well below operating temp, and that mixture means high idle speed, and that the revs will drop more slowly. The ECU is trying to keep the engine from stalling.

 

If you feather the clutch up and leave the accelerator untouched when you reverse out of the drive, I bet it won't do this.

[wirelessenabled]

Sounds ok to me. My Impreza with a 2.0 liter engine will behave in the same way sometimes.

 

The mixture is rich because the engine is well below operating temp, and that mixture means high idle speed, and that the revs will drop more slowly. The ECU is trying to keep the engine from stalling.

 

If you feather the clutch up and leave the accelerator untouched when you reverse out of the drive, I bet it won't do this.

 

See my post above

 

"Start it, idles nicely at 1500, back out of my garage without touching throttle, when I push the clutch back in it surges to between 2500-3200."

 

No amount of feathering the clutch changes this behavior.

 

Book says idle should increase to 1500 while cold then go back to 750 when warm.

[blitz]

Software programming glitches are a part of the Subaru experience.

 

They really need to get someone on that tho. Too many benign but annoying behaviors of throttle, ABS, 4EAT, knock sensor, etc.

 

It's a pattern - not a good one either.

[Zefy]

from what i've seen, its normal... 01 legacy does the same thing...

 

i'm pretty sure its to warm up the engine and get those fluids flowing...

 

if you listen closely(at least on the 01) you can hear water entering the heater core after it warms a little... at least i think thats what it is... it sounds like water trickling...

 

so ya... its normal... not need to worry...

[cbons]

am having the same "problem" with my 92 Legacy, but it seems this is the answer. after cleaning the IAC inlet, is there a need to reset the computer settings?

 

the water trickle sound was getting me too, but now it makes sense.