I wanted to see if there's anyone that has experienced a cracked intake manifold?  I've got a 2002 Outback with the 2.5 boxer.  176k miles.  

There's a long saga that got me to this point...  but...I replaced the MAP sensor...and looked down the hole...and saw a puddle of antifreeze.  

The engine is pretty happy at 2000 rpm and above...but won't idle and cuts out.  The RPMs will also oscillate wildly from 700 to 3000 rpm if I let her sit there and do her thing.  White smoke out the exhaust.

Can the coolant passages crack and pass coolant into the intake air passages?

I appreciate any ideas you all might have.

Thanks.

I think I read once of a casting flaw or crack in the throttle body that let coolant in.

 

and I think coolant is bad for O2 sensors so, maybe it's bad now too?

 

I'd think a coolant system pressure test would help locate the problem quickly.

automatic or 5 speed ?  The iac valve, idle air control sits just in front of the throttle body . It has coolant to it .  Not sure about the automatic in that year but it is different from MT,  on the 5 speed that housing could have cracked and be letting coolant into throttle body.  This could explain your poor or no idle issues.  Or your coolant could be leaking elsewhere and your idle is not related. Do a pressure test on the cooling system and see if its leaking down. The iac valves are known to have issues in that year group, I just cleaned mine (2000 obw), it was going up to 2000-3000 rpm on startup & would not idle down until the engine was fully warmed up.   Replacement valve for the auto was $30 the MT replacement was around $150... SO   I removed and cleaned mine ...   After cleaning it did not high idle anymore but seemed like it was lower than normal for a cold start. Then it started dying at idle ... start right back up ... run a few then die  again. Down the road it ran great.  After a day of poor idle (still low ) it cleared itself up and now it is 1500 on cold start , quickly drops to 1200 then down to 800 where it will sit all day. I used carb clean and rubbing alcohol with Q-tips to clean it up.  

check, clean, replace the IAC gasket, it has a coolant passage associated with it:

 

http://s9.photobucket.com/user/scooterforever/media/IACVGasketOld.jpg.html

 

 

...and looked down the hole...and saw a puddle of antifreeze.

 

just to be clear, by "hole" you mean here?: 

http://www.subaruforester.org/vbulletin/attachments/f88/7887d1188673993-whats-sensor-sensor-4.jpg

 

I've bypassed coolant hoses from throttle body before without issues, so unless you're driving to the arctic circle you can completely bypass them for testing or repair if that's helpful.  Remove inlet and outlet and just run the two lines as one.  Less fastened end joints = more reliable statistically speaking.