Rough Idle

I just finished paying some shop more than $6k to put a new shortblock in my vehicle and rebuild the heads thanks to subarus pos rings. I have only 2200 km on the new block.

Now once again I am getting a very slight rough idle. It doesn't feel like its missing; almost more like a roll. It just isn't running smoothly at idle. It seems to be OK under acceleration.

What should i look for now? Problems with the blue tee apparently cause a rough idle but apparently its quite noticable and this one is very slight (but its there I swear).

make sure all hoses are tightly attached and the intercooler and throttle body hose is tightly secure. they may have not done a boost leak test after the install which is hilarious to me, there could be a forgotten hose or leak somewhere causing a rough idle. make sure the intake was reinstalled correctly with the proper filter, make sure the coilpack plugs are snugged tight to the pack.

I checked all the vacuum and couldn't find anything.

Could it be a motor mount improperly installed when the new block was put in? I also get what sounds like a pop when accelerating from stop especially when facing downhill. Almost sounds like the clutch cable is loose, but it's brand new.

How do I check the motor mount. Couldn't find it in the service manual.

Thanks

You get under the car, (may be) remove the under trayand look up where the engine sits on the frame. The mounts are there.



What car is this ?

If it's a 05 or 06, did they replace the orange o-rings on top of the TVG's.

What are the outside air temps when you have this problem?

Check throttle plate, my car did same thing after rebuild, if you had rod knock it will cause throttle plate to have gunk on the inside. Just remove TMIC and spray it couple of times with carb cleaner keeping rpm's at 1500. See if that helps, also check for vacuum leak- just spray same cleaner around all hoses while at idle and see if RPM change while you doing that, if RPM change- you have vaccum leak.

Originally Posted by volodyalysak

Check throttle plate, my car did same thing after rebuild, if you had rod knock it will cause throttle plate to have gunk on the inside. Just remove TMIC and spray it couple of times with carb cleaner keeping rpm's at 1500. See if that helps, also check for vacuum leak- just spray same cleaner around all hoses while at idle and see if RPM change while you doing that, if RPM change- you have vaccum leak.

Thanks for the tips. When you said your car did the same thing, was it in reference to the rough idle, or to the slight pop when starting from a stop?

Idle

Not sure if what a new short block comes with, but it might be your oil control valves are sticking. Just changed those in my dad's LGT last week and the rough idle and stumbling went away and it drives a bit smoother now too.
Here's the part, and you need two. Install is easy, once you figure out you have to rotate the passenger side one to get it out

Thanks. Does anyone know how to narrow it down a little if OCVs are the problem? I don't just want to be blindly changing parts.

I am getting a smell of burnt oil. I don't know if that is also an indicator or burnt OCV though? I am not getting any CEL.

You could try cleaning the ocv valves first (link) and if it clears up a bit, they're probably the culprits. If it's no better, it doesn't cost you anything other than an hour of your time

Thanks, before I try this one more question. It idles rough immediately upon startup (ie in open loop). Does this eliminate the OCV as the culprit, or could the VVT not be returning to proper states due to the OCVs? In otherwards, could the VVT be causing the valves to be out of timing due to not returning to the default location when in open loop?

a p0011 or p0021 code would be thrown if the cam timing is off. cam advance should be zero at idle, if the cam pos sensor reads anything different than that it will throw a code. unfortunately rough idles can be a limey chap to figure out. it could be something very serious, it could be just a bad motor or tranny mount....and essentially anything in between. it's good that you're not getting any CEL's, or palpable misfires. it wouldn't hurt to pull a learning view from the ecu using the $15 vagcom cable and free learning view software so we can see what your long term fuel trims are doing. a rich or lean condition can cause some stumbling or roughness, even if the condition isnt bad enough to throw a rich or lean CEL.

Cool, as you notice I just put in a new shortblock so a little POed as this is how it started before.

Taking it to the shops yielded nothing.

Would the subaru select monitor tell me anything if I could find a shop that has it?

ssm can tell you long term fuel trims

Is there a special cable for subarus or are they all the same?