Another Rough Idle Thread - Stock '06 OBXT - Did the Basics Already

I searched and read all the threads I could find about rough idle problems. My OBXT has acquired a very rough idle the past couple months (Michigan winter) when the engine is cold that’s only noticeable after the initial high idle drops down to < 1k rpm (car shakes like a diesel) for about 3-5 minutes until the coolant temp gets up to above 100°F and then it smooths out (although its still not perfect). I checked vac hoses (including the infamous blue T connector) and everything appears sound although I didn't pull the TMIC yet (only feeling with my fingers and visually inspecting). I sprayed the intake gaskets with carb cleaner multiple times with the engine cold and warm to look for leaks and nothing. I don't have a check engine light but tried to search for stored codes using evoscan and didn't find anything (not sure if there is better code reading software though). I logged idle and o2s with romraider and although idle seems a little low when its rough due to what feels like a misfire (dips down to around 675 rpm) I can't find anything wrong. The car pulls strong and clean. I cleaned the maf and reset the ecu and that didn't help.

 

My OBXT is pretty much stock with ~ 75k miles and only basic as-needed maintenance to date and I'm very nice to the car with only occasional spirited runs. I'm thinking its time for plugs, intake gaskets, and a thorough inspection of vac hoses once the TMIC core is removed. Other suggestions?

Try fuel system cleaning before the plugs. The professional ones work well and cost about $100 to get done. if its a carbon build-up problem this will help also. And Clean the MAF if you haven't done that

I read that the release candidate version of learning view can read dtc so I might try that for the heck of it. I can't believe the car doesn't have any stored codes with how rough it runs at idle. Gathering some data from learning view couldn't hurt either even though the car is pretty much stock (has a k&n panel filter).

 

I did clean the maf with maf cleaner (at least I carefully sprayed the maf inside anyway). I could try running some seafoam into the intake manifold if carbon deposits are an issue. I've done that on many other cars and had good success. Need to do some searching and see what people here think. A good fuel system cleaning (ie not off the shelf crap) wouldn't hurt either.

 

I've had my obxt for over 2 years now and although I've done tons of custom/unique work on turbo imports I hear that plugs on this boxer are a bitch and I can see why with the rear coils so close to the body.

Its not too bad doing plugs with the "right" adapters. just have a lot of short extensions and a 3/8to3/8 adapter and when you take the coils out, the tops need to go down and to the back to get them between the valve covers and frame rail

me and xt2005bonbon have our own threads about this.. we have engine issues, but I have heard injectors causing this type of issue too

I have this problem. Coming from N/A motors I thought there was an unreported misfire.

 

I've since stopped chasing the problem down and do other things with my free time.

 

The motor simply isn't going to idle smoothly and you will spend a lot of time doing everything you can to return this 7 year old car back to factor new.

 

Keep in mind if you're burning good 91 oc gas there isn't nearly the build up that you'd expect to find on a motor running cheap 87. Chevron/Shell every 4th tank goes a long way to clean internals on any motor.

 

I've done seafoam, and most other cleaners on the cars I've owned; the results were inconclusive. I don't subscribe to blasting your system with professional cleaners.

Did plugs, cleaned MAF, tried injector cleaner and different gas stations - I cannot seem to get my idle and hesitation to get better.

 

Good luck and I will watch to see what you find.

You might want to give this a try....

 

http://legacygt.com/forums/showthread.php/diy-rough-idle-cold-start-cold-temps-lgt-07-09-155325.html?t=155325&highlight=intake+manifold+gaskets

 

I had the same issue, and only happened when the car was cold and the outside temps were real low. Never had the issue in warm weather. When the car was under warrarnty I kept taking it to the dealer once it got cold out and the issues started. The dealer just kept on replacing the 02 sensors, after the 3rd time I got fed up. Found this post, bought the gaskets and problem solved. It will now idle as smooth cold or warm. It's a cheap fix and not all that hard to do. It's worth a shot for only a few bucks.

You might want to give this a try....

 

http://legacygt.com/forums/showthread.php/diy-rough-idle-cold-start-cold-temps-lgt-07-09-155325.html?t=155325&highlight=intake+manifold+gaskets

 

I had the same issue, and only happened when the car was cold and the outside temps were real low. Never had the issue in warm weather. When the car was under warrarnty I kept taking it to the dealer once it got cold out and the issues started. The dealer just kept on replacing the 02 sensors, after the 3rd time I got fed up. Found this post, bought the gaskets and problem solved. It will now idle as smooth cold or warm. It's a cheap fix and not all that hard to do. It's worth a shot for only a few bucks.

 

This is one thing I haven't done. Did you have a warm rough idle? Mine is fine in the cold, and gets worse the hotter the car.

Nope, only when cold. Once the engine warmed the gaskets would seal.

People don't want to believe it but could be the cause for a lot of the problems.

 

I replaced mine a few years back.

 

I also had my Tuner increase the idle rpm.

 

OP, Have you taken the car on a long highway drive to get everything hot and keep things clean ?

 

Do you do a lot of short trips on the your DD ?

 

I notice you don't have many miles on the car.

 

How often dose the engine see high RPM's ?

If it is the intake manifold gaskets, do the tgv delete while your at it and why are you running the stock map or stock? Burned valves are your next problem if you keep it stock and don't see high rpm's

 

Go get a tune, e85 would be better.

Yep, intake manifold gaskets are on my short list of parts to start replacing. I did thoroughly test for intake leaks cold (and warm) using carb cleaner (spray around the gaskets with engine running) which didn't show any leaks but replacing the gaskets can't hurt and it doesn't look to be too hard (probably replace the plugs at the same time).

 

Mileage was low on the car when I bought it 3 years ago (under 40k then) and I typically only drive around 10k/yr most of which is stop-go city traffic commuting where the car rarely gets above 50-60mph for seconds. I also do a couple 2000+ mile road trips with the wife/kids each year which is probably not frequent enough. Combined with occasional low-quality (always 91 or greater octane) gas that could be one contributor.

 

First thing though I'm going to pressure test the charge cooling/intake system tonight. I suspect there has got to be an intake leak I'm missing somewhere. I doubt it’s the plugs since the car seems to run clean under boost (learning view suggests I might have a little knock though).

 

I ran learning view on the drive home last night and didn't find any dtcs there either. Still need to figure out how to interpret the data though. Will do more reading there tonight. Also just installed RR a couple days ago and need to look deeper into interpreting my fuel trims, as most of my logging experience has been Mitsubishi I'm not familiar with the "A/F Correction" and "A/F Learning" terminology yet (again, need to do more reading).

 

I doubt I'm going to start doing any mods like deleting the tgv. The car is stock and I like it that way, although tweaking the OEM rom for a little smoother timing/fuel wouldn't hurt. I just haven't had any time to learn about the quirks of the subaru yet (2 little kids take a lot of time). Besides my OBXT is a 5EAT and I really miss a manual transmission so there is a chance I'll sell the car this summer anyway so I just want to get it running clean/proper again.

 

I'll pressure test tonight and see where that leads me. If that doesn't show anything obvious I'll probably order intake gaskets/plugs and run some seafoam through the bpv hose first (might help a little since the engine isn't ran hard often enough).

me and xt2005bonbon have our own threads about this.. we have engine issues

 

^ As a matter of fact, my engine is on a stand as we speak . The mechanic is going to check the heads out, especially the one on the driver side (got fairly low compression on cylinder #4). Either a burnt valve or cracked ringland @ 63k, lovely .

 

OP, it may be a good idea to do a compression/leak down test now just in case.

 

OP, it may be a good idea to do a compression/leak down test now just in case.

 

Yeah if I get to that point (replacing plugs) I'll do that assuming there is ample clearance between the valve covers and body/frame (looks like it should be ok). The noises a boxer makes is nerve wracking if you've never owned one before... I've cut apart a few oil filters already hunting for specs of copper flake just because I'm paranoid (but I do this on every car I own at least once a year).

Pressure tested last night. The little solenoid that I read afterwards was the evap check valve buzzing scared the crap out of me. After that quieted down the only leak I could find was the passenger-front corner of the tmic, which I read is the common failure point. Its not a bad leak up to 15psi, but its not great either since any leak is bad. Did a little reading on the Bullet Proof TMIC mod. Anyone know if that mod will help seal up an already slightly leaking TMIC? If I push on the TMIC end tank corner I can make the leak decrease. For under $30 of parts that seems like a good place to start, but I don't think it’s the only cause of my idle issues.

 

In better news, while I had everything apart last night I re-cleaned my maf using a different solvent (heptane), and this morning the idle seems improved. I am going to seafoam the intake tonight and add a half bottle to the gas tank as soon as I get it down to < 1/4 tank. I'll plan to change the plugs in the coming weeks if it ever warms up and do the BP TMIC mod at the same time (not a bad idea to change plugs at 75k miles anyway). Debating changing the intake gaskets since they are prone to leaking as well since I'll be in there anyway and they aren't expensive.

The $20.00 for the o-rings is a good investment. Do it.

 

Also zip tie all the vacuum hoses.

Okay, ordered everything to do the bullet proof TMIC mod, spark plugs, and intake gaskets this weekend (should get everything tomorrow or Friday). Anything else I should do while I'm in there (other than zip tie every vac hose I can find)? First time taking the TMIC off the car or anything in there really...

^ Be careful with the bolts between the TMIC and the turbo. There are two of those and they can easily strip the threads.

 

--> see http://legacygt.com/forums/showthread.php/no-more-stripped-turbo-tmic-threads-75715.html

Well, good news and not as good news. The good news is that I was able to knock out the big job this weekend. Spark plugs + TMIC bulletproofing + intake manifold gaskets + zip tied all vac lines. It was a time consuming job but I got everything done in about 6 hours from parking the car to driving it out of the garage (including fabbing the TMIC bracketry). The not-as-good news is that although the car seems to run much cleaner/smoother under boost and pull harder, it didn't change my idle as much as the second maf cleaning last week. Its still occasionally rough both cold and warm. I'll run a couple tanks of known quality gas through the tank and see if it cleans up at all (since I seafoamed it last week). If not I guess the next step is to bump my idle rpm up a hair which I think might help a lot. More troubleshooting is the next thing after that.

 

At least it was ~ $100 well spent for peace of mind.

My car had similar symptoms and it turned out to be bad valve clearances. I hope for your sake that's not the issue with your car.

I vote bump up the idle. Mines up around 900. I coast a lot, so the increase in idle rpm increases the oil pressure too.

I pulled the stock rom off the car at lunch and raised the rev limit. I'll upload my modded rom after work and see how that helps on my commute home tonight.

 

Glad I've worked with ECUflash on other platforms before... it makes things easier. Hardest part was finding those green test mode connectors since I assumed they were near the steering column like the wrx, LOL. Hope this helps and its nothing more serious!

My car had similar symptoms and it turned out to be bad valve clearances. I hope for your sake that's not the issue with your car.

 

^ Mine too apparently.

I used ecuflash to raise the A/B/C idle from 750 to 900 rpms at operating temperature and flashed it tonight. Drove it home and it seemed to not help at all with the idle cold or partially warm. I guess I need to bump the idle in the cooler temp range also(which is already pretty high) another couple hundred rpm.

 

This morning (before the idle rom tweaking) I had a cylinder #2 misfire code. Scared the crap out of me when the cruise light started flashing at me since I was WOT from a stop at the time but being really careful about how I drive. I think I'm going to do compression and leak down tests on the front 2 cyls this weekend since they are the easiest to access. After reading this post (linked below) I'm hoping I can rule out valve problems before trying things like the OCV, injectors, and coils which will cost more $ than everything else I've done so far combined.

 

http://legacygt.com/forums/showthread.php/cylinder-4-misfire-120496.html

 

A co-worker said I should check the oil screens in the heads for the AVCS which he claims can cause idle issues if they get clogged, but I thought there was only one banjo bolt filter screen that fed both the turbo and avcs? Since I'm pretty confident in the oil change history of the car I had avoided pulling the turbo banjo to examine/clean/replace the filter screen but I noticed tonight I caused a slight coolant leak at the turbo coolant feed banjo line. Probably when I was doing the intake manifold gaskets. If I'm going to pull that banjo to re-braze or replace I might as well pull the oil feed banjo too.

 

Maybe by the end of this coming weekend I can have the compression/leak down tests completed, and replace the coolant line (or fix if I can't get a fast/cheap replacement), inspect the banjo screen feed, and test the car for any further misfire codes (I'm almost affraid to do any more WOT pulls but guess its necessary to test).

Not on my legacy but friends we had the same idle problem, replaced the intake o-rings, replaced the plugs and even the coils, did the professional fuel system treatment. In the end it was a vac leak in one of the rubber hoses going to the intake. I know you already checked that but just be sure there is no leak, maybe have it smoked tested or test it with soapy water and see if the idle goes up. Other than that.... my next step would be not only a compression test but as you said a Cyl leak down test. I used to find leaky valves that way on cars and it works for finding them. If you do have a leaky valve though, i would deff try do a real good Sea Foam Clean or have it pro carbon cleaned at a shop as was mention before , just to be sure before you decide to have any head work done.