Rough idle, P0302 and P0304

My 2005 Legacy GT has a very rough idle and recently threw both P0302 and P0304.

 

The car had a compression test and came back clean and even across all cylinders (150 +/- a few). The car also has new spark plugs (OEM), which were gapped properly.

 

Its also not burning any oil. Its stage 2 and tuned properly. Anyone have an insight into what could be going on? I'm going to try to take it to a shop Wed.

 

Thanks in advance for the help.

 

Note: Car ran great for 80 miles with new coils on 2 and 4 and now is back to the same problem. Its back at the shop with the mechanic.

I'll work on that. Would you guys recommend a leak down test? I've searched a bunch but limited info on misfire on both 2 and 4. Any help is welcome, definitely scratching my head here.

You generally only do a leak down test if it fails a compression test. How about an injector going bad? Does it run rough all the time?

I bring up the leak down test because I've heard of instances where cars pass a compression test but fail a leak down test.

 

It's running rough at idle and misfired at anything above 1/4th throttle. At half throttle it just falls on it's face acceleration wise

Yea, I'd start with basics 1st. As mentioned above check for vac/boost leak 1st, seeing how both misfires are on the same side. If no leaks then try moving coils to other side and see if mis-fire moves.

All of my rough idle and 030x codes have been either a vacuum line that came loose or bad injectors.

I have 150k on mine and have replaced two of the injectors over the last 8 months.

First showed up as a low rpm rough idle. Mechanic tried everything and finally replaced injector and issue was solved.

Second one totally died at highway speed. Felt like piston three just quit working. Terrible idle.

Thank you guys. The car is going in the shop to hit some of the basics. I'll give you an update when I know what's up!

Car is back and feels very smooth. Mechanic put 2 new coils in for 2 and 4. Sorry about starting a thread about this, I was just in a little panic about it being a major issue. Thanks for the replies, I'll make sure to return the favor

Have you replaced the black o-rings between the intake manifold and the TGV's with the new larger orange one's ?

 

 

Start there.

 

Where do you live ? In colder weather the black one's don't seal, will give rough idle and may be stall.

 

Also, when the intake manifold and TGV's are off the car, tighten all gas line clamps and clean the ground bar on the back corner of the intake manifold.

 

TGV gaskets and o-rings will run about $50.00

Well I spoke too soon. Car ran AMAZING for 80 miles after 2 new coils and then went right back to throwing those codes and running like crap.

 

Any insight into how the coils could have fixed it for only 80 miles?

isn't the drive cycle around 80miles?

if so, sounds odd it runs good until a drive cycle has been completed. I'm curious what it turns out to be.

 

best of luck.

It makes me wonder if a hose popped off or something. The mechanic is kind of stumped with this one. He said the misfire only started when the engine was fully warmed up.

How old is your timing belt? Has it ever been replaced? It is just interesting that you are throwing misfires on a specific bank (driver side). Would not hurt to check if your belt has skipped a tooth or two.

Timing belt was done 30-40k ago. Its just crazy that the same exact problem popped up again.

OK. Then check timing just to rule that out.

Have you replaced the o-rings between the intake and TGV's ?

My mechanic swapped the left and right side oil control valves and now it's running correctly. Xt2005 and others thanks for the suggestions, not trying to blow you guys off, life is just crazy around the holidays and with the phd program.

 

Anyone have any insight on why the OCVs helped when it didn't throw those codes?

If the OCV were to be at fault, I would seriously consider getting some new ones if I were you. The act of swapping them, and more than likely cleaning in the process, may have fixed the issue for now, but should be replaced. They are considered a wear item.

 

As to why they were causing your idle misfire, those with more knowledge than I will need to chime in.

 

Do you have an AP for your stage 2? Is it a v3? If so, you can set up a live monitor gauge for your OCV rates and verify they are running at the same levels of operation. Most people start seeing potential failures when they don't match.

Thanks for the responses. I do have an AP but it's a v1. I'll look at buying new OCVs today

I think Amazon has them for about $90 each. There is another thread around here somewhere that has the part numbers.

 

Be sure to wait for other, more experienced advice before plunging on the buy. I am not knowledgeable enough to give you expert advice on these cars. MrTris and MaxCapacity are among many that can give you better advice.

Will do, thanks for the convo

Does Cobb still offer the trade in on a V2 or V3 ?

 

If you can you should upgrade.

can someone tell me what is OCV?

 

and someone here mentioned some orange O rings? What O rings?

 

I have P0302 code. I changed plugs (OEM) and swapped coil btw cyl #2 and #4. Still throwing a code. Should i swap injectors first or do compression test?

Car is 2005 lgt with 150K km (not miles). ALL stock. 5MT.

Sry if i'm hijacking this thread, i can open another one if necessary.

 

Thank you!

 

p.s. I just want to add that OBDII reader showed that CEL was triggered at 1227rpm. I don't have the other data, i can provide. I noticed that CEL (with P0302 code) would trigger when i start the car. Car still runs fine, at least i haven't noticed any issues. I will try compression test first before swapping injectors.

OCV refers to the oil control valve, some tyoe of solenoid that control timing for the intake cams. There is one ocv on each side of the engine. The unit of the values you see when you log these is in degrees. They should both be in sync at all times.they can get stuck overtime where you'll notice that they're no longer in sync.

 

As for your misfire, when does it show up? Cold idle only? Warm idle only? Or both? Or at any rpm range?

 

The orange intake gaskets are the ones that go between the intake manifold and the tgvs. The old gasket type can cause misfires at cold idle when it is really cold outside. But it usually shows up on all cylinders.

 

You can swap injectors before you do the compression test. It is free for you.