Dealer unable to properly diagnose problems

Update!!! See post #36 . . .

P0171, P0301, P0302, P0303, P0304. . .

These are all the codes my car has thrown over the past month or so. It all started about a month ago. I was sitting at a stoplight on a very cold night (~15 deg), idling and the CEL came on. When it came on, I did not notice the engine running any differently that normal, and continued to drive for the next couple of days expecting for the CEL to disappear. It did, and I thought nothing more of it.

A few days later, the CEL came back on again at idle (~15 deg out) and I noticed that it was idling very rough, so much so that even within the cabin it could be felt. But, if I stepped on the throttle at all, the engine revved smoothly. So at that point, I searched the threads here to find out that most likely a vacuum line had blown loose. Since the temperature had been so cold, I did not feel like removing the intercooler to inspect the vacuum hoses. So I simply checked the vacuum lines that I could access which all seemed to be fine.

So I then scheduled an appointment with the local subie dealership. I told the service advisor that it had thrown the codes twice on separate occasions when it was very cold out. They ran through their battery of tests, and could not find the cause. So they next called the tech hotline. The tech hotline said that most likely it was due to bad gas. They told this to me at which point I told them I did not think this was the problem. If it was bad gas, shouldn’t the problem manifest itself not only at idle?

Anyways, they cleared the codes and I took the car back with instructions to go through a couple tanks of gas and see if the problem went away. As expected, through my next few tanks of gas, the CEL came back on at idle when the ambient temperature was very cold (< 25 deg). Through a few of my own tests, I found that the CEL will turn off (as according to the service manuals) after so many cycles of turning on/off the engine if the code is not thrown again. I found that the engine misfires at idle both cold/warm if the ambient temperature is < 25 deg. This problem does not go away if the engine is warmed up. When the engine is misfiring, if I give it any throttle at all, it will rev smoothly without misfiring. Lastly, even when the ambient temp is < 25 deg, right at start up when the idle control valve/throttle are active to try to warm the engine up, it does not misfire. It only misfires when the engine is trying to do a low speed idle.

So, I brought the car back to the dealership two days ago and they have again concluded that the problem is due to bad gas. I finally told them that I would accept the bad gas theory if they would at least convince me that the vacuum lines are intact and connected by pulling the intercooler.

My question to you guys is, what should I do next? Although I have already written a book here, I have left out more details for the sake of space. Let me know if you have specific questions.

Cliff notes: Engine throwing codes for running lean and misfires on all cylinder only when the amb temp is very cold. Dealership is unable to properly diagnose and give me the “it’s bad gas” cop out.

P0171 Fuel trim malfunction (A/F too lean)

P0301 Cylinder 1 misfire detected

P0302 Cylinder 2 misfire detected

P0303 Cylinder 3 misfire detected

P0304 Cylinder 4 misfire detected

You've got fuel-delivery-related issues that are causing misfires on all four cylinders. So I can see their point about it possibly being bad gas (read: water in the fuel), especially if you're getting temporary gas delivery "freeze"at those temps. I don't recommend this due to the harshness of some dry gas products on the fuel system, but perhaps try a can of Dry Gas. Dry gas is essentially ethanol, so I guess you might try E85 if it's available in your area and see if that helps.

Good luck and keep us appraised.

SBT

P0171 Fuel trim malfunction (A/F too lean)

P0301 Cylinder 1 misfire detected

P0302 Cylinder 2 misfire detected

P0303 Cylinder 3 misfire detected

P0304 Cylinder 4 misfire detected

 

You've got fuel-delivery-related issues that are causing misfires on all four cylinders. So I can see their point about it possibly being bad gas (read: water in the fuel), especially if you're getting temporary gas delivery "freeze"at those temps. I don't recommend this due to the harshness of some dry gas products on the fuel system, but perhaps try a can of Dry Gas. Dry gas is essentially ethanol, so I guess you might try E85 if it's available in your area and see if that helps.

 

Good luck and keep us appraised.

SBT

The reason why I don't think its a gas issue is that it doesn't misfire on throttle. Another piece of info; I don't quite reach target boost in 3rd. Boost gauge shows ~13 psi tapering down when I was seeing ~15 psi when it was running good before. I don't have any logs so I can't tell if was severely pulling timing.

Have you tried different fuels at each fill up?

Prior to this issue, I have been religiously filling up at the Shell down the block from me, V-Power 93 octane. Since the dealership told me to try others, I also tried Mobil (twice) and also BP. The problem continued, again only when the temps dropped below ~25 degrees.

I'll update you on the dealership's progress tomorrow. . .I don't have too much hope for them though.

how many miles? maybe its time for new spark plugs?

About 16k. . .you think all four would go this early? This is on the diagnostic checklist for these engine codes but the dealer (and I for the most part) do not think it is plug/coil pack related. This issue only seems present on very cold days at idle. If it give it any throttle at all, no more misfiring.

This is a total shot in the dark, and I'm no expert...but is there an air-temp sensor in/near the MAF that could be broken? I don't know how much the A/F mix changes due to temperature, but if the ECU is getting bad incoming air temp data, maybe it's leaning out the mix erroneously?

Just a thought.

This is a total shot in the dark, and I'm no expert...but is there an air-temp sensor in/near the MAF that could be broken? I don't know how much the A/F mix changes due to temperature, but if the ECU is getting bad incoming air temp data, maybe it's leaning out the mix erroneously?

 

Just a thought.

I agree, this definitely could be an issue (and is also on the list of diagnotic checks to be performed for these trouble codes). On the first visit to the dealer for this problem, they confirmed that these sensors are operating properly. How they determined that, I do not know. I definitely should ask if they checked these sensors with their scan tool.

Mine started running rough at idle last summer, and idling low all of a sudden. I put my scanner on it, and it had a couple of pending misfire codes (I don't remember which cylinders). I continued driving it, and the "Check Engine" light came on as I pulled into the parking lot at work the next day. It had set a P0171, and had pending P03xx codes for all four cylinders. I looked for any obvious vacuum leaks and found nothing. Using the scanner, the coolant and air temp sensors and MAF checked out OK per the service manual P0171 test. I pulled off the engine cover and started the engine, hoping to hear if there was a vacuum leak. I finally found the "infamous" disconnected vacuum tee under the intercooler. This was the line that is barely visible between the intercooler and the alternator.

I was annoyed at the car, but proud of myself for finding the problem

--Steve

I bet is a bad O2 sensor. Bad O2s dont always throw O2 codes but if one is giving bad voltage readings, it wil cause the car's closed loop tuning to be off and it will throw misfire and fuel trim codes. However when you go in to open loop the car will run fine since its nut using the readings from the O2 sensor to tune the car. The car will only run poorly during idle and cruise. The car will run fine during warm up, and under load during accell. Im almost cetain that its a O2 sensor problem.

This exact problem happened to my Father's 02 Legacy gt. Poor ide and cruise, ran smoth during acceleration, CEL with misfires in all 4 cylinders. Dealer thought it was bad gas too. Changed spark plugs and wires. But it was the O2 sensor.

Mine started running rough at idle last summer, and idling low all of a sudden. I put my scanner on it, and it had a couple of pending misfire codes (I don't remember which cylinders). I continued driving it, and the "Check Engine" light came on as I pulled into the parking lot at work the next day. It had set a P0171, and had pending P03xx codes for all four cylinders. I looked for any obvious vacuum leaks and found nothing. Using the scanner, the coolant and air temp sensors and MAF checked out OK per the service manual P0171 test. I pulled off the engine cover and started the engine, hoping to hear if there was a vacuum leak. I finally found the "infamous" disconnected vacuum tee under the intercooler. This was the line that is barely visible between the intercooler and the alternator.

 

I was annoyed at the car, but proud of myself for finding the problem

 

--Steve

UPDATE: Dealer is again returning the car suspecting bad gas. I strongly suggested they pull the intercooler so that they could closely inspect both ends of all vacuum lines and they did, finding nothing. They also supposed ran through the entire diagnostic procedure ending with making a call to the Subaru tech line. This again resulted in the bad gas theory.

So at this point, I will go retrieve the car and fill up a few tanks with good gas. I highly suspect that the problem will reoccur (since nothing has changed). I asked the dealer what they would do if it does reoccur, and they did not know. Hopefully at that point, they will at least start throwing parts at her or really going through diagnostics in more detail.

I bet is a bad O2 sensor. Bad O2s dont always throw O2 codes but if one is giving bad voltage readings, it wil case the cars closed loop tuning to be off and it will throw misfire and fuel trim codes. However when you go in to open loop the car will run fine since its nut using the readings from the O2 sensor to tune the car. The car will only run poorly during idle and cruise. The car will run fine during warm up, and under load during accell. Im almost cetain that its a O2 sensor problem.

Doesn't hit target boost in 3rd when it goes to open loop. From what I can tell, it only misfires at idle, but not under load at all or when cruising.

I don't know how, but my particular problem seems related to temperature, when the ambient temp is < 25 degrees, it shows up. Otherwise, no issue. The only other test I can think of is to see it target boost is hit when temps are warm.

Doesn't hit target boost in 3rd when it goes to open loop. From what I can tell, it only misfires at idle, but not under load at all or when cruising.

 

I don't know how, but my particular problem seems related to temperature, when the ambient temp is < 25 degrees, it shows up. Otherwise, no issue. The only other test I can think of is to see it target boost is hit when temps are warm.

right. A bad O2 will only affect idle and cruise, which is why when you step on the gas, it smooths out. What Psi are you hitting in 3rd?

right. A bad O2 will only affect idle and cruise, which is why when you step on the gas, it smooths out. What Psi are you hitting in 3rd?

The reason why I don't think its a gas issue is that it doesn't misfire on throttle. Another piece of info; I don't quite reach target boost in 3rd. Boost gauge shows ~13 psi tapering down when I was seeing ~15 psi when it was running good before. I don't have any logs so I can't tell if was severely pulling timing.

Well this is a desperate measure, but you could invoke the ol' Lemon Law, depending on the details in your area. From my vague understanding, if a dealer can't fix a car in four visits (and some other detailed requirements) you can legally require them to buy back the car, or swap it for a new one, or somesuch. It would certainly irritate me to have a relatively new car spending so much time at the dealer, with nothing being done.

Good luck!

Well this is a desperate measure, but you could invoke the ol' Lemon Law, depending on the details in your area. From my vague understanding, if a dealer can't fix a car in four visits (and some other detailed requirements) you can legally require them to buy back the car, or swap it for a new one, or somesuch. It would certainly irritate me to have a relatively new car spending so much time at the dealer, with nothing being done.

 

Good luck!

I looked into that, but it's a no go. Lemon law in IL is only for cars either 12 months old or less and with 12k or less miles. In the end, I don't really want a new car, just for mine to be fixed.

13.5 psi is the factory boost target. i see no problems with hitting boost tagrets.

No argument here, except that when it was running fine, I was hitting 15 psi or so. So, it definitely seems to be running a little off.

I think I am starting to hear a slight boost leak. Paying careful attention on my way to work, I can now actually hear my my turbo spool up accompanied with a slight hissing noise (along with a slight misfire at idle today). Definitely not this loud before. I'll keep you guys updated.

They have not tried updating the ecu.

Tomorrow should be a cool morning. I will head out to do some datalogging. Hopefully it will be cold enough to misfire.

Well, the dealer called me up the other day and requested that I bring the car in for "decarbonizing" the intake valves. They promised a free loaner. Well, I brought the car in and they did what they said they would. The next day, again, I had still had the misfiring and also a new problem. . . maybe related. I noticed that if I came cruising to a stop in gear and clutched in, that the engine would rev by itself. This does not happen every time, but most of the time. It will rev to about 1500 RPM and stay there until the car comes to a stop.

I will attempt to datalog this to figure out if it is a throttle issue or something else. I think this may be related to the misfire . . .