Why 03 Outback vibrating more, higher start rev + lower idle, post belt replacement?

[mountainwalker]

Hi guys, finally getting settled in on W Coast and just wanted to say thanks again for all your help in finding our Subaru. The 2003 Subaru Outback H6 VDC we bought in N California before moving our here from the E Coast a) drove very smoothly has been a huge help in picking up all the light office furniture and supplies we had to buy for our office and home (I found the extra interior length of a wagon/crossover more helpful than the extra interior height of a small-mid SUV) . We were able to pick up every single thing we needed locally except for a couch set. It’s unbelievable what we were able to move with this car. I’ll post pictures shortly.

 

The car only needed the Serpentine belt replaced and wheel alignment and I also picked up a new set of tires. At 85K miles, we’ll probably also do the 90K servicing soon.

 

Though the car was driving very smoothly for weeks, the pre-purchase inspection garage said that the serpentine belt needed replacement - so after a few weeks, as soon as I could give up the car for a day, I had a local garage with good reviews replace the belt, and I noticed the following afterwards:

 

1) Higher revs upon start and lower revs later upon idle - I recall the engine used to be at about 1000 RPMs after start and very quiet with low vibration. Now, upon starting the car, the car seems to be revving at a higher RPM than it did before the belt replacement – about 1500 RPM – and stays there for a bit before coming down to 750 RPMs, and it’s noisier and vibrates more than before. It’s not VERY noisy and shaky, just noticeably more so than before, when it was super quiet with low vibration.

 

2) Twice right after coming off the highway to local streets, the car stalled at a red light. It started right back up, but I have no idea what caused the stall. It only happened 2 times, and only happened when the gas tank was lower - both times below 1/4 tank, one time when very low. One of those times the car was also on a hill. It never happened any other time.

 

A) Any idea what could be causing the higher revving, higher noise and vibration upon start? What could the mechanic have done to cause this? Is the timing off ? What RPM should the car be at upon start, and what should it be at after warmed up when still?

 

Any idea what caused the 2 stalls? It only happened those two times, under the same conditions – coming off highway to streets, upon the first or second red light, with the gas tank below 1/4 tank.

[nipper]

Hrmmmm

 

Since you moved, has your altitude changed dramatically? If so disconnect the battery for 1/2 hour and do a hard reset of the ECU.

 

When was the last time the PCV was changed, if ever? That little valve surprisingly with super lean burnning modern engines can cause some running issues.

 

nipper

[mountainwalker]

Hrmmmm

 

Since you moved, has your altitude changed dramatically? If so disconnect the battery for 1/2 hour and do a hard reset of the ECU.

 

When was the last time the PCV was changed, if ever? That little valve surprisingly with super lean burnning modern engines can cause some running issues.

 

nipper

 

Hi Nipper,

 

We didn't drive the car here from the E Coast, but we bought it from a seller in the mountains of the Lake Tahoe area, which is higher altitude, and the car is now mostly close to sea level. What I don't get is that before the serpentine belt was changed 2 weeks ago, I didn't experience these issues for over a month driving at the same near-sea level altitude. The car is in excellent mechanical and cosmetic condition.

 

I paid close attention today when starting, and I'd say the car was more like 1100-1200 RPM right after start - not as high as what I wrote before, but higher, a bit louder and more vibration than before the serpentine belt change.

 

What is the ECU? Is there anything else that needs to be done for the hard reset?

 

What is the PC valve?

 

Please excuse my ignorance - it's been many years since I owned a car, living in a big city with lots of public transport and within walking distance of 3 car rental places, and I haven't had a chance to read the Outback manual yet. I'll look those up tonight.

[mountainwalker]

A poster on CarTalk suggested that the rougher idle might have been caused by the mechanic knocking a vacuum hose loose or knocking a sensor slightly off. The poster also asked if the CEL is on. What’s the CEL?

 

What’s the role of the vac hose? Could a loose vac hose cause the rougher idle?

 

Also, what’s the correct idle speed of a 2003 Subaru Outback H6 after the car is warm, and what’s the correct idle speed in the first 2 minutes after starting the car?

[nipper]

Never owned and OBDII car before?

 

CEL = Check engine light. If you don not know what this is or where it is, i STRONGLY suggest you pull out the owners manual and read it cover to coever (should be mandatory anytime anyone buys a car).

 

Vacume hose well is just what it says. Its a hose that carries a vacume to the various parts of the engine and other componenets that need engine vacume to operate.

 

Cold rpm is hard to tell, depends upon what cold is? IS it 70 degrees, 50 degrees, -20 degrees.

 

normal rpm isusually btween 600-800 rpm. Most cars are 650-750.

 

Look around the air cleaner, especially under it. Look for any disconnected hoses.

 

nipper

[mountainwalker]

Having the same mechanic who worked on the car the day before the issue started take a look at it tomorrow morning, after the the weak idle while stopped was a tiny drop weaker (almost stalled once today at a light). Car driving beautifully otherwise, I'm pretty sure it's just a hose or a sensor. I'd have to say hose - almost seems like not enough air/suction getting to where it needs to be.

 

Any other possibilities you can think of besides these:

 

1) Rougher idle might have been caused by the mechanic knocking a vacuum hose loose or knocking a sensor slightly off. Check around the air cleaner, especially under it. Look for any disconnected hoses.

 

2) If the altitude has changed dramatically, the ECU might need a hard reset – disconnect the battery for ½ hour and then do a hard reseat of the ECU.

 

3) Check the PCV valve. That little valve surprisingly with super lean burning modern engines can cause some running issues.

 

Thanks again for helping troubleshoot.

[ShawnW]

I would guess he may have left the air filter box lid loose at the bottom corners and the MAP sensor isn't happy about it.

 

Mechanics tend to check a car over after they work on it for a repair. They may have popped things open to check them and such.

[mountainwalker]

So I took the car into the same mechanic who replaced the serprentine belt, along with the list of possible causes put forth here in the forum. He said he could find nothing wrong, but cleaned out the Throttle Box, which had some gunk in it, thinking that would help. The car ran with higher cold and warm idle speed and less vibration for about 5 days after.

 

Then the car started AGAIN running 50% of the time with lower warm idle speed of about 500-550, but not all the time. No idea what's causing this, but now that the previous owner's Gold Plus Subaru coverage plan transferred into my name, which covers all parts and service, I'm taking it to the best Subaru dealer in the area to run a diagnostic and fix the problem. The car drives beautifully other than this which pops up occasionally.