Rough idle and lots of vibration after a timing belt change

My wife and I recently bought a 2005 Subaru Outback 2.5 XT with an automatic transmission. Last week, we had the timing belt changed by a mechanic I’ve gone to for the past four years and trust a great deal. He changed the timing belt, drive belts, water pump, pulleys, tensioner and a few hoses, and everything seemed to go off without a hitch. After picking up the car, though, we noticed that the idle seemed much rougher than it had in the past. We can’t tell if it’s also rough during driving, or when the car is in park or neutral, but there is definitely considerably more vibration when the car is stopped in drive and idling–you can feel it throughout the car. I haven’t noticed it until the car has warmed up.

I asked my brother, who is a mechanic in another state, if he had any thoughts, and he said it could be that the belt is off a notch, a vacuum leak or an unplugged sensor. I brought the car back to the mechanic today to see if it he could fix it, and he said that the CEL would be on if it was a vacuum leak or unplugged sensor, and that the car has an automatic idle that the belt change would not have adjusted. He asked if the vibration was getting any better, since when the battery was unplugged it would take the computer awhile to relearn the correct idle, but we’ve driven it a few hundred miles and it hasn’t gotten any better. I left the car with him to take a look at it, but he just called and said he couldn’t find anything wrong.

I want to chalk this up to us imagining something, but we both have no doubt that there has been considerably more vibration at least when the car is idling since we picked it up after the timing belt change. Is there anything else that it could be or that I should ask my mechanic?


I think the timing belt is out of time…by a notch or two. Time to take it in to a good independent mechanic and get a second opinion.

I believe you have two timing belts, one for each head, but even if they have figured out how to use a single belt on a horizontally opposed engine, there are still two (or 4) cams to time and it only takes one to be off a notch to cause a rough idle. If you engine is a VVT (variable valve timing) engine, then it is even easier to get the timing off a notch.

But there is one other possibility. If you have balance shafts, one of them could be off time. That would be more likely to me because if the cams were off timing, you should get a check engine light and notice a serious drop in power and fuel economy, enough so that you would not have forgotten to mention it in your post.

Thanks for the responses.

I could be wrong, but I think there’s one timing belt and two cams, and two drive belts–not that I know exactly what all of that means. I haven’t noticed any drop in power or fuel economy and no check engine light. I have no idea if the engine is VVT or if has balance shafts, but I’m assuming those are all controlled by the same timing belt and it’s a matter of checking the alignment on all the parts, right?

The mechanic called back about 2 hours after I dropped the car off, and I’m not sure what’s involved in checking the belt, but I’m assuming it’s pretty involved to get at, so I doubt he did it in that amount of time. I have a good history with this mechanic and they get very good reviews, but I’ll get a second opinion if necessary–I just don’t want to rack up another bill on top of an expensive timing belt job, especially if it’s just to fix the job.

Just throwing a possibility out there simply because it has been known to happen before. There’s always the offchance that someone made an error while setting the camshaft timing, did not recheck their work prior to starting, and then hit the key; only to find out that the noise heard during cranking is the sound of cylinder head valves hitting the pistons. That can lead to bent valve(s), lowered compression, and resetting the camshafts after the fact will not cure the problem.

Please understand that I’m not accusing the shop of this and it’s only presented as a theory and assuming the problem is related in some way to the timing belt change. The cam timing being off a tooth or two could also cause a problem like this without leading to cylinder head valve damage.
The cam timing being off a lot is what leads to damage.
Hopefully the scenario presented is not the case.

Hopefully that’s not the case, but is there anyway to check that easily? I’m assuming that that sort of damage would cause other issues that I’d notice besides just an unusual amount of vibration, but I don’t know. I’m assuming valve damage would be pretty obvious, but again I have no idea really.

Right now, I’m planning to go by the shop tomorrow morning to pick up my car, but instead I’m going to ask if they noticed vibration, and whether they checked the belt to make sure it wasn’t off a notch. If they didn’t, I’m going to ask them to do that since it sounds like that is the most likely culprit. Since we take public transit to work, we don’t drive the car much around town, and I’m going to see my brother in couple weeks, so if it’s not figured out by then, I’ll ask him to take a look.

Yes, the easy way is to do a compression test on each cylinder. Low or no compression on a cylinder probably means the valve is bent. Ask him to do a compression test before you take the car back.

I too am somewhat curious as to whether or not they notice the vibration and, if so, what they have to say about it.

Unfortunately, OK4450’s point does have to be on the table as a possibility and checking compression would be a way to learn something of the condition of the valves.

There is a code that should get set if the timing was not set correctly, and it is the type that really should have triggered an engine light within a few hundred miles (I would actually think pretty much immediately).

You can have all sorts of different levels of vacuum leak with no error codes, and even when you got one it wouldn’t tell you that you have a vacuum leak. (It would tell you something like the air/fuel mix is lean).

An unplugged sensor should be an immediate code.

Anyway, I just have one thought to add. I don’t know the timing belt service procedure on this car, but on many you actually have to dismount the front of the engine to one degree or another. If one or more of your mounts were left loose, it wouldn’t be the first time that happened. It’s also the case that some mounts have to be adjusted properly before they get their final torque-down. Either of these things, done improperly would give you vibration. As I said, I don’t know if either of these things applies to this model car on a timing belt job.

If the configuration of the t-belt is that it goes over two camshaft pulleys, well it is very easy to get that wrong. When it goes over only one cam shaft pulley it is smooth sailing, very difficult to get it wrong, but over two, many more ways to get it off a tooth or two. So that’s a possibility. Your mechanic could remove the timing belt cover for a look see, should be able to tell one way or another if it is off a tad.

Another possibility depends on whether the engine mount has to be removed to install the t-belt. If so, it may not have been re-installed quite right. This is easy to do as the engine tends to shift and rotate and it can be difficult to get it back in the exact orientation so that the engine mount goes back on like it was before it was removed. If it isn’t on correctly, there could be a gap which allows the engine to vibrate more than before.

edit: oh, I should add a third possibility. You may just be mis-remembering how much it vibrated before. One time I did some work on a VW Rabbit fuel injectors, and when I reinstalled them I heard a high pitch whining noise whenever I accelerated. It was just the fuel injectors. They’d always been making that noise, I just never heard them before I discovered what they sounded like when I was working on them.

If any valves are bent you should be able to hear them due to excessive valve lash caused by the valves not fully seating. This may come across as a noticeable tick or clack all depending upon how badly they’re bent.

If the engine is quiet and only runs poorly then knock on wood that the cam timing is off a bit and that is not enough to cause any cylinder head valve damage.
This is all still assuming that the problem is directly related to the timing belt installation of course.

Thanks again for all the feedback. My wife picked up the car from the garage last week, and asked our mechanic if he had noticed the vibration. He said that he noticed some, but nothing out of the ordinary, and that if the timing was off it would have triggered an engine light. I asked my brother about that for a second opinion, and he said it might not if it was only off a notch, that it depends on the sensitivity of the car and he didn’t know about it specifically in our case. But our mechanic said that he really thinks that the most likely culprit is the auto idle needing to reset (or something along those lines, this is relayed from my wife and neither of us totally understand), and that we should drive it around and see if it gets better. He said to bring it back if it doesn’t, but he didn’t check the timing belt when we brought it back in because it would have triggered a light if it was off.

We’ve driven it a bit since then, and the idle still seems rough a lot of the time, and I can’t tell if I’m feeling more vibration than before when driving or in park/neutral. But some of the time (probably not the minority), the idle seems fine with only normal level of vibration. My wife and I have no idea if that means that the timing is not off, but intuitively we’re thinking that if it was off it would be consistently rough. Most of the time, though, the idle is noticeably rougher than before, but no clanking or ticking–just the noise of the vibration, which can be fairly loud if it’s idling for very long. No question, though, that it’s usually rougher than before the timing belt replacement.

The engine mounts are a good point that I had wondered about. When I dropped the car off, the mechanic was doing a timing belt job on a similar Subaru, so he showed me the parts, and unless I really don’t know cars (a definite possibility), it looked like a portion of the engine was totally removed for the work, so it seems like it could be the engine mounts. I’m assuming that that would mean that the vibration wasn’t just when the car was idling, but might be more noticeable then.

In any case, I’m hoping to see my brother this weekend and have him take a quick look at the car. If he thinks anything’s up and the vibration hasn’t gone away by then, I’ll bring it back to our mechanic and ask him to check the timing as well as the engine mounts. I’m hoping that if it’s either of those things, it will be a quick thing for them to correct.