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Misfire at Idle After Heavy Braking?

Hey all. I have a long story for you.

About a month back my wife and I were on our way home from dinner and when we exited the interstate I heard an awful rubbing sound coming from the engine compartment. I wasn’t quite sure what it was or how to describe it. I was concerned it was the timing belt right away. I limped it home sputtering and misfiring and listened for a moment before shutting it down.

The next day I checked all the accessories. Nothing wrong there, so I realized it must have been the timing belt. I began striping the rest down and confronted carnage. One of the bearings had gone on an idler pulley and the gear was riding the bolt. the belt had moved out of position and began to cut into the backside of the plastic cover. By some miracle it hadn’t completely snapped or jumped timing.

I replaced all pulleys, the tensioner, the water pump, and the belt. After my buddy and I got it back together it seemed fine aside from a slightly rough-ish idle for a day or two, but then the misfire got quite bad. I chugged it up to my wife’s parent’s place. We borrowed a car from them, and then I went into repair mode again. I reasoned that perhaps the plugs had fouled when the belt was messed up initially, so I replaced the plugs. Didn’t have wires on hand. Fired it back up. No bueno. Same misfire and chugging. Still borderline driveable.

So, I tore down the belt again to find that the intake cam on the passenger side was about 5 teeth off. Seemed further out than my friend and I would have left it, but I got it lined back up within a tooth and put it back together. Still no good. Still misfiring. So we tried it a couple more times. One of my helpers started to doubt the cause, but I talked him into helping me with one more reset. This time I wanted to get everything absolutely perfectly lined up. We did. I fired it up. Silky smooth, ran like a sewing machine. Put it back together and everything seemed fine. For a day or two.

The misfiring began again. It bothered me that I hadn’t managed to take care of the plug wires. I had the codes pulled and I had a steady misfire on … I think it was 4. I replaced the wires on that side and everything was back to normal. Silky smooth operation. For a couple days.

I was on my way to work and had to brake very hard to avoid an accident. Like from 70 to 0 wheel-lockingly hard. Immediately a misfire at idle returned. Doesn’t seem to be an issue when not at idle, but it’s hard to say. I guessed that it was the plug wires from the other side. I replaced those today, gave it an oil change. Still misfiring. I dropped by autozone. Codes read - misfire everywhere but 3, and I’m guessing that maybe a sensor for 3 is just messed up. The coil pack looked suspect, and I thought I’d do the PCV valve while I was at it. After replacing both the misfires continue.

I’ve yanked the battery to encourage the computer to reset. I’m at a loss at the moment. The only think I can guess is that perhaps my new tensioner is poop and I’ve jumped a tooth or two somewhere? I’m looking for guesses and wild theories here. Anything to try. I’m going to reconnect the battery shortly and if it’s still misfiring, which I’m assuming it will be, I’m going to have codes pulled again, and I’ll post them here.

Just to head this one off at the pass - I believe I got extremely lucky and did not damage the valves with the timing belt nonsense. Compression seems good, and I doubt it would have ran as well as it did as long as it did with valve damage.

Give me ideas folks! I need some help here!

I suspect that the timing is still off. I seem to recall that several Subarus required some mysterious steps to get them in time. What was your source on the procedure?

I sort of suspect that the timing is off as well, but it’s the “still” part that I object to. I had it running like a champ, no misfiring, no hesitation, no codes, no vibrations, no nothing, until that braking incident, and the misfiring resumed IMMEDIATELY after. As in I got in the car that morning, had no issues whatsoever, hit the brakes, and after I had stopped the misfire at idle began.

I just had codes pulled again. I have a knock sensor code. I’m assuming I’ll have a misfire code as well at some point, but nothing to report yet.

Here’s the thread I got most of the information from:

I’ll post some images in a moment.

What do you mean “compression seems good”? There’s only one way to determine that. If the car were mine the first thing I would do is verify the timing marks are aligned and run a compression test.
Lowered compression can affect the firing of spark plugs which in turn can affect plug wires and coils. Misfires under low compression conditions may also be erratic.

A vacuum gauge could be used as a preliminary test as a vacuum gauge is cheap and extremely easy to use by simply connecting it to a vacuum source. It will tell you in seconds if things are not up to par.

By “seems good” I mean that when I cranked the engine over by hand the compression felt “OK.” Not an official test to be sure, but that, and the fact I’ve had it running silky smooth for a couple of days on two separate occasions since the timing belt disaster are enough for me to assume that nothing ever got so out of whack that it mangled my valves, which is the only reason I’d be paying any attention to compression. So, overall, I have to be very skeptical of compression being at the root of my issue here.

I have some new codes. I have misfire on 1, 3, and 4. I also have another symptom that may be related which I forgot to mention previously. I’m noticing some dieseling or run on. Not much, not bad, but it’s not the crisp transition to “off” that I’m accustomed to.

As far as the procedure for the timing, let me describe it for you. I wasn’t able to get the belt aligned properly using any of the normally recommended procedures. Everything was too damn tight. I loosened all the pulleys to get some play and got everything lined up, then retightened the pulleys.

I posted some images of the belt before I had it aligned to show the marks I used. On the crank, the first image in the set, the circular indentation marked in red should, if I’m reading things correctly, be set to 12 O’clock to get TDC on cylinder 1. In this position, the cam sprockets for 2 and 4 on the driver side of the vehicle will be under load, 1 and 3 will turn freely. Once everything is lined up anyway. I’ve taken some pictures of that as well. There is a single notch in the intake cam pulleys on both sides of the engine. The single mark is aligned with the notch in the top of the case at 12 O’clock. At the bottom of each of those pulleys is a double mark that is aligned with a matching double mark on the exhaust pulley on both sides. When lined up, there is also a mark on each of the exhaust pulleys that will point to 3 or 9 O’clock, away from the engine, on either side.

So the above describes exactly the alignment I used. You can see marks in the images attached.

I don’t believe I will be able to check the timing on the belt until next weekend. To be clear again, the misfire is not terrible, the car is absolutely drivable, it’s basically idling rough.

Also, again, this really seems to be connected to the aggressive braking incident. If anybody has any idea how that situation could have messed up something to put me where I am now, please shoot. I need more things to check.

MCBMW wrote:
Also, again, this really seems to be connected to the aggressive braking incident. If anybody has any idea how that situation could have messed up something to put me where I am now, please shoot.

If a problem arises after hard braking, you might want to check the motor mounts.

I think I read somewhere that the engine in question is a Subaru. Other than that we have to guess at the size, age, and model car this is from.

Year, Make Model, and engine size please.

Also was there a shaft key that was not installed. Sometimes they can drop out when installing a gear/pulley. This would allow the timing to get out of sequence easy.


Sorry Yosemite, I got so caught up with the story I forgot some of the vehicle specifics. I thought they’d be there on my user flair as well.

This is a 99 Subaru Legacy Outback. It has the 2.5 DOHC EJ25 engine. Right now it has about 160k on the clock.

As for shaft keys, I haven’t heard of anything of the sort for this vehicle. Unless I’m missing something.

Also, could something with the motor mounts cause a misfire?

Bad motor mounts can cause stress (pulling or bending) on wires and tubing. and that stress can cause just about anything if the wire opens up or the tubing develops a crack.

Bad motor mounts can cause stress (pulling or bending) on wires and tubing. and that stress can cause just about anything if the wire opens up or the tubing develops a crack.

Yes…look for a vacuum leak.

I presume your timing belt configuration is one crank sprocket and two cam sprockets. That configuration is considerably more difficult to get the timing belt marks correctly aligned than the one crank/one cam sprocket config. I’ve no experience with that configuration myself, but Ray and Tom mentioned having a problem with it on the show one time on one of their customer’s cars. They had to repeat the procedure several times to get it right. As I recall , what they said, there’s a bit of a trick needed to get the slack out between the two cam pulleys before doing the crank sprocket mark alignment. So timing belt mis-alignment remains a possibility.

Given the mysteries you’ve experienced to date, might be a good idea to just update the ignition systems with new parts, at the very minimum all the high voltage wires and spark plugs. With the plugs out that would give you an opportunity to measure the compression.

Besides ignition, problems with air fuel mixture can cause misfiring. Common causes are

  • Vacuum leaks, first priority is the brake booster since yours seem to be brake related
  • MAF or MAP sensor problems
  • Fuel pressure problems
  • Clogged fuel filter or injector
  • Clogged air filter
  • Clogged cat
  • Leaks in air intake system
  • Leaks in exhaust system

If the timing belt has marks to align with each pulley’s mark the job is virtually fool proof. All that is required is getting the tension correct with the belt and pulley marks mated.

IF you noticed that the timing was off as many as 5 full teeth on the intake cam…then you need to make certain you line up those marks DEAD ON…there is no other way…Its called timing for a reason and is massively important.

Before you do anything else…make sure you have the T belt installed correctly…and then do a compression test. This is what you need to do and it will tell you if you should proceed to other repair areas. Until this is done there is no other repair you should attempt.

The results of the compression test will tell you what the next move actually IS…until then do nothing. 5 teeth off will set up a date between the pistons and valves that surely will not end well.


Ok, I finally got a chance to strip this thing down again. It had been consistently the same level of bad, but some high revving on the way to the doctor’s office this morning sent it even further out and I have time to take a look now.

I don’t have it all the way stripped down yet, but I have the side covers off and I don’t like what I see. I can accept that I may not have had it perfect, but I have more or less the same situation I began with. The driver’s side appears to be spot on with the crank. Won’t know for sure until I pull that, but it’s pretty good on the alignment. The passenger’s side is back about 3 or 4 teeth off again. I may not have done a perfect job the last time, but I know damn well I didn’t do that crappy a job.

The really interesting part to me is that the passenger side cam sprockets are still in sync with each other, but about 3 or 4 teeth back from the rest of the engine.

Could this be tensioner failure? The tensioner seems fine, but that’s the only thing I can think of. It is ABSOLUTELY jumping teeth. I just don’t know the how / why.

You said you replaced the tensioner, so it should (operative word) be OK. That’s not a guarantee, though. Like HondaBlackbird said, make sure it’s installed properly, AND in the right direction. Some only go one way.

The Dayco belt is advertised as having the timing marks. Does your new belt have timing marks @MCBMW? If so retime the engine using those marks. Using clips like these

will enable you to keep the belt at the timing marks on the pulleys as you move from side to side and when the pulleys and belt are aligned it doesn’t matter if the pulleys don’t line up with the fixed marks on the block and heads.

The ONLY kind of T Belt job…is PERFECT…any deviation is a fail…a big fail… I dont even start my engines until the t belt is accurate…not sorta…not 1 tooth…not 3 teeth off…PERFECT. This is the one and ONLY way to do that job. Anything less that perfection and you might as well throw a grenade under the hood when you hit the starter.

I pray that your valves survived this…if they did you got real lucky…screw up the exhaust side and its over over… I think you may have lucked out with retarded open intakes…which could be the best fail mode of them all…wait what am I saying…no… no…no… You cant screw up either side…even late open intakes will turn into late closing intakes…which again…sets up a date with the pistons. Neither side tolerates that much deviation. You sure youre getting a good look at just how far off you are? Ive seen one tooth off survive but not much more than that and I do these jobs Semi Daily and have done well over 300 T belts on all manner of engines.

Line everything up…turn the engine by hand 2 complete revolutions and check the marks again. Then and only then start her up. See whatchagots… Good luck.

If we were discussing anything other than valvetrain timing…you may have some wiggle room in perfection…maybe…but not here…no sir. I’ve repaired the aftermath of close enough timing belts for years…so my view is fairly steadfast. Perfection and nothing less.


Well stop praying. I wrapped up the job earlier today and everything is fine. Rather than. Relying on the factory timing marks exclusively I found a video that explains the timing markings on the belt itself. I used those to align this time as well as a tip or two from the video. Went a little smoother this time.

Car is running great. No misfire. Here’s my remaining issue though - I’ve had it running this well before. It’s jumped teeth. That’s pretty much a certainty. The tensioner seems fine, it was replaced with the rest at the initial change. Something is still rotten in Denmark though.

Anyway, if it jumps a few teeth again, I’ll be at Napa cussing up a storm.

To further soothe fears, I haven’t done many timing belts but the cam sprockets on this car are somewhat large and forgiving on being a tooth or so off. 3 teeth is still only about ~5 degrees of rotation, if that. So it runs like sxxx, but it isn’t far enough out to damage anything. I also turn the engine over by hand several times before proceeding after each alignment to ensure I’m not having any bashy crashy. Seems all good now though.