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Discussion Starter #1 (Edited)
I'm not a huge car guy... Changed oil on a few different cars I've owned, installed exhaust on an 05 Mustang, nothing that a guy with a few tools and access to YouTube can't do.

With that said, I'm not much for diagnosing issues.

I recently bought an '05 BMW 545i as a "hold-me-over" vehicle. It has 134K miles. The body is super clean, looks clean under the hood, and CarFax was clear. It was priced right, I had the equity in my old car, and I'm going to order a new car later this year. This was supposed to be something for me to drive with no payments until my new car comes in, probably in mid-2017.

As is the risk buying any used vehicle I noticed an issue after only about 100 miles that wasn't present during the test drive. The vehicle runs very smooth. It shifts smooth, I feel like the accelerator is responsive, and the average MPG shown by the on board computer is about 22mpg.

I started to notice, however, when I come to a stop at a red light or stop sign (basically when I'm stopped with the vehicle in gear) the car will shudder. It's not extreme but the idle is around 750rpm and it basically just shakes when I'm sitting still. As soon as I take off it smooths out and there are no issues while the vehicle is moving.

I know a possible source is the engine mounts. I haven't tried a hard acceleration from stop followed by abruptly letting off the gas to see if the engine "clunks" as it sits back in place. I will try that this afternoon. Until then, or in spite of that, does anybody have any other ideas as to what my issue could be?

**Adt'l info** So the issue seems to occur only when the engine is hot. When I drive after it's been sitting for a while it's fine. If I go somewhere, say the store or the bank, and shut the engine off for only a few minutes before starting back again, the issue returns. PLEASE HELP!

No smoke from exhaust, coolant levels are consistent, oil levels are normal, SES light on
 

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Discussion Starter #2
Add'l info... I went to the grocery store this morning after I dropped off some clothes at the dry-cleaner. From the house to the cleaner to the grocery store I didn't notice the issue. I turned off the car while waiting for Wal-Mart grocery pick-up folks to bring my stuff to my car (yeah, I'm that guy). When I fired it back up and started to leave I noticed it again, all the way back to the house
 

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if the SES light is on then see what codes are present. Sounds like a misfire.
 

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Discussion Starter #5
By misfire do you mean spark plugs/coil? I tried going by O'Reillys to have them read the codes but the old man who helped me was scared to plug it in. Apparently the machine he had had a different connector or something, I'm not entirely sure but he wouldn't do it. I guess I'll go to auto zone.
 

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If it's a misfire, you could need new coils, spark plugs, or injectors.
 

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A bunch of other things can cause a misfire too, but jayR04 listed the most common causes. Loss of vacuum can cause a bad idle. A common problem with leaking seals in our cars is the loss of vacuum in extreme cases. both ways get codes pulled before you throw parts at the car. Sorry to tell you this but you chose a car thats not "something for me to drive with no payments until my new car comes in". These cars are "reliable in a German way" but they do love garages. They aren't hondas. Also the V8s, huge labor costs with everything as everything is a pain to get too. 134,000 miles is the point at which a bunch of payments on the car are going to start pilling in. Really if this car isn't a keeper I wouldn't count on not paying anything for a year on maintenance.
 

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While a misfire could be definitely cause a shake, misfires don't typically happen when the car is at idle and then go away when you start tot accelerate. It's actually the opposite that happens, there might be a slight misfire at idle but develops into a constant misfire as soon as you start tot accelerate.
 

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Misfires can happen at idle. Mostly caused by a vacumm leak. The only reason a missfire is more appetent at high revs is because the ecm switchs off the particular cylinder that is having "constant" misfires. In fact small single random misfires occur mostly at idle and sometimes wont even trigger a fault if they arent "constant" enough. Try and diagnose an old engine and you wake the engine up from a misfire by revving it. If it sticks your having an ignition issue. You cant do the same on our newer engines as the ecm/ecu turns off ignition and fuel supply on that particular cylinder in a bid to protect the catalyzer from unburnt or late burn fuel.
 

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Discussion Starter #10
I went to Autozone and thankfully the gentleman that helped me there was a little more competent then the old timer at O'Reilly's. Nothing against the old timer, you could just tell he wasn't too hip on the technology side of things... He was more of a "take that thing apart and find out what's wrong with it" kind of guy, which I respect.

So the SES codes were P0491 Secondary Air Injection System (Bank 1); and P0022 Intake Camshaft Position Timing - Over-Retarded (Bank 2). I'm guessing the "rough idle" is caused by the P0022. Any suggestions on how to proceed from here?? (And yes, I know both issues should be fixed)

On a side note I feel I should clarify something so I don't look like a complete fool... When I said that I'm not a car guy I mean that I'm not real keen on the technical terms associated with the mechanical aspect of cars. I'm not a complete idiot, if you were to tell me that my problem was the flux capacitor I would tell you to pound sand... But my knowledge is extremely limited. I completely understand that with any vehicle the more miles you have the more mechanical issues will pop up. I also completely understand that cars like BMW's are very expensive to maintain. When I say that this is a car to just hold me over I really mean it... I have a work assigned vehicle so in the year or so that I have this car I MIGHT put 4,000 miles on it. I wouldn't even have a car in the interim if it wasn't for the two or three 4 mile round trips I have to make a week.
 

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secondary air injection can cause a rough idle for sure. On my old mercs it would always mean shot vacuum lines. On the 545i it can be much more then that as the engine has an issue with its secondary injection system. I dont know too much about it but there are a bunch of posts on the forum about it. 4,000 miles is nothing to worry about, a couple 4 mile trips a week is nothing for these cars in that case.
 

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Misfires can happen at idle. Mostly caused by a vacumm leak. The only reason a missfire is more appetent at high revs is because the ecm switchs off the particular cylinder that is having "constant" misfires. In fact small single random misfires occur mostly at idle and sometimes wont even trigger a fault if they arent "constant" enough. Try and diagnose an old engine and you wake the engine up from a misfire by revving it. If it sticks your having an ignition issue. You cant do the same on our newer engines as the ecm/ecu turns off ignition and fuel supply on that particular cylinder in a bid to protect the catalyzer from unburnt or late burn fuel.
Yes misfires can happen at idle but lets not confuse a misfire with a rough idle as they are not the same thing.

A lean issue at idle definitely can cause a misfire if the lean issue is severe enough. The cause of the lean issue is the important part here. A lean misfire at idle that is caused by a vacuum leak will typically go away once the engine rpm is increased because vacuum leaks cause more issues at low rpms. Now if you have a lean condition due to something other than a vacuum leak the misfire can continue off of idle.

The real reason that misfires are more pronounced at higher rpms is quite simple, the ignition system is under more load. At idle the engine is not really under any load and therefore the ignition system is not working hard. Once engine load increases the ignition system is put under more stress and has to deliver more energy to fire the spark plug. This is when we start to feel the lack of spark which results in incomplete combustion. If the misfire is severe enough then the injector will get shut off to save the cat but the ignition still remains active so that any fuel that is in the cylinder can get the chance to ignite.
 

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Yes misfires can happen at idle but lets not confuse a misfire with a rough idle as they are not the same thing.

A lean issue at idle definitely can cause a misfire if the lean issue is severe enough. The cause of the lean issue is the important part here. A lean misfire at idle that is caused by a vacuum leak will typically go away once the engine rpm is increased because vacuum leaks cause more issues at low rpms. Now if you have a lean condition due to something other than a vacuum leak the misfire can continue off of idle.

The real reason that misfires are more pronounced at higher rpms is quite simple, the ignition system is under more load. At idle the engine is not really under any load and therefore the ignition system is not working hard. Once engine load increases the ignition system is put under more stress and has to deliver more energy to fire the spark plug. This is when we start to feel the lack of spark which results in incomplete combustion. If the misfire is severe enough then the injector will get shut off to save the cat but the ignition still remains active so that any fuel that is in the cylinder can get the chance to ignite.
I seem to have confused lean with misfire at idle. Thanks for the insight.
 
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