Misfiring, poor idle, running rough after distributor cap & rotor change

[lanceboyle]

Hey all,

I just recently bought a 1982 E21 320i (197k miles) with a nice body and interior. Love it so far! I've been slowly hitting all the maintenance items I can think of. It was running a little rough when I got it, but made it home okay over ~20 miles of freeway. After changing spark plugs/wires and oil/filter/air filter, motor still struggled a bit to idle upon cold start but eventually ran great after warmed up. Then I changed the distributor cap and rotor, and now, it simply will not idle after ~30 seconds.

What's weird is that if I let it sit and get cold, and then start it, it seems to run great! Idle settles down right after starting at around 1.5-2k RPMs, but totally smooth and no misfires. After ~ 30 seconds or so, the idle speed abruptly comes down to around 950-1.1k, and then it starts to misfire. If I let it run long enough, it'll die unless you keep lightly pressing the gas. If I turn it off and re-start it, it still struggles. So odd that it's the opposite of what I was experiencing before the cap/rotor change.

I believe I've got the plugs wired to the distributor in the correct sequence (1-3-4-2, starting at the bottom near the notch on the distributor and going counterclockwise per the arrow on my distributor). Rotor is seated firmly and the distributor seems to be on firmly as well. I've verified all the plugs are connected nice and tight as well. I also noticed that the oil dipstick does smell of fuel (and didn't before) after this escapade.

So, I bought the E21 not only because I love my E91 and wanted to own a piece of history...but also because I wanted to learn and troubleshoot when necessary, so I'm totally fine with taking the time to do so. However, I'm a little lost as to what to try next. Ideas I've had:

• Isn't there a vacuum regulator of some kind that adjusts the timing once the engine warms up? Could that be the issue (not sure if this runs at idle once it gets to a certain temp)?
• Bad gulp of fuel from not being driven for some time? It had ~1/5th of a tank when I bought it and wasn't driven a ton. I filled it with premium fuel and dropped in some injector cleaner (Lucas Oil) and it seemed to like that combo before this issue. Possible fuel filter issue from gunk getting discharged?
• Somehow, is it possible I messed up the ignition timing? Seems odd as you literally can't put the cap/rotor on incorrectly, but it's the only thing I messed with, so that might make sense.
• Is it possible it was wired incorrectly to begin with, and now wiring it correctly has revealed another issue? I should have labeled the damn wires before I pulled them...I know better but failed to do it anyway. The previous owner has a mark at the top of the old distributor, which I'm guessing may have been used to indicate cylinder 1. According to every other source I can find on post-'80 North American E21s, cylinder 1 is at the bottom of the distributor (facing the passenger fender) and the 1-3-4-2 firing order goes counterclockwise.

Any guidance or wisdom you could dispense would be greatly appreciated. I did search and found a couple other posts on the forum about setting the timing, but nothing that was quite like my issue above. Thank you!

[jr02518]

Vacuum leaks, every hose on these motors gets brittle and disturbing them during the last round of changing parts could have done them in. A smoke machine and BMW's are a given.

[mxl556]

I agree with the post above- vacuum leaks will mess everything up.

Since the issue started after cap/rotor/wires/plugs I'd do the following:

First- check the vaccum hose on the distributor advance canister to make sure it did not fall off.

Second- I know it should be obvious if the cap is not on correctly, but I'd double check that. There are notches in the distributor body and the cap has tabs. Make sure it is on correctly.

I assume you used the correct Bosch/NGK spark plugs, and removed the metal tabs so OEM ignition wires fit right? Bosch ignition wires/cap/rotor, right?

If it all the above looks good, I'd start swapping old parts in one by one until the problem is gone.

Max

[amarino]

Here's some good reading to bookmark for troubleshooting and how K-Jet works:

https://drive.google.com/file/d/0BxG...ew?usp=sharing

https://drive.google.com/file/d/1jOK...ew?usp=sharing

[lanceboyle]

So, the vacuum hose was connected, but it's definitely brittle and I can see some cracks on the side. Easy enough to swap out so I will try that later tonight or tomorrow.

And yeah, I did double check the install...luckily it's pretty straightforward. And yep, used the following parts:

https://www.fcpeuro.com/products/bmw...csi-318i-wr9ds
https://www.fcpeuro.com/products/bmw...i-320i-sti-318
https://www.ecstuning.com/b-bosch-pa...111706122~bos/
https://www.ecstuning.com/b-bosch-pa...111272144~bos/

I had done the plugs/wires last week before the cap & rotor got here, and it was running well, so I'm thinking the problem is in the cap/rotor somewhere although I do still have the old plugs laying around somewhere.

Also swapped the old parts back on one at a time, and unfortunately, the issue still persists. I'm really hoping it's just that stupid hose leaking...odd that it just started after the job but certainly not impossible.

Thanks for the links as well...will definitely look over those tonight! Appreciate the help so far!

[epmedia]

Probably time for valve adjustment. The M10 valve rocker clearances tend to tighten. Source some spare nuts, washers and bolts for the eccentrics, these tend to wear/strip. The eccentrics wear as well.

15, 16, 17, 18.
https://www.realoem.com/bmw/enUS/sho...diagId=11_0391

[lanceboyle]

Thank you all for your help! Since I didn't want to be "that guy" that got it fixed and never replied...I ended up giving up and having my local independent shop have a look at it. Sure enough, it was a stupid vacuum leak. I had found/fixed the rotted distributor vacuum advance hose, but apparently I just didn't go far enough and something else was lurking. I'll dig around in there tonight and see if I can find the new hose so if anyone else has this issue, hopefully it'll help. Car's running great now! Was so stuck on the coincidence that it appeared right after the cap/rotor change that I didn't devote enough time to checking the vacuum lines. Luckily, it was a cheap fix and they took care of a couple other nuisance items while I was there.

[hotdish]

Good to hear that it's been fixed! Worn out rubber parts have probably caused 60%+ of the issues on my e21.

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