Who does this to cars? Finally found my BMW's running problem.

[Aaron]

I have a 1991 BMW 525i. Little 193hp 2.5l DOHC I6 with a 5-speed manual. 260,000 miles on the original motor/trans. Ever since I've gotten it it's run like poop once it warms up. No check engine light, but within about 5-10 minutes of perfect running, it'll stumble, lose most of what little power it has, etc. Very annoying to try and daily drive. I replaced the bad O2 sensor, which helped but didn't fix it, and then tried unplugging the Coolant Temp Sensor, which caused more problems (Good). Well from the advice of a fellow BMW enthusiast, checked my intake elbow that connects the MAF to the throttle body. Who does this to cars?

The first pic is how much electrical tape was wound around the elbow. I went to the junkyard, and wouldn't you know neither of the 5 series had the elbow still. I'm going to see if I can't find one online, as I think it's beyond repair. Unless someone has some electrical tape they can send me.

[Grim2.0]

They couldn't even use Duct tape, that's bullshit.

[Aaron]

Haha no kidding!

Rockauto has a brand new one for $22 shipped, can't complain about that, it's on the way. I think I'll duct tape it for additional longevity.

[sciroccojoe]

Those old beemers are incredibly dependent on a tight vacuum system. You can pull the dipstick out and just listen to the idle drop

Funny my 4runner has a had a taped up intake boot since i bought it and it hasnt really affected it at all.....its more the burnt valve robbing my power hahah

[Aaron]

The intake boot wouldn't be a problem if it was a MAP based injection, or if it was before the MAF, but since it's after I think it'd be a problem on most cars. That's a lot of un-metered air into the motor.

[bluedogok]

I had a crack on that piece on my 03 Z4 (M54) and it triggered a check engine light just before my Texas inspection was due. Had it replaced during a service, I think the piece was about $35-40. I didn't really notice it running any differently than before the light came on.

[Aaron]

Weird, it didn't trigger a check engine light (And the lamp is working properly), yet caused (Or at least I hope it caused), significant running problems. It makes sense though, under cold start the MAF sensor is disabled as it takes time to warmup, and the predicted values cause the engine to run rich on purpose (Smoother, safer, and warms the engine up quicker). So additional air wouldn't really be noticed. Whereas once it's warm and in closed loop, additional unmetered air would cause quite a running issue.

I'd think the Oxygen sensor would largely help my issue, it probably did on yours, not sure why it wasn't on mine. Maybe it did at high rpm only, since high rpm (Above 2500), it seemed to click and run perfectly. The issue was idle to 2500 when warmed up. Or maybe your aluminum block was just Godly enough to not care

[3point5]

My mom has an older (~2000) mazda protege and I did an oil change on it the intake was duct-taped patched…I laughed then I put a silicone coupler on it…

I may have a few extra couplers around if you want one…let me know what size it is -

[Aaron]

I appreciate the offer, but I ordered a new pipe for $22. Seems to have helped, but not fixed my problem entirely.

[laspariahs]

You bought a BMW with 260,000 miles on it, brave.....

[Aaron]

Original engine transmission, and this is the only issue. A/C blows cold, heater hot, and everything works. Tell me again how I'm brave? A synthetic oil change every 10,000 miles?

[big_sur]

You can keep those old BMW's running forever and they're pretty easy to work on. Anything past an e36, I would agree, but the older ones will go forever. I know of a couple e34's over 200k and you wouldn't know it as long as they're maintained.

[Aaron]

That's what mine is, a 1991 E34. First year of the indestructible DOHC I6.

[Ghosty]

Those old beemers are incredibly dependent on a tight vacuum system. You can pull the dipstick out and just listen to the idle drop.

Wow, even in the crankcase? Is that from loose clearances on the rings? Guess I'm lucky, never had a motor that cared about vacuum on the bottom end, only the intake side.