Although I haven't tracked down the rough idle yet, I've recently read a 93 page thread about rough idles and hesitation.
I've replaced all of the main things that cause rough idle and have yet to perform a Leak down or compression test.
After narrowing down the possible causes, I've come to the conclusion that:
It may be another vacuum leak somewhere
It may be my rear O2 sensor
It may be my Crankshaft position sensor
It may be something internal
I've only taken apart my upper intake, I have yet to dig into the lower portion. This leads me to believe there may be hoses down there that I'm unaware of, this could mean a multitude of leaks. The lower intake will be pulled apart eventually.
I went to put in a front O2 sensor and the connector was defective, it was a bad casting. I decided to force it in and see of it worked, this caused a check engine light. While this light was on the car drove amazingly, when the codes were read they showed front and rear O2 sensors. I assumed the front one being improperly connected caused the rear code as well.
When a new sensor was received, it made the light go off, but caused the car to go back to it's old ways. This led me to believe the rear O2 sensor could be a problem. This will be changed eventually.
A fellow member of Bimmerforums.com had the same issue as me and fixed it by replacing his Crankshaft position sensor. Now mind you he replaced basically everything I did.
Here's his post:
alright after trudging through 40 something pages of this, i finally got the old girl back.
it's auto 95 dasc 318ic w/ 143k.
the car would hesitate & start bucking intermittently at around 3200-3500k. it's a lot more noticeable when i try to step on it to pass someone on the highway.
but the car would start right up & idle silky smooth. there's not much of any other issues but this damn hesitation & makes it an annoyance to drive. there's no cel at all. i've scanned multiple times w/ the peake reader & nothing at all. that's when i started reading this thread.
so these are the things i've tried in the process of fixing her:
1. new plugs & boots - helped w/ the hesitation a bit. it made it less but still was there.
2. new coils (had converted over to c.o.p.) - didn't change a thing
3. new temp sensor (dme feed) - didn't change a thing
4. new o2 sensor - nope
5. new fuel pressure regulator - didn't do much
6. swapped out injectors - no change
7. cleaned crankshaft sensor - same
8. cleaned camshaft sensor (looked cleaned when pulled out) - no change
9. checked dme - no visible damage w/ it
10. changed fuel filter - nadda
11. swapped out fuel pump - nothing
12. changed cam sensor - ok for a few minutes until the hesitation returned
13. and the winner is: new crankshaft sensor
she runs like a dream now. idles even silkier smooth than before & pulls hard & obviously no more hesitation.
i was very skeptical about just keep on changing everything because i don't have deep pockets so i actually bought the cam & crankshaft sensors used. i'm glad i did cause it cost around $100 new & the cam sensor would have been a waste then. now i can buy a new crankshaft sensor if i need to later on.
good luck to everyone w/ this hesitation problem. hope this helps.
What will i do next?
One thing that happened and i forgot to mention was at least 4 of the bolts in my valve cover stripped/ spun. I need to tap and heli coil these before continuing. I believe the rough idle is partially attributed to loss of pressure in the valve cover.
I'm first planning to replace the Crankshaft position sensor to see what that does.
I'll then pull apart the lower intake, while i have the upper intake off I may remove the injector vacuum line and cap off all of the line ends. I heard from another member this help him a lot.
Finally I will replace the rear O2 sensor.
If none of this works, the research will continue.
I will definitely perform a compression test at this point followed by a leak down test.