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After some rough idle, SES light, pulling codes, and going into limp mode at high rpm I have ordered new MAFs and all 4 CPS's

My question is, would the CPS's be easier to access if I removed the Plenum?
If I remove the plenum, should I need to get new gaskets?
Would there any other benefit to pulling the plenum, such as cleaning various sensors or throttle bodies?

Thanks
 

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If you decide to remove the plenum you're opening yourself up for a lot more maintenance work. i.e checking for vacuum leaks, icv cleaning, thermostat (makes it easier to do with plenum off), oil separator refurb.

The CPS's can be done quite easily with the plenum in place, see my DIY thread.
 

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I did mine for the 1st time a few weeks ago. I was a bit nervous about it because I'd heard how difficult it can be.

I did not remove the plenum and glad that I didn't. I did the passenger side first working from above and it took about 2 hours at a cautious pace. Getting the bracket off had me worrying about how I was going to get it back on so I saved that until later.

The driver's side proved to be a bigger challenge so I decided to try from below (FWIW I have a lift and Dinan headers.)

In 5 minutes I realized I had wasted my time working from the top.

I was able to do the driver's side mostly from below in about an hour. I bolted the passengers side bracket back on in about 15 minutes working from below.

I have only done this job one time and looking back, it was pretty easy (with a lift and headers - and fairly long arms).

The car runs much smoother now though it isn't any faster (I had no codes previously).
 
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I've replaced all 4 cps twice now, on both M5s I've had. Both times from the top, once with plenum on and the other time with the plenum removed. It was easier with the plenum removed. If you have a machanics mirror, it would help to better see what you are up against. Not very hard to do, I would give it a 5 on a scale up to 10.
 

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After some rough idle, SES light, pulling codes, and going into limp mode at high rpm I have ordered new MAFs and all 4 CPS's

My question is, would the CPS's be easier to access if I removed the Plenum?
If I remove the plenum, should I need to get new gaskets?
Would there any other benefit to pulling the plenum, such as cleaning various sensors or throttle bodies?

Thanks
You pretty much listed the big benefits of removing the plenum. Like you and others said, it's a great chance to clean the throttle bodies, ICV, but also to check for oil in the plenum. I replaced my valve cover gaskets and plenum gasket since they're cheap and were original.

Removing the plenum isn't hard. It can take a while, so just take your time and inspect things carefully while you're in there. If you ask everybody what to replace while you're in there, your list will range between a few items to a new car. For me I think oil separator hoses are a must since they're right there (if mushy), and vacuum lines depending on if you're willing to do more and spend more (use silicone lines when possible).
 

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I've replaced all 4 CPS sensors about a year ago. It is a time consuming job and requires a lot of patience, but there is no need to remove the plenum.

Good luck !
 
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