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My E39 M5 which I have had for 20 years, has developed an intermittent fault with even power delivery. This seems to happen if, say, I stop for petrol after driving for about an hour. On restarting the journey, the ride can become a bit lumpy, as it you were twitching the accelerator pedal. Sometimes it clears. The issue is usually not present the following day. I've changed the filters and the air mass sensors which have not made any difference. One theory is that this is build up of a carbon deposit inside the air flows which would require an extensive rebuild? I'm wondering if it is a failing electrical/computer part which struggles when getting hot and cold? Anybody has a similar issue?
 

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Does the twitchiness fix itself if you key cycle the vehicle? I think I may have a similar issue. Post fuel refill the car feels a little bit stumbly but then after I key cycle the vehicle it clears...never sets a MIL and is never really severe at all - almost hardly noticeable.
 

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01 Carbon/Silverstone Exhaust: Jedders-HJS high flow cats-resonator delete-Xpipe-Eisenman cans
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First thing that comes to mind is the fuel pump. How old is it? Also fuel filter. But could be a hundred other things. You need to see if any there are any codes. Regarding carbon deposits and airflow, if you are talking about secondary air, no, forget that. Carbon on valve seats maybe but don't worry about that now. Get the fault codes read out.
 

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Thanks folks - embarrassed to ask - how do you 'key cycle'. i don't get any codes - I've not replaced the fuel pump (it will be the "as supplied" version from 2001). I think stumble is a good word for it - with me its not severe, more a annoying twitch! It's odd, as I've done a 700 mile round trip without a blip! The carbon theory was from the dealership! :-/
 

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Is the check engine light on? You have had it for 20 years have you ever had any work done on the vanos boards or replaced any cam position sensors?
 

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I have pretty good records - and I think the answer is "no" I haven't done any work on either - over 20 years and 130,000 miles. i think the next step might be for me to get a good quality code reader - learn to pull the codes and check myself - to see if there are any obvious faults.
 

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Good scanner would help. You should do some reading on the board here about those topics I asked about. They often cause your type of symptoms without codes. I get you think it might be related to filling up but read the many many threads we have on these issues.
 

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Thanks for your input - this has given me plenty to read through now - one last Q - which scanner would you recommend?
 

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If you want to set up BMW specific diagnostic software on a laptop (I have found this invaluable for the M5) then Cable-Shack in the UK should be able to help. They are a forum sponsor on the bmw5 forum and seem well regarded. I haven't used them myself but they look easy to contact and appear to support what they sell. You buy the cable and get some free (for non-commercial use) software to install such as INPA and DIS. DIS will allow you to run vanos test sequences while INPA is easier to use and is good for looking at codes, fuel trims, live data, etc.

If you simply want to read and clear codes then I expect someone with experience of plug-in readers could chime in.
 

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The easiest route would be to get a Peake reader. More in depth would be INPA and ISTA. You can download for free from Easy Mike's BMW tools. And get the K+DCAN cable.
 

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Thanks for your input - this has given me plenty to read through now - one last Q - which scanner would you recommend?
I use a good scanner at the workshop, not going to recommend it though, costs way too much. What was said above is good advice but you will have to find a used Peake because they closed down. Again I would keep that for the shop. Every car should have a cheap $50 OBDII code reader in the glove box. With cell phones and the net when your car dies at the side of the road you can likely figure out how bad things are. OBDII readers are only as good as the software and the site you look the codes up on but it is a cheap way to get a vague idea of what is going on.
 
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