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Message: <blockquote data-quote="Autochild" data-source="post: 108891" data-attributes="member: 2084">I am not positive on what the cause is.. but will offer some pointers.. and ask a few more questions..You said after a decarb.. how was it done? it may be a simple coincidence or could have improved the performance to a point where something else gave way.. anyhow,   Sometimes it can spoil spark plugs ..depending what chemical was used.. . To see if chemical contamination occurred on the plugs look for Red color burn on them. This can also occur after using octane boosters.Have you had the car scanned for fault codes? Any appear?erratic idling often comes from a vacuum leak, either from a valve or hose or intake manifold seal. Sometimes easy to find.. other times damn near impossible.. being an older car the possibilities of it being a hose or external vacuum circuit valve are increased.. sometimes the hose looks fine.. but an end can be stretched and flared allowing air in..Does the Idle float up and down consistently? sometimes worse than other times? if you are decelerating from high speeds do you here "popping" in the exhaust.Other times erratic idle can be caused by an over tensioned throttle cable.Does the exhaust smell rich.. like it has a petrol smell?How do the brakes feel? are they consistent in peddle feel? There are other things that could be a cause.. including contamination on the MAF sensor. take note also.. often when these BMW's have a vacuum leak it will show an O2 sensor error.. but changing the O2 sensor will not fix the root cause .. there are allot of other things to rule out before changing any sensors if there is no permanent fault being recorded from them... the above are the first places to look IMHO. Peace,Autochild</blockquote>

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