Hey all:
My 16v has a funky idle. It's fine when cold (I replaced a few sensors on the thermostat), and when warm it bounces up and down all the time. I replaced the oxygen sensor today and now it seems better, and when the idle is now perfectly level at a stop, the engine seems to shake in a subtle way as if it is sputtering. The idle is still much better than it was before the oxygen sensor replacement. My mechanic, who reset the timing of the engine because it was off, is convinced that the previous shop I took my 16v to messed up the timing totally (they replaced the timing chain and all the guide rails). Could they possibly have messed up the timing by replacing the timing chain and all the rails? How can I check this? Thanks in advance.

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1985 190E 2.3-16 Euro