Sometimes a big improvement after replacing a part is not due to the part, it's due to "moving things around". This can mean that a bad connection was unplugged/plugged and thus fixed, a leak was solved by reassembling hoses and tightening clamps, etc.

A possible cause is an air or vacuum leak which the ECU can compensate for under steady conditions such as cruise or idle, but not when the throttle and engine speed and load are changing.

A couple of things to try - and cheap! Remove and clean the throttle body (TB), and when you reinstall it with a new gasket, be sure the throttle switch makes the prominent CLICK when you barely open the throttle from its closed position. Second, check the flex ducting from the Air Mass Meter to the TB. When you remove it to clean the TB, inspect all the folds for cracking and splits. The splits like to hide down in the bottom of the folds - look closely.

Similarly check the hoses to and from the Idle Control Valve.

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Bob: Son's XC70, my 83 240, 89 745 (V8) and XC60. Also '77 MGB and some old motorcycles