Glad to hear walnut blasting worked.
Originally Posted by kgaler
My X3 and the 135i with Dinan St2 both do that.
Kgaler: I spent 3 hours or so troubleshooting same problem, it popped up the day i got Dinan S2 tune on my 1 series. Dinan explained its normal and they're working on a software update to fix juddering/surging during hard acceleration.
Root of issue per Dinan: stock turbo BMWs have a barely noticeable surge/juddering during hard acceleration (due to some reason I can't accurately recall...something about either fuel delivery or vanos mapping - not hpfp related), when Dinan tune is applied surging/juddering is amplified to an easily noticeable level due to increased power. They said fix (software update) was coming, I waited a month or so and no fix. Went to battle to get money back and tune uninstalled, got around 85% of initial cost reimbursed. Relatively pleased with how Dinan handled it.