a new coil should not make it worse. Also the airflow meter is $40-80 cause all you really need is the potentiometer from bosch. I would do a search on the potentiometer cause some one found it for less than I paid for mine. The actual flow mechanism is pretty darn reliable so I doubt very much it is that, rather just the potentiometer. This stumble used to be really common on the old 450 engines and they would also stumble around 55-60 to. God I miss that engine it was so simple.

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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)