It seems silly to overlook, but happens to ours - heavy inside snow mat jams accelerator enough to keep throttle slightly open. Despite trimming the mat, we have to re-position it on rare occasions, as it gets twisted getting in and out. Mimics a binding throttle linkage problem.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7