HFM is being checked on Monday.

Here are couple more symptoms that I wanted to share, just to see if it helped to diagnose.

Driving down the interstate, running fine, I'll get a "miss" almost like letting off the gas real fast. It picks right up instantly and runs fine.

I got 12 mpg on the last tank. 12.

This morning when I started it up it ran fine. I drove 15 miles. All fine. Then, sitting at a red light I'm thinking "man, this thing is idling smoothly" when right out of the blue, at idle, it started running rough and surging.

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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
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(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
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1989 Mustang GT Cobra Convertible
43k miles