1999 740il engine miss
30 days ago Driving interstate speed for 3 hours, engine started to miss. Check engine light came on, pulled over care idle was very rough, turned ingnition off, restarted, car ran smooth check engine light off. Checked codes and nothing in memory. It has repeated this 2 more times after 2 or more hours of driving. Car runs fine around town but 10 days ago engine started having a single miss that causes a jolt/thud feel in the drivers compartment. Miss/jolt seems to happen when cruising and engine starts to lug before a down shift. Never feel the jolt on acceleration. Jolt is not noted with any consistant changes, will sometimes jolt once, sometimes serveal times in a 10 second period. Tach does not show change and no check engine light comes on. No work has been done recently. This car is a dream to drive but getting a little nervous. Any ideas to check/fix so can get back to enjoying the drive. This has my mechanic and me scrathcing our heads, I have done all the wrenching excpet timeing chain guide replacement 25000 miles ago. Thanks for the help.