My new to me '97 E420 is running a little rough on moving from rest or slowing to rest, seems to have no problem on the highway. Not a big deal but I though it wouold be smoother, any suggestions? Does the diagnostic fault reader than I made for my '95 E320 work on this engine? Should I replace the coil spark plug connectors? Would this fall under the warranty or is it maintenance? Thanks.

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85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

Not sure if your tester will work, but I would definitely check it for codes.
If no codes are found, I start the car with the coil /spark plug covers removed and unplug each electrical connector at the coils one at a time, and seeing if the idle changes, then plugging them back in one at a time.
If the idle does not change at a certain coil, then that's the one misfiring.
I then try a new spark plug, then supressor end, then coil.

Usually you will get a check engine light on with the misfire.
Also your mass airflow sensor could be acting up, or your fuel filter could be clogged, or fuel injector, but the usual culprite is the supressor end or a coil that you will find with idle and low power rough running along with a ticking noise.

The notorious check engine light is not on but it came on for an hour the other day.

__________________
85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)

air mass meter is #1 suspect

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

You wrote: My new to me '97 E420 is running a little rough on moving from rest or slowing to rest, seems to have no problem on the highway.

I suspect that it is running rough on the Highway, but since it is perhaps just one cylinder out of 8, that the rough running is not noticable.

I suggest the following (which is the least expensive to most expensive):

1. Change plugs (only use Bosch)
2. Change plug wires & boots (only use Bosch)
3. Change spark plug coil (only OEM)
4. Change MAF

I recently had the same problem on my 1998 C230, and corrected the problem using the above list starting with 4 going to 1 (learning curve). The actual fix was with number 2. However, in 6 years this is just about the only maintenance (besides oil changes) that has been done. The skill level to complete the list above is minimal and tools required very minimal. Good luck!

2. Ok, I'm going to change out the 8 spark plug connectors along with new spark plugs to star as they are usually suspect.

__________________
85 300CD Signal Red/Tan sold
83 300D Manganese Brown 109K
97 E420 Midnight Blue 197K sold
98 BMW 328i Vert White 100K, sold
95 BMW 525i White 125K, sold
93 BMW 525iT Red 193K, sold
95 E320 Green Wagon 125K, sold
94 E320 White 127K, sold
85 300SD 156K Grey (Annie), sold
84 300D Lapis Blue 170K (Judy), sold
99 ML 320 Black (lease), 1998 C230 White (lease)
00 Honda S2000 Red (lease)
86 Mercedes 300E (sold)
84 Porsche 911 Red (sold), 1965 Porsche 911 White (sold)