94 E420 - Rough idle, but drives great on the interstate - PeachParts Mercedes-Benz Forum

Ferdman · #1 12-08-2009, 04:19 PM

The proper spark plug for the E420 engine is a Bosch F8DC4, a non-resistor spark plug. Other type spark plugs could cause problems. Listen for clicking of the OVP relay ... that can cause a rough idle, at least it did in our 1995 E320.

00integravtec · #2 12-11-2009, 09:49 PM

Quote:

Originally Posted by Ferdman

The proper spark plug for the E420 engine is a Bosch F8DC4, a non-resistor spark plug. Other type spark plugs could cause problems. Listen for clicking of the OVP relay ... that can cause a rough idle, at least it did in our 1995 E320.

What is the OVP relay?

Ferdman · #3 12-12-2009, 06:19 AM

OVP is the over-voltage protective relay, but I misspoke because I checked a parts website and a 1994 E420 does not have one. So that cannot be your problem. On a 1995 E320 the OVP is behind the battery in the engine compartment.