Wagon With Rough Idle
Thread Starter
Junior Member
Joined: Aug 2016
Posts: 22
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1998 E320 4matic Wagon
Wagon With Rough Idle
My '98 e320 4matic wagon with 120k miles on it has been having rough idle issues for a few months. I'm finally getting to a position where I can afford to fix it, so now I am inquiring.
When I am driving it, it doesn't vibrate. In reverse or when idling, it vibrates pretty bad. And sometimes it like, pulses. I hate pulling up to stop lights.
I love my car though.
No check engine light, or anything either.
From everything I have read, I assume it is engine OR transmission mounts. Maybe both? I know this has been asked a lot on this forum, but I thought that the pretty hard pulses were weird. Hadn't seen much about that.
Thanks!
When I am driving it, it doesn't vibrate. In reverse or when idling, it vibrates pretty bad. And sometimes it like, pulses. I hate pulling up to stop lights.
I love my car though. No check engine light, or anything either.
From everything I have read, I assume it is engine OR transmission mounts. Maybe both? I know this has been asked a lot on this forum, but I thought that the pretty hard pulses were weird. Hadn't seen much about that.
Thanks!
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Joined: Nov 2012
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A gaggle of MB's
A bit more feedback:
1) When idling in Drive/with foot on the brake - put car in neutral - in neutral does the "vibration" get less/smoother ? Foot still on the brake - move back to Drive (or Reverse) - does the vibration get harder/rougher ?
This is the diagnosis for failing/failing engine mounts - for your car there is a different mount for left and right - OE is Lemfoerder/Sach-Boge at about $85 ea from reliable internet source - China non-name/quasi-brand mounts although cheaper are to be avoided since China mounts fail very/very quickly.
2) Pulling up to a braked stop - engine RPM's drop - as it approached idle - engine seems to "choke itself" dropping below normal idle - almost stall - then "catches itself" and RPM surges up a bit above normal idle - then drops back down and almost "chokes" again - is this what you are describing as "pulses" ?
That is the diagnosis for a failing Mass Air FLow sensor (MAF) - lots/lots/lots "junk" MAF out there - at/under $75 this one appears PK:
Best at same time to replace air filter with Mann/Hengst for like $12 - and buy a bottle of Stabil Marine Fuel Stabilzer for like $9 and throw 1/2 bottle into a full tank of fuel..
Hope this is helpful.. diagnosis ALWAYS comes before action..
1) When idling in Drive/with foot on the brake - put car in neutral - in neutral does the "vibration" get less/smoother ? Foot still on the brake - move back to Drive (or Reverse) - does the vibration get harder/rougher ?
This is the diagnosis for failing/failing engine mounts - for your car there is a different mount for left and right - OE is Lemfoerder/Sach-Boge at about $85 ea from reliable internet source - China non-name/quasi-brand mounts although cheaper are to be avoided since China mounts fail very/very quickly.
2) Pulling up to a braked stop - engine RPM's drop - as it approached idle - engine seems to "choke itself" dropping below normal idle - almost stall - then "catches itself" and RPM surges up a bit above normal idle - then drops back down and almost "chokes" again - is this what you are describing as "pulses" ?
That is the diagnosis for a failing Mass Air FLow sensor (MAF) - lots/lots/lots "junk" MAF out there - at/under $75 this one appears PK:
Best at same time to replace air filter with Mann/Hengst for like $12 - and buy a bottle of Stabil Marine Fuel Stabilzer for like $9 and throw 1/2 bottle into a full tank of fuel..
Hope this is helpful.. diagnosis ALWAYS comes before action..
Thread Starter
Junior Member
Joined: Aug 2016
Posts: 22
Likes: 3
1998 E320 4matic Wagon
In Neutral the vibration does lessen, it pretty much goes away. And the vibration gets harder once I put it back in drive or in reverse.
As for the pulses, I will need to look at the RPMs the next time it does that. It's not something that happens every time I drive. And it always happens when I have to come to a quick stop/ break hard. Once I have stopped, the car starts vibrating and starts bump bump bump bump-ing for maybe 30 seconds. At that point I can't wait to get moving again because it's so annoying!
What would you say the normal idle RPM should be for my car?
As for the pulses, I will need to look at the RPMs the next time it does that. It's not something that happens every time I drive. And it always happens when I have to come to a quick stop/ break hard. Once I have stopped, the car starts vibrating and starts bump bump bump bump-ing for maybe 30 seconds. At that point I can't wait to get moving again because it's so annoying!
What would you say the normal idle RPM should be for my car?
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