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Old 09-02-2003, 07:20 PM
can-do can-do is offline
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Join Date: Jan 2001
Location: Tucson, Arizona
Posts: 758
'86 300E rough idle when warmed up

Greetings All,

I know your first response after reading this is to tell me to use the search to find my answer. I've been here three days using the search to get some idea as to the problem and troubleshooting plans and have tried quite a few of them today without any luck.
Here's the problem. The engine starts up fine and idles great until operating temps are achieved. When bringing the car to a stop and letting it sit for perhaps 3-4 minutes in drive it starts what I call missing, or a bumping action felt from the engine and the rpm in most cases drops from around 750 to about 500-600rpm. As you start to accelerate there is a chugging action of the engine until about 2000rpm where it then feels as if nothing at all is wrong. It being a cool day today I wondered if engine temp had any relation to the missing of the engine at idle so I kept the a/c engaged when driving which elevated the engine temp at a stand still to about 90-100c if left there in drive not moving for five or more minutes. This did indeed accelerate the missing of the engine. The things I have done today to see if perhaps these were the problem areas are as follows. I checked what I think were all the engine vacuum lines for breakage and vac most of them down to ensure the did hold a vacuum. I removed and cleaned the idle control valve. I replaced the fuse on the ovp, not bad anyway, and cleaned plug-in pins. Removed the distributor cap to check the condition, and cleaned the contact points on it. The cap didn't look to awfully bad, no carbon trails but I polished the leads with sandpaper anyways as well as the rotor edge. Seeing as this is my wife's daily driver, the only sympton of this happening wasn't gradual, but all of a sudden at a stop light that she was waiting at to change to green. Within the last 20,000 miles it has had the fuel filter changed, oil of course, several times, and techron run through it less than 3000 miles ago. Any logical ideas would be well appreciated. I'd like to troubleshoot this car again on Friday, so your input is most welcomed as well as any testing with reasonable tool means. If you think I have overlooked something, please feel free to ask as I tried to pay attention to detail as this has all occured.


"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan
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