95 E320 Stumbling Idle Update

[duc4208]

I just fixed the stumbling idle in my car. My car had been stumble at idle for several months. Brought my car to dealer two times, they could not fix the problem but cost me a bundle of money. Third time, they suggected to replaced 3 ignition coils, three ignition coil boots, spark plugs and spark plug wires and would cost me $750 or more. I told them if they could guarantee this time that they would fix the problem I would willing to pay for it. They said they could not guarantee. I was very upset and brought the car home trying to fix it myself. Post my car problem in this forum on 9/13/02 and was suggested to replace the ignition coils boots. Here how I fix my car's problem.

1. Took the ignition coils out and measure the primary side resistant of each coils. It was 0.7 ohm and they were consistent between 3 coils. Measure the secondary resistant of the coil between the connectior to the boots and the connector to the spark plug wire and it was 6.8 kohm and they are consistent with other coils. Three coils must be fine. No thing wrong with the coils. Do not need to replace with the new ones.

2. Measure the spark plug wires and they were 1.80 - 2.1 k ohm. They did not have any crack in the insulation. They must be fine and no need to replace.

3. Measure the spark plug and found out that I replaced with the wrong ones (the resistance spark plug). The resistant between the electrode and the top of the spark plug was 14000 ohm. Too much resistant was not good. Replaced with the Bosch copper spark plugs.

4. The problem now seem to be the boots. When I replaced the spark plugs, I did not replace the boots. What made it worst was that somebody might take the boots off many times. The boot become loose and lost it contact to the spark plugs and that why the car had misfire at idle in one of those three cylinders. This problem is intermittent. I finally replaced the boots and it corrected the problem.

Thanks to all of you for sharing your ideas fixing this problem. Specially thanks to Arthur Dalton for his advise to change the boots first before doing any thing else. I just want to share my experience to someone who may have the same problem that I had. Hopefully this will help to identify the component that causes the misfire at idle.