Hi,
My wife had a 2007 Honda Fit with 250,000 miles. Around this time, her car started to develop an idle stutter.
Symptoms:
It seemed that one or two cylinders would miss a beat at idle, while stopped at a stop light. It did not matter whether the car was cold or warmed up. It seemed to get worse with the AC on, and was steadily getting worse over time.
Research:
My wife and I looked at numerous on-line forums, looking for any information we could find regarding the idle stumble.
Things That Could Cause Stumble:
Vacuum Leak
Ignition - Plugs
IAC - Idle Air Control Valve
MAF/MAP Sensor
EGR
Throttle Body
Fuel Injectors
Things That We Checked:
Spark Plug Gap - Correct
EGR - Cleaned
Tried to identify which cylinders had stutter with timing light
Idle Stutter Still Apparent:
My wife and I decided to replace all four coil-overs at this point for $170.
Ignition Theory:
The car stumbled at idle. First thought was a lack of fuel because poor ignition can cause a mis-fire at higher throttle setting/engine loads, not at idle as we see here, thus I was thinking poor fuel control.
The injectors could not be heavily plugged because the car accelerated fine on the interstate ramps.
However, getting access to injectors required disassembly of quite a bit of hardware to get access to them. This made it an easier choice to instead get new ignition coils.
Stumble Fixed:
Putting new coils on the car *did* fix the idle stutter.
Coil Dissection:
Two of the old coil packs had a discoloration of the rubber section (center). I cut one of these coils apart to examine what it looks like inside.
It may be hard to see in this picture, but the center rubber portion used to be gray in color, and turned into a greenish tint. Just my opinion, but I wonder if heat from the poor internal connections caused the rubber to heat up and discolor?
Here is the same coil pack with the rubber connector rotated, to allow visibility inside.
As one can see from the picture below, the coil pack has three main components. The white piece looks to me like a ceramic resistor, but I did not bother testing this component.
Here is a picture looking inside the connector end of the coil pack. Notice how "dry" this metal surface looks. It is apparent that there is some type of build-up, which could reduce electrical contact.
One can see a build-up of residue on the left side of the spring (and resistor), which comes in contact with the coil contactor point.
Possible Coil Over Stumble Fix:
If one can get the rubber connector off of the coil pack, then these various electrical contact points can be cleaned and/or "oiled" to maintain a clean contact point in the future. Similarly, I provide routine maintenance on the battery terminals in the car with a small spray of WD-40, and have never seen the accumulation of white powder on the battery terminals.
Summary:
My hope is that this posting will help those who have an idle stutter to, diagnose the problem and fix it, by taking apart their coil-overs and making the necessary repairs. This will save large amounts of cash in the process, by not having to replace expensive coils.
I also hope that this coil dissection post will become a focal point in web searches, to help others that have some sort of idle stumble, and a possible way to fix it.
Side Note:
Right after we replaced the coil-overs, something in the transmission broke, leaving us stranded for a short time. If you have a Honda Fit with this many miles, you may want to start looking for a replacement. The car had been super-reliable up to this point, and I feel like we got our money's worth from it. By the way, the engine still started and ran great, with no burning of oil, using oil, leaking oil, etc.
Jim
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Idle Stutter, stumble, mis-fire, hickup, miss a beat
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