Misfire at idle, in gear, on rainy days
03-30-2014, 12:38 PM
#1
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Location: Longwood, FL
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Misfire at idle, in gear, on rainy days I have a 98 Z28 A4. Since getting the car, it's always had a slight, random, intermittent misfire at idle. It would almost fall into the category of "rough idle" rather than misfire. I would also get a random hesitation when accelerating with the pedal at the same position, as if I was rolling my foot partly off, then back onto the throttle.
I am in Florida. The first time we had several days of rain, after about the 2nd day of driving to/from work, I would get a nearly constant, hard misfire in gear at idle, which seemed to mostly smooth out while accelerating.
This was the motivation for me to change the wires. I installed a set of GMPP red wires, and didn't notice any difference in the slight misfire/rough idle when dry. Since then, the first time we had days of heavy rain was the last few days. Sure enough, like clockwork, on the 2nd day it started hard misfiring exactly like before the wires.
In the interim before I changed the wires, I noticed my PCV hose was leaking badly, and was in about 8 pieces
Replaced that with the cheaper one for a vette. Throttle response became a lot better, and I swear I got some low end torque back. But it did nothing for the misfiring.
What are the common reasons which might cause my problem only when wet? I would assume whatever is causing my slight misfire when dry + hesitation has something to do with the worse misfire when wet. I have even checked under the hood immediately after the misfire, and was unable to find anything wet.
I am in Florida. The first time we had several days of rain, after about the 2nd day of driving to/from work, I would get a nearly constant, hard misfire in gear at idle, which seemed to mostly smooth out while accelerating.
This was the motivation for me to change the wires. I installed a set of GMPP red wires, and didn't notice any difference in the slight misfire/rough idle when dry. Since then, the first time we had days of heavy rain was the last few days. Sure enough, like clockwork, on the 2nd day it started hard misfiring exactly like before the wires.
In the interim before I changed the wires, I noticed my PCV hose was leaking badly, and was in about 8 pieces
Replaced that with the cheaper one for a vette. Throttle response became a lot better, and I swear I got some low end torque back. But it did nothing for the misfiring.What are the common reasons which might cause my problem only when wet? I would assume whatever is causing my slight misfire when dry + hesitation has something to do with the worse misfire when wet. I have even checked under the hood immediately after the misfire, and was unable to find anything wet.
04-03-2014, 03:26 PM
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Yep, sounds odd but definitely check out your o2 sensors. Every time it rained, my car would misfire to the point that I wanted to wrap it around a pole! Changed plugs=no change. Changed to MSD wires=no change. Changed o2 sensors=problem solved! After taking the old ones out, the harnesses were pretty chewed up and frayed, and were definitely getting wet.
04-03-2014, 07:18 PM
#4
10 Second Club
could be a slightly cracked coil. I had a truck do that once, and only in the rain. so in the dark I opened the hood and lightly fogged the engine with water. then I seen sparks arcing out of the coil. changed it and problem solved.
