RWD - ez fix on rough idle on damp days

Volvo RWD 900 Forum

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ez fix on rough idle on damp days 900


i had a persistent damp weather bad idle issue in my rex/regina 94 940. codes were thrown which i addressed but the damp/rainy day idle issue continued, over several years. i had excellent responses in the past from fellow bb's, but the advice didn't work for me on this issue.

i replaced with new/used items: o2 sensor, coil pack, knock sensor, rewired knock sensor with sheathed wiring, replaced spark plug wires, distributor and rotor, cps, vacuum hoses. but still persisted. (i kept most of the replaced stuff, and kept the old wiring intact for the knock sensor rewiring, just in case).

my 94 940 distributor is located by the alternator, engaged with the immediate cam shaft, not in the rear of the head (93 and earlier 940s).

symptoms were the car would start, but after a minute or two from a dead stop to driving, the car would die, and once started, would idle rough. i would need to let it warm up for about 5 minutes or longer before it would smooth out.

i even tried looking at the distr cap for moisture.

after several years of this problem, i read about using wire dry by crc. i cleaned the little residue on my cap and rotor and sprayed the rotor and cap, along with the coil pack and spark plug wires.

i don't have a bad idle issue any more, after a number of days of rainy/wet/damp days, even after letting the car sit for a few days.

certainly the damp weather caused the idle issue. on dry/sunny/warm/hot days, i never had a problem.

i don't think spraying the s/p wires and coil pack improved anything.

these symptoms for others may not be resolved by this crc spray, it worked for me.

i didn't try wd40 or other sprays on the distributor because i thought it leaves an oily residue which i didn't want on my cap or rotor. the crc spray evaporates but apparently leaves enough of a waterproof film to prevent moisture buildup, but not enough to interfere with the cap and rotor function.

it's been over a month now with a number of wet, damp, snowy days, and i read from that post that the person plans on spraying his cap and rotor in about 6 months as a pm measure. i will wait until i have this issue again just to see how long this crc spray lasts.

i plan on doing the same to my 2 240s as a preventive measure.

again, rwd volvos come through again with just a simple fix. volvos were built smarter than the people driving them, mostly, and i include myself in that description.

hope this will help others with similar symptoms.

byron golden
86 245
92 245
94 940


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New ez fix on rough idle on damp days [900]
posted by  bcg  on Mon Feb 5 14:51 CST 2018 >

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