Sounds like the rough idle intermittent problem I've had for about a year! Temperature sensor (2 wire) is cheap, but didn't help me. The best help for me was to use fuel system cleaners several times and octane boosters. If you want to see all I did, search for Rough Idle or /Shuddering under James Scott starting last November.
Let me know if you get a magic answer! GOOD LUCK!
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Jim
1995 Laguna Blue SVX AWD L - 240K (daily driver) -
"ReBuILT" used engine at 236K miles (6/13)
2013 Veloster Red - Driver Now??Dropsprings [1/2" rear, 1" front] with Koni Strut Inserts> Magnaflow Exhaust System>
ECUTune Stage 1av1 Upgrade (from 1v4)>
ECUTune TCU MOD> Aluminum Crankshaft Pulley> Stainless Brake Lines> Phenolic Spacers>
Perforated Brake Rotors (dint like, OEM now)> SmallCar Shift Kit (resting since TCU MOD)> 7-Position Ground System>
High-Pressure Fuel Pressure Regulator (resting)> ATF Cooler & Campaign Filter> Yellow Polish Polyurethane Bushings> Pioneer Double-DIN Stereo with JL AUDIO Speakers>
Driveshaft Rebuilt with C-Clip U-Joints>
15 Min MOD>
20 Min MOD .. . (2011)
Valentine One Radar Detector with Remote Display - ucan'tseeme! 