ZachCouch Posted June 11, 2018 Share Posted June 11, 2018 Since I bought my car (2005 Outback XT), I've noticed this inconsistent "hiccup" in the idle, and I can't find a definitive answer as to what it might be. It only shows up when the engine is warm and at a resting idle below 800-ish rpm. It's worse if the weather is hot, and doesn't really show up at all if it's cold out. Never happens when revving, accelerating, or cruising. You can't really hear it in the exhaust, but if you hold your hand in the exhaust stream you can feel it, and you can barely feel it sitting inside the car. I tried, but it doesn't show up well on recording. The best way to describe it would be to imagine the usual low rpm boxer vibration and rumble, with a slight jerk or hiccup every few seconds. (rrrrrrrrrrrputrrrrrrrrrrrputrrrrputputrrrrrrrrrrrrrrrrrput) After buying the car I ran injector cleaner, cleaned the MAF sensor, replaced the filter, replaced all four plugs, replaced both O2 sensors (trying to get rid of a P0420), and replaced both camshaft sensors when one died a couple months ago. Nothing has had any effect on the hiccup. It doesn't bother me, but if it's something detrimental I'd like to fix it. I'm not getting any misfire codes, but I'm thinking possibly a squirrely injector or coil. Link to comment Share on other sites More sharing options...
relative4 Posted June 11, 2018 Share Posted June 11, 2018 What types of scanner do you have? Link to comment Share on other sites More sharing options...
ZachCouch Posted June 11, 2018 Author Share Posted June 11, 2018 I have an el-cheapo from Harbor Freight. I also asked a guy I know who has a nice Snap-On one to check it as well, and he didn't get any misfire codes either. I had been getting camshaft sensor codes, but those went away after I replace them. I'm hoping to order an Accessport in a few weeks, I assume they can pull misfire codes? Link to comment Share on other sites More sharing options...
relative4 Posted June 11, 2018 Share Posted June 11, 2018 A misfire code is only triggered when the misfires on a single cylinder during a set sampling period exceed a set quantity. I think it's like 30 in 3 seconds or something like that. Your symptoms sound like a sub-threshold misfire. Any scanner with basic live data will show misfire counts. Your HF may have this. If not, I recommend an OBDLink Bluetooth dongle and the BtSsm app. Or, for this purpose, whatever. If you identify a misfiring cylinder, you can then start the misfire shell game. Link to comment Share on other sites More sharing options...
ZachCouch Posted June 11, 2018 Author Share Posted June 11, 2018 I didn't know that about misfire codes, thanks! My little scanner doesn't have live data, so I'll definitely be looking into a dongle (which I should have done in the first place). Can you expound on the "misfire shell game"? Link to comment Share on other sites More sharing options...
relative4 Posted June 11, 2018 Share Posted June 11, 2018 Let's say only cylinder 3 is misfiring. Swap ignition coils between cyls 1 & 3. If the misfire moves to cyl 1, replace the bad coil. If not, swap plugs, then injectors. If multiple cylinders are misfiring, the diagnostic path changes. At that point, you'll really want BtSsm. Link to comment Share on other sites More sharing options...
ZachCouch Posted June 11, 2018 Author Share Posted June 11, 2018 Ah, makes sense now. Thanks for the info! Link to comment Share on other sites More sharing options...
ehsnils Posted June 11, 2018 Share Posted June 11, 2018 Also check valve clearances - that is also a factor that sometimes can give this effect. Link to comment Share on other sites More sharing options...
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