987687 Posted February 2, 2015 Share Posted February 2, 2015 Ever since it started getting cold my 2000 outback has had a weird stumble when it's cold (like below 0F...). I start it up and let it idle for a bit before driving, and while it's idling it seems to have a misfire. But it won't throw any codes. The engine will be running smoothly, then all of a sudden drop 200 rpm, run really rough, and jump back up like nothing happened. It drives perfectly fine, doesn't do this when warm, etc. It isn't getting worse or seeming to harm anything..... BUT... I'd kinda like to know what's going on here. It has new plugs and wires as of this summer, new headgaskets last month, and runs perfect when it's warm. Link to comment Share on other sites More sharing options...
Fairtax4me Posted February 2, 2015 Share Posted February 2, 2015 That does sort of sound like a misfire. Partial misfires often occur during warm-up, and because of changing idle speed and load condition the ECU may not always set a code for a misfire during the warm-up period. Since it happens when very cold I would lean towards a fuel issue. Perhaps a dirty injector or lower than normal fuel pressure. Especially since you have new plugs and wires on it. Have you had to replace the cap on the fuel pump yet? Link to comment Share on other sites More sharing options...
987687 Posted February 2, 2015 Author Share Posted February 2, 2015 That does sort of sound like a misfire. Partial misfires often occur during warm-up, and because of changing idle speed and load condition the ECU may not always set a code for a misfire during the warm-up period. Since it happens when very cold I would lean towards a fuel issue. Perhaps a dirty injector or lower than normal fuel pressure. Especially since you have new plugs and wires on it. Have you had to replace the cap on the fuel pump yet? No I haven't done the fuel pump. And I know it's something that's a ticking time bomb on any 3rd gen. Along with some other items, it's something I need to address this summer. Even so, it runs perfectly fine when it's warm. I can (and do...) run it WOT to redline without any stumbling or issues. Link to comment Share on other sites More sharing options...
Fairtax4me Posted February 2, 2015 Share Posted February 2, 2015 I put a fuel pump in a chevy truck a few weeks ago. Had a really rough cold start. If you turned the key 3-4 times to On before starting it would start then run rough for a while and occasionally stall until it warmed up. The truck would start fine once it was warm, drove fine once warm. Put a fuel pressure guage on it and it was only getting about 8-10 psi. Apples to oranges here, but the point is the pump can sometimes make enough pressure to keep the engine happy once its warm, but not supply enough to meet the fuel demand when the engine is cold. Or the pressure may be just low enough that the fuel doesn't vaporize correctly when it sprays out of the injectors. Knowing that the 00-04 cars have a common issue with the fuel pump, I would at least pull the pump and inspect the cap for cracking, or the o-ring pushing out. Link to comment Share on other sites More sharing options...
987687 Posted February 2, 2015 Author Share Posted February 2, 2015 The other thing is, I don't drive this car very often. Once or twice a week at most. But this morning it started up in -15 F first crank, no problem at all. But ya, I've been worried about the fuel pump thingy for a while, so when I get some time (and a space inside...) I'll probably look at/replace it. Link to comment Share on other sites More sharing options...
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