Ok, so today I've been pulling my hair out trying to figure this stuff out.
Upon pulling out of a parking lot today into traffic my 98 forester stumbled pretty bad and a relay behind the interior fuse panel started clicking. The car acted just like it was misfiring and each time to engine would stumble the relay would click. Sometimes I'll only get one or 2 clicks and stumbles. Other times it stumbles so much that it nearly dies then the idle comes back up and then smoothes out.
The car itself drives perfectly fine, the clicking issue only shows up at idle or upon random acceleration.
I also noticed that upon a cold start the issue doesn't show up until the engine gets some heat built up in it.
Any ideas what's going on? I have a 800 mile trip coming up and I need everything ready to go.
It's only a little over a year old I believe. It holds a good charge of around 12.7v with the key off. Charging system outputs 14.4v.
It just started happening today, it's never done anything like this before. I've read everything I can about the fuel pump relay and all the threads that pertain to a similar issue never get posted in with the solution to their issues so I'm left scratching my head here.
Could a dead spot at the idle position for the TPS cause this sort of issue? If I bring the rpms up to say 1k it runs just fine. No stumbles, or surging, nothing. This only seems to happen with say 15% throttle or less?
Each time you hear the engine misfire you can hear the fuel pump relay click at nearly the exact same time, close enough that they sound like they happen together so to speak.
Ok so far I've removed the mass air flow sensor, idle air control valve, throttle position sensor, and I'll check to make sure all grounds are clean and tight because I recently did the heads few months ago. With any of the above combination unplugged it still has a misfire. All sensors above having a negative impact on the engine. Im leaning towards cam and/or crank position sensors and/or coil pack.
Well today I went to the junkyard to get some parts for a friend's truck and they had a few 98 legacys so I got a coil pack, a couple ignitor chips, and a handful of crank/cam sensors and a couple tps. Decided to just switch out all of then since they're easy to get to and it drove back just fine. Roughly 80mph for a good 30 minutes and then a bunch of start and stop traffic.
So in the next few days I'm going to slowly switch parts back to see what causes the issue. I'm leaning towards my cheapo replacement coil pack. I went with an eBay special because at the time there were no coils like I needed around my area. I'll definitely update this thread with my findings soon.
I also snagged an airbox because mine is missing a mounting foot for some reason. I suspect a quick lube place or dodgy mechanic caused that.