Hello,
FIrst post and I've been through a ton of the threads for this and can't find a common post with my specific issues. Sometimes when I start my car it sounds like a Subaru at idle. Then when I take off it'll run normal. Shift into second and anything over 20% throttle will make the car sputter like the timing was retarded jump off the gas and back on and it'll fix itself until I use more than 20 % throttle. After about 5 minutes of driving the pedal problem diapers and my car will always sputter/misfire at 3k then 4k and it'll stay that way to redline. Shift gears then the Subaru thing comes back for about 30 seconds then it's like the car fixes itself again and will run fine for a few minutes then the problem comes back again as if I was running on 4 cylinders. Ive replaced my valve covers and coil packs. I found a vacuum leak on the upper plenum and replaced the gasket as well. When that work was done the car ran great for about 2 days then back to this crap. I'm sick of chasing this issue. No CEL at all. No banked codes. I do however have a battery light on and brake light on the dash. I've replaced the battery and mechanic said my alternator was in fact charging the battery. I'm so lost with this. Please any help would be great. I've thought about MAF , Knock sensor, fuel pump,, clogged injector, or cam sensors but haven't done anything but clean them to no improvement.

Mods:
Stage 2 clutch and lightened flywheel
CAI
Catback exhaust
suspension.
Any help would be greatly appreciated.

 

Clogged cats?
Bad fuel injector?
Mismatched coil wires? (Happens often)
Intake and air filter clogged?

 

I've swapped around the coils from 4 and 6 and 3 and 5 just to make sure the coil packs were reinstalled correctly and they are. Do you know of a way to pin point a bad fuel injector? Clogged cats I guess could be an option I just thought it would throw a code for a bad o2 in that case..
Thanks for the reply. I'll play around with the intake today. I'll pull plugs soon to check the gap. Reading more about my issue I have a feeling it's my cam and crank sensor but idk still no CEL

edit: I cleaned my maf and it was gross. So the ruff Subaru idle has disappeared but the car still hiccups under load almost like clock work at 3500rpm.

 

Sounds like bad plugs.

 

I hope so. It kinda feels like spark break. I have noticed my car getting harder and harder to start each time since I swapped my battery. I'm thinking the alternator is going and may not be supplying the car with enough spark in the upper portion of the rev range.

 

So, this is my first post/reply in years on this forum. The problem you are describing is something similar to what I had back in 2012 or 2013. If I remember correctly, my car would seem like its driving ok, then suddenly just lose power with the brake and battery light showing up on the dash, then if I hit the gas a bit it would hesitate or seem unresponsive, then suddenly take off driving again. At that point, the car picked up very fast due to me holding the gas down. I am probably not describing the issue I had exactly as it happened a long time ago, but it is very similar to what you stated in your original post. I did not think it was anything to do with my battery or alternator since battery was new and the refurbished alternator was recently installed. When the normal test for battery and alternator were conducted, my system also showed to be operating as it should, but in actual fact... it was not. Luckily, after my forced induction build, I also had a dashdaq unit installed. It was a small digital screen where I can monitor, not only A/F or oil pressure, but OEM features on the car as well. One thing I was not looking at was battery voltage. So, I set up my dashdaq to monitor battery voltage as well. The issue occurred more so when driving, which is why a mechanic was not really able to pick up on my problem. Also, there are no OEM digital dials in the G so check battery voltage. So, when driving I noticed my battery voltage was normal until the car started acting up, which then on my dashdaq unit, I noticed the battery voltage jump up to like 16V. So, from this it seems that my alternator regulator or whatever regulates the power inside the alternator was on operating correctly and causing an overcharge, which would make the car act like it was in a sort of limp mode, but once the alternator decided to regulate normally the car drove normally. I hope this helps as this was what my issue was for me. I ended up going through 3 alternators through the company I bought my alternator through before finally getting a refund and buying a used OEM alternator.

Also, I had some minor issue with starting the car and some limp mode like issue months before that which ended up being bad ground connections. The connections looked fine, but when I got stuck I had a service guy come out and he ended up adding a new ground wire from my battery somewhere on or near the plenum as a temporary fix. Eventually I ended up getting a grounding kit and never had those kinds of issues again.

 

Well you might have a point here. My car wouldn't start at work the other day. I hooked up a jump box and nothing. So I tried to hook it up to a car to jump it off and all I got was a click. So unfortunately I had to have it towed. Mechanic called me and said the starter was shot and the alternator is bad.. So he replaced those. He also said my battery was bad.. Thats crazy because it's brand new. The last thing he said though is that my head unit is constantly on. I have a double din but to my knowledge the display turns off with the car. When I get my car back ill see where we're at with everything. Thanks for the reply.

 

It's not uncommon for the CD changer to fail and keep drawing power even though the car is turned off. This parasitic draw will absolutely DESTROY a battery.

 

So i got the call from the shop today. My alternator and starter were fried. He also said my 3 month old battery is F'd. So out of nowhere he said I drove it and it has hesitation. I said I knew and was hoping the alternator would help but he laughed on the phone telling me it's not an engine issue but a worn clutch. From my experience a slipping clutch doesn't cut fuel or hesitate in the rpms. It just keeps going in the rpm range while basically going nowhere. Is there any truth to this because I think I want to set this thing on fire haha jk...

 

No truth to it for a 6MT, slipping clutch will just free-rev the engine, it will turn off your cruise control if it slips while cruising but that's it. Will not cause ANY hesitation or fuel cut.

On a 5AT slipping clutches will limp mode the car yes since the TCM is monitoring input and output speed ratio.

 

I appreciate all your help man. I got it back today and learned my alternator bolt hole was stripped so they tapped new threads and my starter was only held on by one bolt.. Haha this car man.. So when I first started it I threw a fit because it was chugging at idle again. So I did the throttle reset and it ran smooth. The engine feels a lot better however it still misses at 4k. So we plugged up the computer and went for a ride and the computer shows no misfire when that happens. The only other thing I can think of is possibly the variable valve timing sylinoid. Btw the start and alternator are brand new and my battery and brake light are off for the first time since I've owned this. I'm going to throw a dart at this and ask if it could be a bad ground and replace them with a new grounding kit. Thoughts?