Knock Knock Who's There?

HolyCrapItsFast

Drinks beer!
I agree with their explanation but I also feel the idle jumps are not normal... I was not aware of a stumble in your car till now but a tune can fix that.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
My idle is shit, and stumbles for a second when I go from idle to the slightest of throttle input, and always has been that way. I thought a tune would fix it but after 3 different tunes, I've lost patience with that option. So I just bump up the idle with my Cobb AP and all is well. It'll stay set like that unless the battery is disconnected, in which case you need to input the idle setting changes again.

I'll try to remind myself to check and post what my idle is set at exactly when I get out of work, but I
think if I remember correctly, I'm set at about 1000-1100 RPMs. Food for thought, I guess...

EDIT: I don't want to screw with the idle on my car unless I absolutely have to, but I'm trying to remember what the idle was set at from the factory. I want to say about 750 RPMs, because I believe my AP is set at "+300 RPM IDLE (A/C OFF) and +350 RPM IDLE (A/C ON)" Anyone care to chime in?

It seems like I've always known 4-cylinders to idle in the 900-1100 range, which made me initially think to move the idle up with the AP.
 

HolyCrapItsFast

Drinks beer!
My idle is shit, and stumbles for a second when I go from idle to the slightest of throttle input, and always has been that way. I thought a tune would fix it but after 3 different tunes, I've lost patience with that option. So I just bump up the idle with my Cobb AP and all is well. It'll stay set like that unless the battery is disconnected, in which case you need to input the idle setting changes again.

I'll try to remind myself to check and post what my idle is set at exactly when I get out of work, but I
think if I remember correctly, I'm set at about 1000-1100 RPMs. Food for thought, I guess...

EDIT: I don't want to screw with the idle on my car unless I absolutely have to, but I'm trying to remember what the idle was set at from the factory. I want to say about 750 RPMs, because I believe my AP is set at "+300 RPM IDLE (A/C OFF) and +350 RPM IDLE (A/C ON)" Anyone care to chime in?

It seems like I've always known 4-cylinders to idle in the 900-1100 range, which made me initially think to move the idle up with the AP.

Yes the idle is way to low on these car in particular. Not enough speed to maintain good oil pressure or flow IMO. I always bump them up to at least 850. 1000 if there are injectors and such.
 

Td_d

Commander In Chief
My two cents here:

Don't stress about knock count - what you need to be looking at is FBKC and FLKC. Knock count is used as an input in the ecu's logic (amongst other parameters) to determine whether the ECU triggers FBKC or not. You will drive yourself crazy, for no reason, stressing about knock count. There is a reason why Cyl 4 also picks up more knock count - in most roms, the per cylinder timing is bumped up on this cylinder - the theory (amongst others) is that Subaru wants the cylinder that the knock sensor is closest to to pick up knock first, in case the other cylinders are not picked up.

On the idle - it is unusual to get the dip in idle for such a new car, but on the idle at 1100 RPMs... I don't know. I've got an 09 sti on 1200cc injectors (crap ones at that) idling steady as hell at 750 RPMS. There's a whole set of variables that feed into idle stability - including your base idle timing (timing is a highly effective, almost instantaneous way to balance RPMs low down), idle stability tables, idle throttle tables, and more. I do agree however that many compromises are made for emissions on these cars, including very low idle - so bumping it up slightly doesn't hurt.

It shouldn't be an issue on a stock 2013 though (unless I missed it, and you're tuned?).
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Yes the idle is way to low on these car in particular. Not enough speed to maintain good oil pressure or flow IMO. I always bump them up to at least 850. 1000 if there are injectors and such.

Yup, I've got DW850's. Sometimes I think because my front mount and boost tubes are huge, that might have something to do with it.

My two cents here:

Don't stress about knock count - what you need to be looking at is FBKC and FLKC. Knock count is used as an input in the ecu's logic (amongst other parameters) to determine whether the ECU triggers FBKC or not. You will drive yourself crazy, for no reason, stressing about knock count. There is a reason why Cyl 4 also picks up more knock count - in most roms, the per cylinder timing is bumped up on this cylinder - the theory (amongst others) is that Subaru wants the cylinder that the knock sensor is closest to to pick up knock first, in case the other cylinders are not picked up.

On the idle - it is unusual to get the dip in idle for such a new car, but on the idle at 1100 RPMs... I don't know. I've got an 09 sti on 1200cc injectors (crap ones at that) idling steady as hell at 750 RPMS. There's a whole set of variables that feed into idle stability - including your base idle timing (timing is a highly effective, almost instantaneous way to balance RPMs low down), idle stability tables, idle throttle tables, and more. I do agree however that many compromises are made for emissions on these cars, including very low idle - so bumping it up slightly doesn't hurt.

It shouldn't be an issue on a stock 2013 though (unless I missed it, and you're tuned?).

^ Great info!
 
Well I think the problem has been found. How it happened I can only guess. The filter on the MAF feel off the Cobb Intake and I have been running filterless who know how long. Now the question is what should I do besides the obvious of put the filter back on.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Maybe clean the MAF. I cleaned mine once in my lab at work with some q-tips, alcohol, distilled water and a can of pressurized air to blow all moisture out.
You've got to be realllllllly careful not to damage the sensor element, but I'm sure you'll be fine.
 
I dont know how you would check really but damn good guess on your part about dirty injectors. Maybe knowing the dumbass variable in the equation would of helped from the get go. Funny thing was When I was at the track a few weeks ago I was thinking the intake sounded louder than normal. Duh!
 
When I installed it I did think to my self that it was odd that Cobb didnt put some type of lip on the MAF housing so that when you tightened down the hose clamp it would stop it from coming off. Oh well
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
I know what you mean. Fun fact: I had that happen to me once, where my filter popped off and I didn't notice for a few days at least. My MAF did get quite
dirty and the car started running like shit. To verify that was the problem, I looked at the MAF Voltage on the Cobb AP. It should fluctuate between 0-5V depending
on flow. It was stuck between 2.3-2.5V. After cleaning it, I rechecked during a test drive and it operated perfectly in the 0-5V range.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Also, if you ever really suspect a fuel injector is a problem and you have no other choice, there are companies where you can
send them where they will flow test them, among other things.
 

HolyCrapItsFast

Drinks beer!
Now reset your ECU. You need to reset the learned data that accumulated while the filter was off. Give it a chance to re-learn and your good.
 

Spamby

Meat Product Toy
Similar situation with an Agency Power CAI. There was a mounting tab that was welded to the tube, in between the filter and maf housing. This was a hard mount area that eventually tore away due to engine flex vs. ridged mounting point. Ripped a half dollar sized hole in the tube and I was sucking unfiltered air for who knows how long. Only noticed when I kept hearing a persistent thumping noise due to the CAI thumping around under load.
No worries and no damage. That was years ago.
 
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