The Stumble/Stutter Thread

From the very first post (which is referencing an 05)

"Let's define stumble/stutter as any form of hesitation at part throttle at either steady throttle input or increasing throttle input."

 

For many cars this "hesitation" can be attributed to the transition from closed loop to open loop.

So "the cause" that I asked about is the transition from closed loop to open loop?

Sometimes. For some it has never been figured out. Hence threads like this one. But usually a tune helps tremendously.

ok thanks!

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:

 

MODS

Intake: AVO

Exhaust: Autospeed

Fuel: 93 and E85

Turbo: AVO380

Engine Management: Cobb AP

Tuner and revision of tune(if you don't mind): Calvin Dotson Cobb Plano Protuned

 

MAINTENANCE

Sensors changed: MAF no difference

Plugs changed: 25K on plugs

Coil Packs changed:

 

OTHER SYMPTOMS

Check Engine Light: NO

Etc:

 

RESULTS

What has and hasn't worked for you: Nothings worked

If something worked, how long has it been working for:

 

My car is doing this as well. I noticed that if I ever so slightly push on the pedal and watch the Throttle position on the AP it actually goes down for a split second before it increases.

 

For example at idle with no input it is sitting at say 6. As soon as I just barely press on the pedal it goes to like a 3-4 before going up and the AFR goes a bit rich and then it hunts for a second.

 

Myself and KCwagon have the same exact issue. Once it goes rich like that as the throttle position number goes down then it is out of whack for a bit until it settles in.

Both of us were tuned at Cobb Plano, but I would think this portion of the tune was not touched.

 

Sometimes I wonder if its an issue at the throttle body or the sensor on the pedel causing this, but its weird that both of us are having the same issue.

 

If I hold the throttle at the point when the TP number goes down a bit the car really starts idling rough and will almost die.

 

Its like it does not like this partial throttle and who knows what the number going down does.

 

Anyone else have this or can test it?

 

I just went on the AP monitor section and monitored throttle position while pushing the pedal ever so slightly with my hand.

 

 

 

Car is fixed. Swapped OCV for the AVCS today and car is running great!!!

 

Mine was mostly a stuble stutter when first taking off. Didn't do it all the time and in the winter it was better, not perfect but better.

 

I finally got around to getting my ATR software going with my AP and monitored some ECU parameters.

 

Found the AVCS ALL OVER THE PLACE.

 

I sometimes would get crazy numbers like 40 sitting still at an idle just reving up the motor a bit.

 

The two banks were not the same at times and my idle at times was terrible.

 

So today I put new plugs in, and the old ones looked real good.

 

But the real change was new OCV for the AVCS.

 

Once I put these in my car it is running great.

 

Those dang things affected my fuel trims B and C, had some knock once and a while, some roughness cylinder in each cylinder once in a while.

 

I found that when I had these problems (very intermittent) the AVCS was all whacked out.

Edited June 10, 2013 by Scooby2.5

Info posted in the product description on our website

 

Oil Control Valves

 

http://www.infamousperformance.net/servlet/the-1136/Subaru-Legacy-GT-Oil/Detail

 

Oil Control Valve is the term for the solenoid valves that regulate the oil pressure driving the intake cam sprockets to clock themselves relative to the camshaft. In one position the OCVs will pressurize the system to advance the cam timing, another position to retard the timing, and the final position to lock the sprocket in place.

 

Common symptoms that may be a sign that these need to be replaced include:

-a P0011 / P0021 fault code

-rough idle

-stumbling at low rpm

-stalling

how deep in the engine is this valve?

how deep in the engine is this valve?

 

http://legacygt.com/forums/showpost.php?p=1943328&postcount=8

This might be worth a shot..

A couple of weeks ago, I had the traction light come on, the check engine light came on, and the cruise light started blinking all at once. I turned around and drove straight to the dealer. Back in February, when this happened, it turned out to be the Oil Control Valve. The dealer made mention that they would go ahead and replace the Oil Pressure Switch, because this always seems to go bad after having the Oil Control Valve replaced. I guess they were right and apparently they never changed the switch because they determined that this was the problem and confirmed that they had only replaced the Oil Control Valve the first time. They said the car was safe to drive and they had to order the part. After I left the dealer, I started having problems with the car acting like it was going to stall when stopped at traffic lights. I parked it and waited for the part to come in. Replace it myself in about 5 minutes (dealer wanted $200 labor). Reset the computer and still had the same problem. The next day, I tried to drive it to work and it died at a light and when slowing down to pull into a gas station just after this. Ended up that the car just needed the trottle plate cleaned of carbon residue. Seriously?!?!?! Oh, and of course they charged me $150 to do the cleaning! Anyways, the car is running great again... I hope this may help some of you other guys that are having similar issues. Good luck!!!

Yea yours is a 2.5i. They have a valve and a pressure switch.

 

2005 Turbos just have the OCV

Ahhh... good to know. Well, the throttle plate cleaning should still apply... right?

Maybe you guys can help me out.

 

My car is an 05 LGT. There is a stumble at idle and at heavy throttle. I bought the car last year, it had a burnt valve and the dealership rebuild both heads before I purchased it.

 

I plugged in my laptop and ran Romraider to log. #2 cylinder has roughness, usually maxing out around 10. No codes are showing. Cleaned the MAF sensor awhile ago. Car is stock aside from an AEM dryflow intake filter replacement. New battery and had the alternator rebuilt 2 weeks ago.

 

I just swapped coils between cylinder #2 and #3. Roughness stayed on cylinder #2, so I figure it's likely not the coils then.

 

What should I do next? Replace the spark plugs? I don't know if the dealer put new ones in when they rebuilt the heads. Otherwise, is the next likely cause the injector? I can swap those between cylinders to see if it moves.

 

Any help would be appreciated, this is frustrating. Aside from the stumble, the car runs well. Doesn't burn oil between changes, same gas mileage as it has always been.

Edited September 14, 2013 by Enraged

Post up a log. Where are you seeing the knock count increase? Light load? Heavy load? Part or full throttle?

 

I'm still trying to figure out why some people say the knock sum isn't something to fret about.

I'll try to get a log this weekend. Usually it's only noticable at idle and heavy load/full throttle. I haven't driven the car hard since it started, and if I feel a misfire I back off on the throttle. Driving around town is fine.

 

What should I log? Knock count/sum, roughness, anything else?

I know nothing about this but this is what I was told to log when trying to figure out what was wrong. Eventually the engine came out for new valves too!

 

Engine speed

Knock sum

Throttle opening %

Engine load

Feedback Knock Correction

Fine Learning Knock Correction

IAM

Ignition Total Timing

Manifold relative pressure

Primary Wastegate duty cycle

Boost error

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: stuttering from 2-3k, nearly every throttle position

 

MODS

Intake: Cobb short ram intake

Exhaust: Catless up-pipe, catted downpipe, catback

Engine: EJ257 Swap w/ CP pistons; 10k on build.

Fuel: stock

Turbo: stock

Engine Management: Cobb stage 2 map (OTS map w/intake)

Tuner and revision of tune(if you don't mind): n/a

 

MAINTENANCE

Sensors changed:knock sensor (no change)

Plugs changed: plugs changed; were very white from a lean condition. from leaking turbo inlet? (no change)

Coil Packs changed: n/a

 

OTHER SYMPTOMS

Check Engine Light: none

Etc: Found torn inlet, leaking bpv and tmic. Replaced inlet w/OEM, replaced bpv w/OEM, bulletproofed tmic which fixed the minor leak. pressure tested to 10psi with no leaks.

 

RESULTS

What has and hasn't worked for you: The torn inlet was a big problem, but stuttering still is present. Nothing has worked at this point. I am experiencing a lot of feedback knock at low throttle/low rpm which doesn't make sense. I have no knocking under WOT. I've check probably a half dozen times for something loose or bouncing around to cause the knock, but I haven't found anything.

 

If something worked, how long has it been working for: Nothing has worked at this point. I've been suggested to replaced my upstream o2 sensor regardless of having no codes; does that seem like a good idea? please help!

Filled my driveshaft hanger bushing with Windo-Weld Polyurethane. Significant improvement in surging issues and overall driveline slack.

 

Been meaning to do this for 5 years.

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: stuttering from 2-3k, nearly every throttle position

 

MODS

Intake: Cobb short ram intake

Exhaust: Catless up-pipe, catted downpipe, catback

Engine: EJ257 Swap w/ CP pistons; 10k on build.

Fuel: stock

Turbo: stock

Engine Management: Cobb stage 2 map (OTS map w/intake)

Tuner and revision of tune(if you don't mind): n/a

 

MAINTENANCE

Sensors changed:knock sensor (no change)

Plugs changed: plugs changed; were very white from a lean condition. from leaking turbo inlet? (no change)

Coil Packs changed: n/a

 

OTHER SYMPTOMS

Check Engine Light: none

Etc: Found torn inlet, leaking bpv and tmic. Replaced inlet w/OEM, replaced bpv w/OEM, bulletproofed tmic which fixed the minor leak. pressure tested to 10psi with no leaks.

 

RESULTS

What has and hasn't worked for you: The torn inlet was a big problem, but stuttering still is present. Nothing has worked at this point. I am experiencing a lot of feedback knock at low throttle/low rpm which doesn't make sense. I have no knocking under WOT. I've check probably a half dozen times for something loose or bouncing around to cause the knock, but I haven't found anything.

 

If something worked, how long has it been working for: Nothing has worked at this point. I've been suggested to replaced my upstream o2 sensor regardless of having no codes; does that seem like a good idea? please help!

 

Clean your throttle body. It worked for me.

 

Sent from my LG-E970 using Tapatalk 2

Filled my driveshaft hanger bushing with Windo-Weld Polyurethane. Significant improvement in surging issues and overall driveline slack.

 

Been meaning to do this for 5 years.

 

That is impressive, and one of the better pieces of ingenuity you've provided.

 

Wish I'd have thought of it. I used that poly to fill my '05's diff bushings, with a considerable improvement before there were "kits." I also used it to fill the rear LCA bushing, with similar improvements. I've used it elsewhere with success. But I never thought of that one.

I might go to town with that stuff and fill my whole car.

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: Pretty much at or just around 5,000 RPM exactly, at WOT, never happened outside this range and only happens in 3rd and 4th (its 5EAT) - but then not always (if it happens in 1st and 2nd, I don't feel it) Generally can reproduce it if I floor it from 1st and take it right up the rev range through all gears. Hit about 5,000rpm's in 3rd and its like someone's turned off the fuel line for a split second. Its an '07 LGT 5EAT

 

MODS

Intake: none

Exhaust: Catted DP

Fuel: 98 Octane (about US 95 equivalent)

Turbo: Stock (VF44 I think)

Engine Management: Stock ECU

Tuner and revision of tune(if you don't mind): Cryo, stage 2. Final revision.

 

MAINTENANCE

Sensors changed: Changed O2 sensor

Plugs changed: 10,000km's ago

Coil Packs changed: Not tried

 

OTHER SYMPTOMS

Check Engine Light: Never

Etc: Car runs perfectly otherwise

 

RESULTS

What has and hasn't worked for you:

O2 sensor replaced. That *seemed* to work for a while, but then came back straight after flashing an ECU revision. May have been coincidence. Reverting the revision did not sort it (although possibly cooked the O2 sensor again? Unlikely?) Its in getting a service right now and the auto electrician just rang said that their diagnostic tool showed a error code on the TCU - he reset it, in-case it caused an issue. Unsure what the error was, but I'll try driving again when I pick it up. I'm not confident that it will resolve though.

Edited November 21, 2013 by chimera

I remember catalyst had a very similar issue and it turned out to be his silicone intake collapsing at about 5200rpms causing a huge power surge like you describe.

 

The TCU thing is interesting based on what we were seeing with the weird rpm behavior during the pulls.

 

Dave

Update: I cleaned my throttle body and no improvement

Filled my driveshaft hanger bushing with Windo-Weld Polyurethane. Significant improvement in surging issues and overall driveline slack.

 

Been meaning to do this for 5 years.

 

good idea! have you noticed any increase in nvh? any pics?