Stumble at cruise only

After reading dozens upon dozens of threads on here about various forms of stumbling our cars seem to do I'm going to replace my front o2 sensor and here's my reasoning and description of my trouble.

 

Car runs good. Good power, good acceleration. Slightly rough idle and definite stumbling at cruise speed. This is most noticeable on the highway once the torque converter locks up. It is VERY annoying. It will hold it's speed fine. If I accelerate light enough that the torque converter stays locked I can clearly feel it stumbling as it picks up speed. If I push the pedal far enough to unlock the torque converter it feels fine but at this point I'm pretty into boost and the stumble only seems to happen around cruising levels.

 

I'm going to replace it because

 

#1 The car has 109k miles and looks original. I feel it's worth replacing even if I weren't having any issues with the way the car drives.

 

#2 I believe that it's probably very slow to respond and that is what is causing the feeling of rich/lean/rich/lean/rich/lean at cruise.

 

I will post my results here in a few days. The o2 sensor is supposed to be delivered on the 26th and I will know for sure that evening after I install it and drive the car on the highway.

Haveing similar experiance now but have changed the O2 sensor a fews miles ago. Not saying don't change it... did you go OEM or AM?

 

I'm puzzled and checking as I go for somthing missed. Almost like there is a vac leak but it's only at speed that I'm feeling it and between 2K and 3K.

Check your coils for the harness plugs being slightly loose. If you remove the coil packs and use needlenose pliers and slightly twist the pins inside, and then a tiny bit of dielectric grease on the female side on the harness plugs, you may fix your problem.

The harness plugs have been shown to become a bit loose on the coils and twisting them gives back good connection.

I chased a cylinder 3 misfire for about a week and once I did this, it completely went away, so I did it to all 4 just to make sure. You can feel the plugs being slightly loose by the way the pop off too easily when you release the clip.

Give it a try. Doesn't cost anything except a little time and generally, it's been known to fix those annoying stumble/miss/idle issues.

^ going to try this later today and also considering a injector cleaning/service.

Berryman Chemtool B12-put it in at 1/2 tank, drive it to 1/4 tank, and then refill with good gas (Mobil has the best cleaners) and drive it some more. This will generally help with injector and can, in a lot of cases, eliminate the problems.

 

Great stuff. Available at Autozone for about $4.50 or so.

UGN I wish I had known about the coil pack connectors, I just got done replacing all the plugs a few days ago. That's my luck.

 

I got the o2 sensor today, OEM denso. I don't have my car at home tonight but should have it back tomorrow and will install it.

Mine does the same! Very annoying. I changed plugs and went to my buddy to try to tune it out.. still have the problem.

New o2 sensor. No change. Logged on the highway when it's stumbling. I couldn't see any issues on the logs.

 

A slight revision to my symptoms. When logging I did notice it seems to do it right when you cross from vacuum to boost so it's doing it under slight loads, enough load to go into light boost.........

 

If that helps at all.

 

I will pull all my coils again soon, clean / twist the pins for a more solid connection.

Check for vacuum/ boost leaks commonly around the intercooler to Tb connection.

Could have a cracked vacuum hose. Can you do a boost leak test ?

 

I used a pint size paint can to plug the air inlet hose off the air filter box, then pulled the small hose of the blow off valve and gave it a quick blast of air from my compressor. Put my thumb over the hose and listen for leaks.

I have a very similar problem but also have a low idle in R and D. 5EAT.

 

I'm focusing on ocvs and injectors right now. Injectors are getting three rounds of injector cleaner. If that doesn't resolve it I know the OCVs get replaced for low idle, rough idle or stumbles.

Rob-2: I have the exact same car and setup as you, at Stage 2 and have had it that way for the last 7 years AND without a problem... until the last 3-4 months when I also got hit with the same stumbling as everyone else.

 

I'm on trip 6 to the auto shop (today was the most recent)... Trips 1-4, all the other shops gave up.

 

Like you, today I gave them a list based on forum most likelies and things to replace first. The o2 sensor was at the top of my list.

 

Instead however, for me, they looked at and replaced my now 7 year old Go Fast Bits blow off valve. The power difference is huge and the stumbling is completely gone. I had provided them a datalog from my Accessport which clearly showed my car dying twice.

 

The Cobb BOV set to full recirc did the trick. As a Subie tuner shop, they said the LGT is super sensitive to the BOV and cleaning can help but in my case, it was just time for a new one.

Rob-2: I have the exact same car and setup as you, at Stage 2 and have had it that way for the last 7 years AND without a problem... until the last 3-4 months when I also got hit with the same stumbling as everyone else.

 

I'm on trip 6 to the auto shop (today was the most recent)... Trips 1-4, all the other shops gave up.

 

Like you, today I gave them a list based on forum most likelies and things to replace first. The o2 sensor was at the top of my list.

 

Instead however, for me, they looked at and replaced my now 7 year old Go Fast Bits blow off valve. The power difference is huge and the stumbling is completely gone. I had provided them a datalog from my Accessport which clearly showed my car dying twice.

 

The Cobb BOV set to full recirc did the trick. As a Subie tuner shop, they said the LGT is super sensitive to the BOV and cleaning can help but in my case, it was just time for a new one.

 

Good information. I doubt if many people, myself included, would have looked at that as being the cause of the stumbling.

For clarity sake what RPM and gear are you guys feeling this particular stumble? Just want to be sure were alll talking apples to apples.

 

Mine is in 5th under load between 2K and 3K.

 

Have some plugs to change and some ATF to dump. Dielectric grease at the ready and will confirm the harness pins are clean and ready.

 

Already cleaned the PCV and checking if I have a head gasket failure. Seems I don't have a head gasket failure so thats a positive sign.

 

PCV cleaning did help idle some more so again good things comming out of the work done.

 

One item noting is Max mentioing a simple way of checking for vac leaks. Although I don't feel I have any it's worth a shot.

 

Cap the intake at the air box with a quaret paint jar and blow compressed air into the BOV vac line. Listen for leaks. Be great to add smoke to this mix too if I can.

 

Course now hunting for a front diff leak. It's either the passenger diff seal or the drain seal.

Rob-2: I have the exact same car and setup as you, at Stage 2 and have had it that way for the last 7 years AND without a problem... until the last 3-4 months when I also got hit with the same stumbling as everyone else.

 

I'm on trip 6 to the auto shop (today was the most recent)... Trips 1-4, all the other shops gave up.

 

Like you, today I gave them a list based on forum most likelies and things to replace first. The o2 sensor was at the top of my list.

 

Instead however, for me, they looked at and replaced my now 7 year old Go Fast Bits blow off valve. The power difference is huge and the stumbling is completely gone. I had provided them a datalog from my Accessport which clearly showed my car dying twice.

 

The Cobb BOV set to full recirc did the trick. As a Subie tuner shop, they said the LGT is super sensitive to the BOV and cleaning can help but in my case, it was just time for a new one.

 

Good info. Does anyone know the stock part number for the subi BOV? I think it's actually just a by pass valve.

Electronic Throttle Body+SI-Drive= Stumbley throttle pedal.

Stumble between 2K and 3K still present after plug change. Hoping the tuning gods will align and narrow this down with me.

 

Broke a locking clip on the harness connecting the passenger rear coil. Pissed but figured there has to be a way to swap these retainers.

Well see about that.

 

ATF looked used but nowhere near the first time I dropped the pan.

Intend to change another pan again during next IC in 800 miles or so.

Well see how that settles the transmission for a bit more.

Stumble between 2K and 3K still present after plug change. Hoping the tuning gods will align and narrow this down with me.

 

Broke a locking clip on the harness connecting the passenger rear coil. Pissed but figured there has to be a way to swap these retainers.

Well see about that.

 

ATF looked used but nowhere near the first time I dropped the pan.

Intend to change another pan again during next IC in 800 miles or so.

Well see how that settles the transmission for a bit more.

 

Just lock tight it in place.

Yeah, could be an option. Working well so far and going to look into replacemnt options. I'll snag some out of pick n parts if I have to but would rather have some new plastic to heat cycle.

 

Now one thing I want to report back is the plug change is still possibly helping. I havn't driven enough to make a clear determination if they smoothed out my situation.

 

After confirming I have the ATF at the right level after taking my daughter to school. I ran some additional test hits and in town driving... Not hiccupping as much at all after and idle is way smoother.

 

Curious how it goes tomarrow.

 

Will be driving into the office so a good 110 mile round trip should settle anything else the ECU needs to learn about it's new plugs.

Yeah, could be an option. Working well so far and going to look into replacemnt options. I'll snag some out of pick n parts if I have to but would rather have some new plastic to heat cycle.

 

Now one thing I want to report back is the plug change is still possibly helping. I havn't driven enough to make a clear determination if they smoothed out my situation.

 

After confirming I have the ATF at the right level after taking my daughter to school. I ran some additional test hits and in town driving... Not hiccupping as much at all after and idle is way smoother.

 

Curious how it goes tomarrow.

 

Will be driving into the office so a good 110 mile round trip should settle anything else the ECU needs to learn about it's new plugs.

 

I'm on brand new plugs and still have the problem. I'm wonder how old your plugs would have to be to cause this problem?

 

For me it feels more like a misfire or very faint lugging.

Almost inclined to say it's winter fuel. Depending on the source there is more methanol added.

 

Since thinking fuel now with the new plugs I'm going to fill back up at Chevron after the Arco is down to a quarter tank.

 

Added a can of the B12 in for the drive since I'm in use fuel mode and refill.

Almost inclined to say it's winter fuel. Depending on the source there is more methanol added.

 

Since thinking fuel now with the new plugs I'm going to fill back up at Chevron after the Arco is down to a quarter tank.

 

Added a can of the B12 in for the drive since I'm in use fuel mode and refill.

Let me know how that goes. I tried all of that already

 

FYI winter fuel doesn't change the knock rating or much sizable.

Yeah but additives differ greatly based on the distributor especially in this state with weak oxegenated gas to start with.

Yeah but additives differ greatly based on the distributor especially in this state with weak oxegenated gas to start with.

 

Arizona, California and Nevada share the same gas. You'd probably be surprised when winter gas actually goes on sale.

I had this issue. Turned out I just needed to flush the transmission. After the mechanic mentioned it could be the torque converter I remembered my mountain run a few seasons back and how the car never felt right afterwards. The ATF had broken down and the converter was having trouble. She feels back alive again now.