Weird stumble when staying at same RPMs
Thread Starter
Instructor
Joined: Nov 2016
Posts: 118
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Weird stumble when staying at same RPMs
I have a 2000 manual vette and I noticed my car having a stumble when cruising at a certain RPM. It does this in any gear and it will continue to do it until I push the accelerator, then it accelerates normally but with a little hesitation. It does it with or without cruise, in town or on highway. I noticed it once and now it is more common. It feels like an unbalanced torque tube, obviously not but that is what I would compare the feeling too. The shifter moves up and down, sometimes pretty violently. I only have a code for an O2 sensor. Any help is appreciated. Thanks
Burning Brakes
Joined: Jan 2006
Posts: 788
Likes: 105
From: Olathe Kansas
Sounds like to me you have an engine that is not running perfectly.
Maybe time for some tlc
Plugs, Wires, Fuel Filter, Clean TB, Clean MAF, Clean or replace air filter
That's prob where you need to begin, esp if you don't know exactly when replaced last (or ever)
Maybe time for some tlc
Plugs, Wires, Fuel Filter, Clean TB, Clean MAF, Clean or replace air filter
That's prob where you need to begin, esp if you don't know exactly when replaced last (or ever)
Burning Brakes
Joined: Dec 2017
Posts: 755
Likes: 272
It sounds like a misfire to me, but if you’re getting significant engine/drivetrain movement from a misifire, I’d be sure to check the condition of your engine and transmission mounts. As mentioned above, I’d also go through the list of typical wear items (plugs, wires, air filter, MAF, etc) and make sure everything is in tip top shape.
Instructor
Joined: Nov 2009
Posts: 182
Likes: 19
From: Williamson County, Texas
I have a 2000 manual vette and I noticed my car having a stumble when cruising at a certain RPM. It does this in any gear and it will continue to do it until I push the accelerator, then it accelerates normally but with a little hesitation. It does it with or without cruise, in town or on highway. I noticed it once and now it is more common. It feels like an unbalanced torque tube, obviously not but that is what I would compare the feeling too. The shifter moves up and down, sometimes pretty violently. I only have a code for an O2 sensor. Any help is appreciated. Thanks
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,344
Likes: 3,936
From: Cape Coral, Florida
OK, well I doubt you have a scan tool but looking at fuel trims and O2 sensors would help immensely in an accurate diagnosis without spending a lot of unnecessary money...yes, it could be a bad O2 sensor (a lazy sensor in your case) but then again it can also be "open" or "short to ground" in the O2 sensor circuit, a clogged injector or injectors on bank 1...and just because you have an O2 sensor DTC doesn't ALWAYS mean it's an O2 issue...to rule out ignition (wires) you can mix some water and baking soda (to make it conductive) in a spray bottle and spray that on the ignition system, rev the engine and look for a "lightning show"....do it in a dark garage...good luck and let us know what you find !!
Last edited by C5 Diag; Jan 2, 2019 at 01:36 PM.
Thread Starter
Instructor
Joined: Nov 2016
Posts: 118
Likes: 0
OK, well I doubt you have a scan tool but looking at fuel trims and O2 sensors would help immensely in an accurate diagnosis without spending a lot of unnecessary money...yes, it could be a bad O2 sensor (a lazy sensor in your case) but then again it can also be "open" or "short to ground" in the O2 sensor circuit, a clogged injector or injectors on bank 1...and just because you have an O2 sensor DTC doesn't ALWAYS mean it's an O2 issue...to rule out ignition (wires) you can mix some water and baking soda (to make it conductive) in a spray bottle and spray that on the ignition system, rev the engine and look for a "lightning show"....do it in a dark garage...good luck and let us know what you find !!
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Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 327
From: CA.
St. Jude Donor '13-'14-'15
P1134 is for a fouled 02 FRONT sensor on the driver's side------The front 02's are very imprtant as they command all of your P/T fueling based on the data the front 02's show-----The rear 02's are only there to report the condition of your cats and have NO affect on how your engine runs
A bad front 02 sensor will flatline at .450 millivolts---As a safety once they flatline they will run pig rich rather than lean as a engine saftey They are just like sprak plugs once they foul they are junk !!!
PS IF you have LT headers and maybe even some shorty hdrs this is why they foul-
Especially with LT headers the front 02 locations are moved as much as 3 ft further back-----This makes them not heat up correctly and read in correctly-- That's why LT's are illegal in most states---Tuning helps but there is no 100% fix
If you have stock exhaust chances are you need new front 02's---Someone with a scannercan tell you if your 02s are dead or not They are cheap--just changes them--Make sure to clear the code after you change them !
A bad front 02 sensor will flatline at .450 millivolts---As a safety once they flatline they will run pig rich rather than lean as a engine saftey They are just like sprak plugs once they foul they are junk !!!
PS IF you have LT headers and maybe even some shorty hdrs this is why they foul-
Especially with LT headers the front 02 locations are moved as much as 3 ft further back-----This makes them not heat up correctly and read in correctly-- That's why LT's are illegal in most states---Tuning helps but there is no 100% fix
If you have stock exhaust chances are you need new front 02's---Someone with a scannercan tell you if your 02s are dead or not They are cheap--just changes them--Make sure to clear the code after you change them !
Thread Starter
Instructor
Joined: Nov 2016
Posts: 118
Likes: 0
P1134 is for a fouled 02 FRONT sensor on the driver's side------The front 02's are very imprtant as they command all of your P/T fueling based on the data the front 02's show-----The rear 02's are only there to report the condition of your cats and have NO affect on how your engine runs
A bad front 02 sensor will flatline at .450 millivolts---As a safety once they flatline they will run pig rich rather than lean as a engine saftey They are just like sprak plugs once they foul they are junk !!!
PS IF you have LT headers and maybe even some shorty hdrs this is why they foul-
Especially with LT headers the front 02 locations are moved as much as 3 ft further back-----This makes them not heat up correctly and read in correctly-- That's why LT's are illegal in most states---Tuning helps but there is no 100% fix
If you have stock exhaust chances are you need new front 02's---Someone with a scannercan tell you if your 02s are dead or not They are cheap--just changes them--Make sure to clear the code after you change them !
A bad front 02 sensor will flatline at .450 millivolts---As a safety once they flatline they will run pig rich rather than lean as a engine saftey They are just like sprak plugs once they foul they are junk !!!
PS IF you have LT headers and maybe even some shorty hdrs this is why they foul-
Especially with LT headers the front 02 locations are moved as much as 3 ft further back-----This makes them not heat up correctly and read in correctly-- That's why LT's are illegal in most states---Tuning helps but there is no 100% fix
If you have stock exhaust chances are you need new front 02's---Someone with a scannercan tell you if your 02s are dead or not They are cheap--just changes them--Make sure to clear the code after you change them !
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
If you have a code for o2 sensor, then it's pretty much guaranteed that you're running way out of tune. It's possible that swapping plugs temporarily cleared it up by getting rid of a fouled one (due to running out of tune). But definitely get those new sensors in there ASAP. They're very easy to replace.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 327
From: CA.
St. Jude Donor '13-'14-'15
Also the side with the failing 02 sensor will create an imbalance of fueling between the left and right banks As the side with the good 02 is self correcting the AFR ratio to stoich during part throttle but the side with the bad 02 is confused and making ridiculous adjustments !!!! Saying that it clears up when you floor the throttle confirms this --As when you go into power enrichment and floor the throttle the front 02's are turned OFF and NOT used for fueling at all --- so there is no imbalance between L/R as during P/T---
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Also the side with the failing 02 sensor will create an imbalance of fueling between the left and right banks As the side with the good 02 is self correcting the AFR ratio to stoich during part throttle but the side with the bad 02 is confused and making ridiculous adjustments !!!! Saying that it clears up when you floor the throttle confirms this --As when you go into power enrichment and floor the throttle the front 02's are turned OFF and NOT used for fueling at all --- so there is no imbalance between L/R as during P/T---
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 327
From: CA.
St. Jude Donor '13-'14-'15
A vacuum leak WILL affect WOT fueling !! As it is Un METERED AIR that the MAF is not reading and then there is no fuel compensation to correct it during PE ----It will as well make your fuel trims work very hard and go crazy to try and correct the AFRs at PT
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
not that I've ... ever done that
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 327
From: CA.
St. Jude Donor '13-'14-'15
Uhh, no, all air is un-metered at WOT as the MAF signal essentially gets ignored. Try it for yourself if you don't believe me. Leave the air bridge loose enough that you can barely idle then go for a drive. Once you floor it, everything is perfect again.
not that I've ... ever done that
not that I've ... ever done that
YES you can trick your ECM by commanding a richer AFR to get an actual AFR at WOT but that is NOT ideal for perfect tuning Ideally you want the commanded AFR to match your actual AFR with the wideband------The MAF reading is used only during "rapid changes in airflow" as a back-up referance--so if the un metered air is not being recorded you will get erroneous MAF back-up corrections at WOT or PE--- Unmetered ir is always bad theECM does not seperate from P/T and WOT fueing dues to a vacuum leak---
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,344
Likes: 3,936
From: Cape Coral, Florida
Uhh, no, all air is un-metered at WOT as the MAF signal essentially gets ignored. Try it for yourself if you don't believe me. Leave the air bridge loose enough that you can barely idle then go for a drive. Once you floor it, everything is perfect again.
not that I've ... ever done that
not that I've ... ever done that