Bad bucking and rough idle
Thread Starter
Junior Member
Joined: Nov 2010
Posts: 46
Likes: 0
From: Lancaster, PA
Car: 91 Camaro Z28
Engine: 305 V8 (5.0L) TPI
Transmission: 700R4
Axle/Gears: 2.73
Bad bucking and rough idle
*Car details :91 Z28 that is bone dry stock (exhaust and all) with the automatic TPI 305 with 140k on the clock.
Recently I have been having an issue with bucking after roughly 10-15 minutes of driving. It has stalled when bucking when changing from "drive" to "reverse". Luckily it just barely started enough to back it in my spot. It runs great then starts bucking after a little bit of driving then gets progressively worse if I keep going, the idle in "park" is extremely rough. If I shut the car down after it starts bucking it won't start and sounds like the car has absolutely no life at all. If I let the car sit for atleast 2 hours or long enough to cool down completely it starts up and would run like nothing is wrong for the rest of the day.
*Note: this happens atleast 1 to 3 times a week. When a whole week without the problem last week until friday. I noticed that if I don't really get on it at all and drive 100% civilized it doesn't act up as often. It doesn't buck when not on the accelerator. It has been showing me that the engine has been getting hot but not 100% sure if the gauge is accurate because my cluster is off and on on the speed o meter and 1/4 off on my gas gauge.
** My buddy and I were thinking a clogged cat or muffler. I ordered the Borla cat system for now and thats on its way. Hoping that will help. It has had a metal on metal sound coming from the exhaust but I hadn't had the $ to take care of it untill recently.
Any idea what is going on? Thanks for any help guys!
Recently I have been having an issue with bucking after roughly 10-15 minutes of driving. It has stalled when bucking when changing from "drive" to "reverse". Luckily it just barely started enough to back it in my spot. It runs great then starts bucking after a little bit of driving then gets progressively worse if I keep going, the idle in "park" is extremely rough. If I shut the car down after it starts bucking it won't start and sounds like the car has absolutely no life at all. If I let the car sit for atleast 2 hours or long enough to cool down completely it starts up and would run like nothing is wrong for the rest of the day.
*Note: this happens atleast 1 to 3 times a week. When a whole week without the problem last week until friday. I noticed that if I don't really get on it at all and drive 100% civilized it doesn't act up as often. It doesn't buck when not on the accelerator. It has been showing me that the engine has been getting hot but not 100% sure if the gauge is accurate because my cluster is off and on on the speed o meter and 1/4 off on my gas gauge.
** My buddy and I were thinking a clogged cat or muffler. I ordered the Borla cat system for now and thats on its way. Hoping that will help. It has had a metal on metal sound coming from the exhaust but I hadn't had the $ to take care of it untill recently.
Any idea what is going on? Thanks for any help guys!
Last edited by Mr. McGuire; Aug 4, 2013 at 10:14 AM. Reason: added more
Member
Joined: Aug 2013
Posts: 113
Likes: 1
Re: Bad bucking and rough idle
*Car details :91 Z28 that is bone dry stock (exhaust and all) with the automatic TPI 305 with 140k on the clock.
Recently I have been having an issue with bucking after roughly 10-15 minutes of driving. It has stalled when bucking when changing from "drive" to "reverse". Luckily it just barely started enough to back it in my spot. It runs great then starts bucking after a little bit of driving then gets progressively worse if I keep going, the idle in "park" is extremely rough. If I shut the car down after it starts bucking it won't start and sounds like the car has absolutely no life at all. If I let the car sit for atleast 2 hours or long enough to cool down completely it starts up and would run like nothing is wrong for the rest of the day.
*Note: this happens atleast 1 to 3 times a week. When a whole week without the problem last week until friday. I noticed that if I don't really get on it at all and drive 100% civilized it doesn't act up as often. It doesn't buck when not on the accelerator. It has been showing me that the engine has been getting hot but not 100% sure if the gauge is accurate because my cluster is off and on on the speed o meter and 1/4 off on my gas gauge.
** My buddy and I were thinking a clogged cat or muffler. I ordered the Borla cat system for now and thats on its way. Hoping that will help. It has had a metal on metal sound coming from the exhaust but I hadn't had the $ to take care of it untill recently.
Any idea what is going on? Thanks for any help guys!
Recently I have been having an issue with bucking after roughly 10-15 minutes of driving. It has stalled when bucking when changing from "drive" to "reverse". Luckily it just barely started enough to back it in my spot. It runs great then starts bucking after a little bit of driving then gets progressively worse if I keep going, the idle in "park" is extremely rough. If I shut the car down after it starts bucking it won't start and sounds like the car has absolutely no life at all. If I let the car sit for atleast 2 hours or long enough to cool down completely it starts up and would run like nothing is wrong for the rest of the day.
*Note: this happens atleast 1 to 3 times a week. When a whole week without the problem last week until friday. I noticed that if I don't really get on it at all and drive 100% civilized it doesn't act up as often. It doesn't buck when not on the accelerator. It has been showing me that the engine has been getting hot but not 100% sure if the gauge is accurate because my cluster is off and on on the speed o meter and 1/4 off on my gas gauge.
** My buddy and I were thinking a clogged cat or muffler. I ordered the Borla cat system for now and thats on its way. Hoping that will help. It has had a metal on metal sound coming from the exhaust but I hadn't had the $ to take care of it untill recently.
Any idea what is going on? Thanks for any help guys!
Have you pulled codes?
Do you get loping at idle?
Thread Starter
Junior Member
Joined: Nov 2010
Posts: 46
Likes: 0
From: Lancaster, PA
Car: 91 Camaro Z28
Engine: 305 V8 (5.0L) TPI
Transmission: 700R4
Axle/Gears: 2.73
Re: Bad bucking and rough idle
no didn't try hooking it up to the an OBD yet. very little bit of loping maybe. Possibly miss firing?
Member
Joined: Aug 2013
Posts: 113
Likes: 1
Re: Bad bucking and rough idle
Don't put on the new pipes until you know it's not defaulting to max injector pulsewidth. This will foul plugs, AND CATS, in short order.
I think you can get codes with a paper clip in the ALDL socket. Google for an image.
Loping idle is often a vacuum leak.
I think you can get codes with a paper clip in the ALDL socket. Google for an image.
Loping idle is often a vacuum leak.
Vacuum leak detection is hard to do right: I know of only one guy who did it right and found a leak (in IAC gasket):
Originally Posted by Schrade View Post
No one got the proper technique for vacuum leak detection...
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Bookmark this post YUP.
Wrench Wizard OUT!
No one got the proper technique for vacuum leak detection...
FIRST (fully warmed up motor); block the gas pedal, or block the throttle linkage. YOU HAVE TO DO THIS TO GET A STEADY IDLE , around 1,250 rpms, or a little higher. If you don't, you can fish starting fluid, a propane hose, or WD40, or Krylon, or hair spray, or pee, anything, until you need a sweater in Hades, but if the motor is lopin' idle already from a vacuum leak, you ain't gonna' find any leak, unless it's so big that Little Jack Horner can stick his thumb in it and pull out a pineapple NOPE.
AFTER you get a steady idle, THEN, you can spray starting fluid everywhere - that's the best detector, because it's vapor pressure is very high - a LITTLE at a time, all around the motor, until you get the rpm SURGE. Follow the vacuum lines to the EVAP cannister too. You might even have to follow the EVAP lines from the EVAP cannister to the gas tank too, but that vacuum leak will show up as a DTC 32 EGR fault, and won't normally show as loping idle, unless the EVAP cannister has been by-passed (been there, saw that uh-HUH yup).
If you get a surge in a tight spot, and can't tell exactly where it is, light a book of matches, blow out the match heads while they're still burnin', and feed the smoke to the tight spot to see it get drawn in.
Fear not the starting fluid; you cannot put the can down fast enough and light the matches fast enough to catch the starting fluid, because the vapor pressure is so high.
Bookmark this post YUP.
Wrench Wizard OUT!
Supreme Member
Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Re: Bad bucking and rough idle
When was the last time you did a COMPLETE ignition tune-up? Cap, rotor, plugs, wires AND A FRESH COIL.
Electronic components hate heat. They can sometimes exhibit problems that don't show up when they are cold.
The whole distributor could be in need of replacement in some cases. You can do it a piece at a time with a new module, pickup, condenser, etc. But it's often a pain in the rear to do all that and spend the same money as a whole new distributor.
Not saying this IS your problem, I'm just saying not to ignore the ignition side. It has driven me up a wall more than once on these cars.
Electronic components hate heat. They can sometimes exhibit problems that don't show up when they are cold.
The whole distributor could be in need of replacement in some cases. You can do it a piece at a time with a new module, pickup, condenser, etc. But it's often a pain in the rear to do all that and spend the same money as a whole new distributor.
Not saying this IS your problem, I'm just saying not to ignore the ignition side. It has driven me up a wall more than once on these cars.
Thread Starter
Junior Member
Joined: Nov 2010
Posts: 46
Likes: 0
From: Lancaster, PA
Car: 91 Camaro Z28
Engine: 305 V8 (5.0L) TPI
Transmission: 700R4
Axle/Gears: 2.73
Re: Bad bucking and rough idle
Well I had it looked at and turned out to be a bad distributor and wires causing a miss fire. Had a complete tune up done. The distributor rotor was rusted and stuck in place and had to hack some small plastic piece just to get the damn thing out.
Thanks guy for the help! Trending Topics
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