Out of nowhere this started just yesterday. The car idles fine and accelerates fine but once you get to a speed when you try to just maintain it the car starts jerking violently back and forth. It seems to kind of emanate from the rear of the car. It's not throwing and codes or anything. For instance driving along once I hit 40-45 mph trying to just maintain that speed in 4th gear the car starts violently lurching forward and back. RPM's seem constant when it does this and the exhaust sounds a little more erratic and/or bubbly.

It's not throwing and codes which makes it even more bizarre. It's bad enough that I'm not going to drive the car tomorrow its just to erratic and difficult to control and I can't keep speeding up/slowing down to keep it from doing that or riding around in 3rd gear at 50mph.

I also did a quick all around visual inspection there do not appear to be any leaks in the engine area, from the tranny area or coming from the rear diff and it doesn't leave any fluids on the ground when parked.

Recently had a new clutch put in by EnglandGreen with new hydraulics so I wouldn't think it would be in the tranny. The rear seals were also replaced at that time. But I don't know why my rear would develop trouble as it still has never been raced or put through any kind of abusive situation just daily driving.


Any ideas?


*** Update from later that day ***

Well that was weird. Decided to take it out to try and get a video of it to help explain it a little better. But it didn't do it just drove like normal. I dropped it down to 5th @ 40mph and it just chugged along. 6th gear @ 40mph and it let out a backfire. Backfired about 4 times while driving when dropping into 6th where rpms would be around 1100 and once just randomly pulling it out of gear and coming to a stop.

In any case it seems there may be a problem beginning to develop with this added information what do you guys think? plugs/wires? fuel pressure/pump?

I'm still just very surprised it didn't throw any sort of code I'd think bad wires and you'd get a code for a misfire or similar and a fuel problem I'd think you'd get a code about low fuel pressure. Thats the thing that really perplexes me these days cars have so many sensors that can at least point you in the general direction of the problem but I'm getting nothing.


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almost sounds like some sort of engine hesitation.. strange that it's only during cruise though..

 

Yea thats what makes it so weird when just applying normal acceleration through 1st, 2nd and 3rd and into 4th you wouldn't think anything was wrong then within 20-30 seconds of sitting in gear just maintaining speed it starts this violent jerking back and forth.

 

Are you running stock OEM sized tires? Almost sounds like traction control is being invoked.

 

I can't say for sure but I had a similar problem on my friebird. It was a plug wire that went bad. I would assume a code would be put up but not sure. worth checking though.

 

Yep stock sized and its been running fine no sudden changes.

 

possibly a bad plug wire(s) or plug(s)

 

Sounds like a miss in the plugs,wires. I had a camaro that did that. new plugs new wires new attitude

 

low fuel pressure. need to check...

 

Well that was weird. Decided to take it out to try and get a video of it to help explain it a little better. But it didn't do it just drove like normal. I dropped it down to 5th @ 40mph and it just chugged along. 6th gear @ 40mph and it let out a backfire. Backfired about 4 times while driving when dropping into 6th where rpms would be around 1100 and once just randomly pulling it out of gear and coming to a stop.

In any case it seems there may be a problem beginning to develop with this added information what do you guys think? plugs/wires? fuel pressure/pump?

I'm still just very surprised it didn't throw any sort of code I'd think bad wires and you'd get a code for a misfire or similar and a fuel problem I'd think you'd get a code about low fuel pressure. Thats the thing that really perplexes me these days cars have so many sensors that can at least point you in the general direction of the problem but I'm getting nothing.

 

Have you checked for history codes? I have had mid 80's GM cars do this and it was always tracked to the TPS, not sure how that relates to the Vette, sorry.

 

It started again on my way back from school. I filled up with Mobil gas and I think I'll drop a can of seafoam in the gas tank just in case it was bad gas or something.

Also when this happens the instant gas mileage goes way down about 10-15mpg lower then it would normally report for that speed. And again we're talking about maintaining a speed on a level surface so its not under acceleration.

 

Any updates on this?

 

It sounds just like my wife's Trailblazer...
Simultaneous rich and lean codes...
Diagnosis plugged catalytic converter...
Doing the replacement this week.

 

Hi there,
How many miles are on this vette?
If you had bad or loose coil,plugs or wires the DIC would display P0300.Multiple cylinder misfires.Any codes being displayed?
Backfiring usually means the timing is retarded or water in the gas. I would add a couple of bottles of dry gas to the tank. Buy the type that does not contain methanol as the c5 has plastic fuel lines.
If your mileage is about 80k I would be looking at a dirty or clogged fuel filter or a malfuncting fuel pump. Just out of curioscity I would be looking at the level of the tranny fluid since the car was not experiencing problems before.If you have a telescoping magnet that fits in the opening clean it off & insert.( looking for metal inside.)
robsc501

 

That sounds like a transmission seeking gears. Just as if you hit the sweet spot between overdrive and regular drive. I remember hearing a guy explain it to a mechanic once and he said that it only did it when he held the speed at exactly 34Mph.

The mechanic told him to drive at either 33 or 35Mph. Of course that didn't solve the problem but I thought it was a funny response coming from a mechanic.

 

Check of a cracked ceramic on a plug. Neighbor recently had the same problem.

 

...

 

Try keeping both hands on the wheel, this should stop the hard jerking.

 

How big is your cam, and when was it tuned, if at all? Does this happen at low cruising RPMs but subside at higher rpms? Sounds like it could just be a tunning issue.