Help... Car jumps under acceleration

**3R1CD4V15** · 05-03-2012

My 1997 gtp with 156k miles has started to "jump" under acceleration sometimes.
Started yesterday when I was going up a long hill, I was crusing at about 1600rpm or so and I gave it a little gas to maintain the same speed, then it started "jumping". So I gave it more gas and it down shifted and no more problem.

Now today I took it out and it did it a little bit under normal acceleration in first gear, then 15 mins later in 3rd or 4th gear.
It dosent do it all the time, its actually kinda hard for me to get it to happen.
But it seems to do it at lower rpms.
When it did happen I didnt see the tach move at all. No rpm drop.

Idle is fine, except when I start it after Ive been driveing it for a while, It will idle low (600 rpm) and I give it a little gas and no issue.
I can also hear a "poping" in my exhaust crusing at 55mph. Sounds like a slight backfire or somthing?

SES light has been on for a month or 2, I ran the codes back then and it said O2 senors were bad. (never fixed it tho)
Havent ran the codes recently.

Tried looking up this problem and these are thing I think I should check:
Fuel filter
maf
iac
knock sensor
o2 sensors

Any help would be much appreciated.

Thanks,
Eric

**EJOUIE** · 05-03-2012

I would fix the o2 so that you can clear that code because there are probably some new codes set in there as well.

**tayl5645** · 05-03-2012

If the rear O2 are reading bad it could be a cat issue but usually you would see that at higher RPM. Ive seen the issue before however, rear O2s shouldn't change livability at all they are meant purely as a diagnostic tool. DO you have the exact code? Cause if its the front O2 you should especially replace that as the fuel trim is set by that and you really dont want to be running excessively rich or lean because the O2 is reading incorrect.

**BillBoost37** · 05-03-2012

Fix the known issues. A bad (upstream) o2 can lead to a bad catalytic and that leads to an empty wallet and a bad running car.

Likely it's tune up related (plugs, wires, etc) and or O2 etc.

**3R1CD4V15** · 05-03-2012

Ran codes again:

P0300- Random multiple misfire detected

P0420- catalyst sytem efficiency below threshold (book says this is probly the converter plugged)

would the 420 cause the 300 code?

**Rico** · 05-03-2012

So the O2 sensor code is gone?

A clogged catalytic converter can cause P0300 random misfire.
At 150K I would just replace the cat and never look back.
Clear codes and see what happens.