Running Terrible! HELP!

im also having a werid problem with my 99 she has 256xxxx km i did loose one muffler ahile back a cpl weeks after i had started to notice a werid issue while climmbing a hill my tach jumps between 1500 and 2000rpm i give the car a little extra gas the problem goes away i do have an evap code showiing only wasnt sure if one muffler broke would cause it to go out of whack the car has been very good to me since i bought it since may using only supreme gas in the car just wondering if anyone had any theroys on this all the wiring looks good as well the car idles fine drives fine just has this issue on hills

^^^ To Falco: this could be the torque converter clutch slipping. Try locking out the gear in 2nd (shift into "2"). The car will only operate in 1st & 2nd gears, see if you can get the issue to repeat. If you can repeat, it's not the TC clutch. If you cannot, try the same test in gear "3", then in "OD". Let us know what happens.

so one muffler off altogether wouldnt cause this i spoke to a mechanic who said that it could be caused by the back pressure being thrown off also i shold have mentioned this when i floor it she shifts through all gears no problem including going uphill

No, the muffler shouldn't cause a fluctuating RPM, it just makes the exhaust sound louder.

When you floor the gas, the transmission doesn't use the torque converter clutch, so that would eliminate the issue under heavy throttle.

When the RPM changes going up hills, do you feel any pulsation from the drivetrain?

all i feel is the car bucking a little bit

See if you can get it to happen in 2nd gear. Try setting cruise control in 2nd while going up a steep hill.

then she shifts and goes on i was thinking about trying some lucas transmission fix

What does it mean "she shifts and goes on"?

Try to make the issue happen in 2nd gear. Put the shifter in 2nd and try climbing a hill.

Or try the Lucas and let us know how that goes (I don't think it will help your issue).

i mean she shifts and the problem goes away

If there's no problem in 2nd, see if you get the problem to happen in 3rd. You might need to apply cruise control at 45-70 k/h.

i tried what u said i couldnt see the problem anywhere i tried no matter the steepness of the hill except in od i was talking to a buddy of mine who has a monte carlo with the 3,8 as well dual mufflers he had the same problem as me his was caused by the baffles in the mufflers so he replaced them and the problem was gone so im thinking ill replace the muffler this week and see what happens also i do now have a check engine light i hooked it up to a scanner and it showed up evap code would that have anything to do with it i wonder?

My car ran really bad for awhile until I put in a new tranny modulator.made a world of difference.the OE was shot to shit,made the car behave like a fat toad

Try this - when the problem is happening, hold the gas pedal steady as you were, and touch the brake pedal just enough to put the rear brake lights on and hold it there. Don't step on the pedal enough to actually slow down the car or drag your brakes. Applying the brakes with disengage the torque converter clutch and if the problem goes away you have possibly found a big clue. The clue is that the torque converter clutch is causing the bucking. What you don't know is if the problem is actually the clutch, or if it's the solenoid.

I do not think replacing the muffler will have any effect on this problem.

Please put the year of your car, and if SC or NA in your signature and enable it, so we can help you better.

Was your friend's Monto Carlo supercharged? If not, the exhaust systems on these cars are not comparible. We have seen cars without ANY mufflers not having the problem you describe.

The EVAP code is likely unrelated to your RPM issue. Could be the purge valve, or something else related to the EVAP system, maybe the canister. More info on the EVAP codes:

https://rivperformance.editboard.com/t7197-p0441-1441-evap-emission-canister-purge-keeps-coming-back

When you say this only happens in OD and only at low RPM, it seems to be describing the TC clutch disengaging - as if it's slipping. If you have a scan tool that can show TCC lock-up and unlock, you can see the status of the clutch (on or off), and if it coincides with your issue. A transmission mechanic can provide this service for a small fee if you don't have the equipment.

robotennis61 wrote:

My car ran really bad for awhile until I put in a new tranny modulator.made a world of difference.the OE was shot to shit,made the car behave like a fat toad

Robo, he's got a '99 with the 4T65-E. I'm not sure if ours have the modulator?

PS - good tip from Derek about tapping the brake while on the gas.

...oh...

I don't know for sure, you might be right robo. Maybe someone will chime in.

i should have mentioned this part as well i put some injector cleaner into the car a cpl days ago and it seems like its not happening as often anymore i just put close to 80km on her since u made these suggestions to me as for the monte carlo yes it is supercharged same engine actually im wondering if dirty injectors or any part of the fuel delivery system may have been dirty and the cleaner worked it out