new car issue

[pass1over]

car started having some drivability issues a few weeks ago. The engine will jerk and buck like its missing or the air/fuel mix is wrong. It does it more under light load, light acceleration situations, but it also does it at WOT as well. It's intermittent, sometimes it pulls normally and light acceleration in traffic is normal as well. Other times, it's definitely not a happy motor.

I changed the plugs, because it was time anyways. That made no difference. Doesn't matter if it's 1/4 tank of fuel or full tank of fuel, so I don't think it's a fuel pump issue. Maybe a coil pack is going bad, but not enough to trigger a misfire? There are no CELs on, nothing to indicate anything is wrong.

two other things I noticed this morning on the drive in to work. My head unit plugs into OBD2 port and I have data on the screen.
1. coolant temp is staying around 180, this seems a little low?
2. it shows accelerator pedal position as a %. When pedal is at rest (foot not on it), it shows 15% pedal activation, at WOT, pedal on the floor, it only goes to 84%. Is this measurement taken from the TPS? Seems like it should be 0% and 100%, no?

 

[Dino Dino Bambino]

The coolant temp. should be in the 192-201*F range if you have a stock 192* thermostat. It would appear that a PO installed a 180* thermostat, though that lower temp. wouldn't cause any problems.

A TPS of ~15% at idle and ~85% at WOT is normal, and there doesn't appear to be any conflict between the outputs of the APP (accelerator pedal position) sensor and the TPS.

The drivability problems you're experiencing could be from something as simple as partially clogged injectors or dirt in the fuel system. I suggest you add a bottle of fuel system cleaner (Wynn's works well for me) to your next tank of gas and let it get to work. I had a similar problem about two years ago and the stuff did wonders. Indeed I make a point of treating the fuel once/year with it to keep the system clean.

 

[GriffX]

The thermostat is 190 or 192, when I remember.

There are several PIDs for the pedal and TPS, depends what kind of OBD reader you have. etc_throttle_pos has 5 at idle, pedal_position 0

 

[pass1over]

The coolant temp. should be in the 192-201*F range if you have a stock 192* thermostat. It would appear that a PO installed a 180* thermostat, though that lower temp. wouldn't cause any problems.

A TPS of ~15% at idle and ~85% at WOT is normal, and there doesn't appear to be any conflict between the outputs of the APP (accelerator pedal position) sensor and the TPS.

The drivability problems you're experiencing could be from something as simple as partially clogged injectors or dirt in the fuel system. I suggest you add a bottle of fuel system cleaner (Wynn's works well for me) to your next tank of gas and let it get to work. I had a similar problem about two years ago and the stuff did wonders. Indeed I make a point of treating the fuel once/year with it to keep the system clean.

I'm the original owner, bought it new off the lot. I did not change to a lower temp thermostat, it's the original one in there I believe. I wouldn't put a lower temp thermostat in my car. Guess i'll get a new one though, swap it out.

I'll try the fuel system cleaner. A friend also suggested running a bottle of seafoam through it.

 

[pass1over]

upon further research, stock GT thermostat is 180, V6's got a 197

 

[Juice]

Sounds like it's going to throw the CEL soon, and you should have codes to help.
In the meantime, if you can read pending codes, you don't have to wait for the issue to mature.

 

[pass1over]

thank you for reminding me to check pending codes.

P2197 bank 2 sensor 1 stuck lean

going to swap o2 sensors and see if it follows or not

 

[DieHarder]

car started having some drivability issues a few weeks ago. The engine will jerk and buck like its missing or the air/fuel mix is wrong. It does it more under light load, light acceleration situations, but it also does it at WOT as well. It's intermittent, sometimes it pulls normally and light acceleration in traffic is normal as well. Other times, it's definitely not a happy motor.

I changed the plugs, because it was time anyways. That made no difference. Doesn't matter if it's 1/4 tank of fuel or full tank of fuel, so I don't think it's a fuel pump issue. Maybe a coil pack is going bad, but not enough to trigger a misfire? There are no CELs on, nothing to indicate anything is wrong.

two other things I noticed this morning on the drive in to work. My head unit plugs into OBD2 port and I have data on the screen.
1. coolant temp is staying around 180, this seems a little low?
2. it shows accelerator pedal position as a %. When pedal is at rest (foot not on it), it shows 15% pedal activation, at WOT, pedal on the floor, it only goes to 84%. Is this measurement taken from the TPS? Seems like it should be 0% and 100%, no?

Not that this is your problem but may be a possibility. Another member and I had the same problem at almost the same time which exhibited symptoms as you describe. Turned out a couple of COPS were bad (specifically the ends of the coils for the COPS) had retracted too far so they were not seating all the way down on the top of the plugs which led to missing/ bucking/ jerking/ bogging under load. If you kept your foot out of it you could drive her but she would complain if you tried anything beyond 25-30% acceleration. Turned out COPs 2&3 were causing the issue. Unfortunately, took a scan by a dealer to find it which cost me $200 but which I consider well spent (instead of firing off the parts canon) since I had just replaced all of the COPS a year before.

Word of Caution. Don't waste your time asking a dealer to replace them for you. They wanted an additional $800 to replace just two of mine. I actually thought the service person was joking with me when she gave me the quote. Nope, she was serious. When I asked Why she said the technician would verify that was the problem after replacing them... WTFO; Really? Word to the wise.... A set of stock OEM COPS can be had on Feebay for as little as $8 - 15 per COP... at least the last time I bought a set just a few months ago. Bought all 8 and replaced just two of them in about 10 mins (and I work slow).
Result: She's back to normal and running fine.

 

[pass1over]

wow, that's a lot of money to replace the COPs.

Turned out to be a bad upstream o2 sensor. I swapped it to bank 1 last night and the code followed.