Hi there. I'm new here. I just purchased a 2000 S series sedan with a 4 banger.. It starts and runs good but now it shudders and hesitates when I press on the gas a little.
Sometimes it clears up,, but most of the time it happens. No knocking or timing rattle. It idles great . It does shudder a little in park when you barely touch the throttle. Fluids are all good and the oil is clean..
Could this be a clogged fuel filter? maybe a bad plug.. I live in a somewhat moist and windy town so maybe its condensation in the tank?
The air filter is good, so its breathing ok.. Hmmm,, any input would be great,

Thanks in advance..

 

I'd get a new set of plugs and wires and install them. They're cheap enough and since you just got it, you have no idea how long it's been since the last tune up. I'd also get a bottle of Techron fuel system cleaner or Berryman's B-12 and put that in the gas tank and drive it to see if there's any improvement.

 

1) Where does the needle on the temp gauge sit at operating temp?
2) Throttle body cleaning is in order. Again, you have no history on your new ride

If throttle body cleaning doesn't help:
3) WITH THE ENGINE COLD
Place a catch pan below the side of the engine block (driver) on which you are working.
Pull the ECTS squeeze connector, remove the ECTS from the head and have someone hold their finger over the hole to keep coolant in the system.
The exterior of the sensor should be all brass. If it has a resin tip, you've likely found your problem.
Please measure the resistance, noting the temp, and we will sort out.

If replacing ECTS, replace both ECTS and connector pigtail with parts obtained from a GM dealership; no generic autozoo crap if you want it to work right. S cars base a lot of decisions off the ECTS info......