bad running buick century

[Guest]

buick century running real bad. car speeds up and slows down constantly while in park. could this be a sensor or egr valve?

[rtabish]

you might want to be a little more specific about the car. if it were a 55 century, i would say we were in trouble. even the newer fwd centurys can vary from year to year with what emissions controls, fuel delivery, and sensors are on which engines. it is all in the details.

[Guest]

the buick century is a 1994 model.

[tyesac]

Could be just a case of dirty sensors, like the mass air flow sensor, etc., OR, check the hose that feeds the PVC valve. If that hose is collapsing under different vacuum levels, the engine will have trouble maintaining steady idle speeds.

[NTX5467]

Idle speed is most probably being controlled by the Idle Air Control stepper motor. This is a spring loaded plunger that varies the air flow around the closed throttle plate in the throttle body assembly. It gets its commands from the ECM and it's various sensors. Does sound like it's trying to work, though.

EGR that has stuck or is prevented from closing fully at idle by deposit buildup under its plunger (pintle) will probably also cause missing at idle instead of just a varying idle speed.

Could also be an intake manifold issue or manifold gasket integrity issue. Could be deposits on the throttle plate or in the throttle bore preventing the throttle plate from closing fully (or as far as it needs to) at idle. Could even be a malfunctioning fuel injector.

The FIRST thing to do would be to pull the codes from the computer and see what they are! Otherwise, you can throw chunks of expensive parts at the car and still not have it fixed. Many of the auto supplies that will pull the codes "for free" are doing it so you will buy the parts from them--still no guarantee they will fix the car as some codes are inter-related. Similar with private/chain repair facilities that have a "simple" code scanner. You can also probably short two particular terminals on the ALDL connection to get the Check Engine Light to flash, but you'll need an ACCURATE list of codes for your particular year of vehicle to see what they are.

Getting the codes and dignositics and repair estimate from a quality repair facility or GM dealer would be the most expeditious way to get your Buick back to it's smooooooth running best. Then you'll have a much better picture of what the problem(s) are and what it will take to fix them successfully. These people will charge for their diagnostic time and expertise (as any professional should), but considsering that "time is money", it can be cheaper in the long run.

With computerized vehicle control systems, guessing can be conterproductive unless it's a clearly defined problem that is somewhat common. Unfortunately, as in other things, "No simple answers to complex questions". Vehicles aren't as simple as they used to be--and that's a whole 'nuther discussion.

This probably might not be the answer you were desiring, but that's the reality as I have observed it to be.

Happy Holidays!

NTX5467