2001 chevy cavalier code po303 how to fix it replaced the spark plugs how to fix it it has a rough idle, weak acceleration ce light starts flashing on acceleration and hard to start

To begin with, is your "check engine (CE)" light on? If it was on and now its not, you need to replace the bulb. If CE lights is on, find out the codes before doing anything. If bulb is good and "CE" does not come on, begin with: (1) gapping spark plugs, (2) replace spark plug wires (if haven't changed them within the last 2), then the coil. If your Cinco is still idles rough, adjust gas pedal until idling smoothly. If this still doesn't help, replace your two oxygen sensors. If still running rough, the converter. After doing all this and problem is still present, take it to a mechanic you trust.

I had the same problem on my 2001 Sunfire (same car as the Cavalier-different branding) which I was able to fix successfully.

My symptoms were:
-Traction Control OFF light illuminated
-Cooling fan running even if engine cold and it was freezing outside (I also noticed that when the Traction light illuminated, the fan would then begin)
-Rough idle with black smoke when cold
-Poor fuel economy


I have a code reader which produced codes P0130 and P0171. These are error codes for the upstream oxygen sensor (the one under the hood).

I simply replaced the O2 sensor (it took me 10 minutes). I did not reset the check engine light after the repair as I wanted to see what the car would do on its own. The idle was much smoother with no smoke and the cooling fan stopped running unnecessarily. After 1/2 mile down the road, the Trac light went away and the system functioned normally. I tested this by trying to accelerate quickly up a snowy driveway. I also noticed that the acceleration and shifting (auto tranny) were smoother. I reset the check engine light. All is satisfactory.


What was happening to the car before the repair:

P0130 is usually for a bad O2 sensor and P0171 is the sensor detected that the motor was running too lean (but it actually wasn't-the sensor was essentially giving a false lean signal).
The rough idle, black smoke, and poor economy are due to running too rich. In my case, the sensor told the PCM (the car's computer) that the air/fuel mixture was too lean. In response, the computer said "OK, more gas!" That's why it ran rich. This was evidenced on the old O2 sensor as well...it was completely caked with carbon from an excessively rich mixture. This further destroyed the performance of the O2 sensor.

i still have same code po303 i have change spark plugs and coil i add a ground wire i can resat end drive for 20+ milages no check enigine light
turn off start up runs for minute or so then coms back on check enigine light same po303 enigine runs very smoth no vibration what so ever I AM LOST

It is hardly ever the spark plug or only the spark plug - generally for some reason there is a weak or lost spark and the reason must be found and rectified by carefully checking and then replacing any components found to be edfective - plug wires, coil, distributor cap, rotor (if fitted), wiring, connections and could conceivably even be the ECU. Perhaps the misfire is due to injector trouble...

Sometimes a fault with persist even after it has been "cured" until the fault code is erased with diagnostic equipment.

Timing chain ,marks right ?

You may want to check the MAF, ( mass airflow sensor ), they are a very common problem with the issues you are having.

Do you know if the plugs were changed, a bad or broken plug will also cause rough idle and slow acceleration?

What engine? You need to have it scanned for codes. Autozone will do this for free

Have you made sure your getting spark on every cylinder from the coil pack?

I had a similar problem with an earlier model Cavalier, with the problem being much more pronounced. The fuel injector nozzles on two cylinders turned out to be the culprits. Once replaced, the car ran beautifully like it always had before.