2003 chevy malibu rough idle

SOURCE: 2002 chevy trailblazer has rough idle

it could be an o2 sensor. it could also just need a tune up

SOURCE: 2003 Silverado rough idle, idles good after "check engine" light

Check your o2 sensor voltage, those trucks are real bad for o2 sensors, and yes if one sensor is reading 0mv, the others will start to drop out, and the vehicle will run very, rough. You also may check fuel system pressure, should be almost 60p.s.i. If its alot lower, Id be looking into a fuel pump. If that vehicle is drive-by-wire (no throttle cable), the throttle bodies get very dirty and cause that concern also. Id start by having the vehicle scantested.

Marvin

• 85242 Answers
• Posted on Apr 14, 2009

SOURCE: IDLE PROBLEM

Here are some of the causes of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

SOURCE: Engine misfire, EGR replaced still rough idle!

First, check the passageway to the egr valve to make sure it is clear (often plugs up with carbon) second, make sure that the egr control is working. Also a good idea to have any codes checked and old ones cleared.Computer may need to cycle a few times to "learn"new parameters.
In general, it is good to shut down your engine when check engine light comes on...The next step after that is to determine why the light came on.
If the cause is an oil related or coolant related item, you should drive no further 'till it's corrected...However, there are numerous sensors that can turn it on with no disasterous results if you continue to drive One example is the light coming on because a gas cap has not been put on correctly...On many vehicles this will turn on the light and set a code, but the car will suffer no damage if you drove to your destination before correcting it.So, if the light comes on and it is not overheating and you have good oil pressure, and you hear no noises from engine, have it looked at but don't put yourself in danger on the side of a major highway for a nonsense code.
Most major parts houses will read codes free...take advantage of that service and get yourself a basic repair manual, so you have an idea what all the stuff under your hood is and does.
Good luck with your car!!

SOURCE: rough idle on 1999 chevy cavalier z24

Check for vacuum leaks. Spray some carb cleaner or WD40 around the intake manifold, trottle body and any vacuum lines. Check for loose connections on engine wiring harness (Maybe you disconnected a sensor, and forgot to re-attach it?).