Saturn Aura with rough engine idle

   I have a  2009 Saturn Aura, 4 cylinder, automatic transmission with 50,000 highway miles.  Sometimes intermittently and sometimes all day long the engine will miss and has a rough idle.  This can happen while waiting for a light, accelerating from a stop or while driving at speed on the highway.  Weather does not seem to be a factor.  Only once the engine was hard to start and ran very rough.  That is the only time over the past several months while experiencing this issue that a code was recorded in the computer. "misfire cylinder # 1" .  The spark plugs were replaced and the #1 fuel injector was replaced.  The misfire went away and returned.  The number 1 and 4 coils were swapped and the misfire continues but no code appears in the computer to indicate which cylinder has the problem.  I'd like to clear up the misfire, but also wonder why when the engine runs as rough as it does at times a code doesn't occur?  Any help would be appreciated.  By the way I believe my mechanic is topnotch and this is driving him nuts.  Thanks.

Has your mechanic checked the engine’s compression? This is a must for any misfire problem, and should be the very next thing (should have been done already). If it was or is done, post the actual numbers in psi.

You can probably find out if the misfire went with the coil by unplugging the spark plugs one by one while the engine is idling roughly (but do not just grab them with your hands! High voltage!) The ones that are working will make even more of a mess of the idle when you unplug them. The one that isn’t working won’t result in much of a change.

Your mechanic should be able to do something like a balance test on the injectors to find out if something is going on there.

A vacuum gauge will tell you in a few minutes whether there is reason to suspect a vacuum leak. In any case, a search for vacuum leaks should ensue. The same with a check of the fuel pressure.

Has the MAF sensor been cleaned?

Turned out to be a broken wire at the connector for the number 1 cylinder fuel injector. This time a code was recorded in the computer. “number 1 cylinder fuel injection circuit open”. Great that it is now running fine, but I’m still curious as to why the engine could run as rough as it did at times and no code recorded by the computer. Thoughts?

The computers are all programmed to tolerate a certain amount of misbehavior from anything they monitor. If they weren’t the dumb light would be going off all the time. I have often thought that the computers do tolerate too much misbehavior. This case is one of those. I have sometimes driven around for a week or so knowing something was off & waiting for the computer to “tell” me about it.

Thanks for coming back to give a follow up.

Cig roller & 6327: thank goodness that I stumbled upon this. Our son’s 4 cyl. '09 Aura has a very similar problem. His code reads “SERVICE ESC”. I noticed that the unpredictable rough idle will disappear when taken out of gear at a stop light. rough idle resumes once its put back into drive. Plug were changed a few yrs.ago. Any ideas/ actions I should take? Thanks!

Your car is telling you there is a problem with the electronic stability control system

I would get the codes read and concentrate on that first

report back to us afterwards, please

Good idea above, that’s where to start. The ESC system may require the engine be running correctly before it will turn on, so the ESC warning may be a result of whatever is causing your rough idle. I expect you read the posts above, that problem was caused by a broken wire to an injector apparently. Finding what’s cuasing a rough idle involves some sleuthing. If one or more cylinders is “miss-firing” that can be cause by

  • poor compression
  • faulty spark plug
  • faulty ignitor
  • faulty crank or cam position sensor
  • faulty injector
  • faulty fuel pressure
  • broken or grounded wire in the harness
  • plugged cat
  • dirty engine air filter

etc, etc …

Well, you get the idea, the mechanic just has to check those one by one. Me, I’d start by testing for a healthy spark at all the spark plugs, then try disconnecting the plug wires one by one as the engine is idling, see if disconnecting one of them produces a change much different than disconnecting the others. Don’t try this if you don’t have the proper level of experience. It’s possible to get a nasty shock, and damage to the catalytic convert is possible.