Questionok already did everything you suggested. I think that the car is running lean mainly because of incredibly clean white spark plugs. if the plugs weren't firing and or the injectors were rich the plugs would be black dirty etc.(I have checked them after letting the car idle/miss for long periods of time.) btw plugs are new autolite platinums. I am also wondering about my idle air control valve. hyundai calls it an idle air actuator assembly. but it costs $200 dollars for a new one.
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My 01 hyundai accent misses during idle and on take off, I have had the codes read multiple times and they are usually random misfire detected but sometimes give a specific cylinder (almost never the same one) the car runs fine at any rpm over 3000 and as long as I rev good before taking off it acclerates fine, but if I try to take off easy it misses quite badly and has stalled. my spark plugs are very clean, and I don't think I have a coil problem. the car seems to be running to lean at idle. I have replaced the map sensor b/c there was a crack in it, but there is no change. I just replaced my before cat o2 sensor b/c the old one went bad and also my intake manifold gasket b/c it was put in bad factory and was sucking air on cyl 4 causing it to miss. the gasket had been bad for a long time, but it didn't start causing a miss until I moved from 8750 ft alt to 4000. I don't know if these things have anything to do with my current prob.
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The number one cause of misfires on this engine is the plug wires themselves. Usually, they track somewhere out the side of the plastic insulator that goes inside the plug tube.
With the engine off, pull each plug wire off the plug and just rest back on the plug without clipping it back in place. Then start the engine and pull each wire off the plug separately and return. When you pull the wire off the plug, you should see spark jump from the end of the wire to the plug terminal. If it leaves the wire anywhere other than the end of the wire, then you'll need new wires. If it arcs at the coil, you'll need a new coil. If it arcs between the coil tower and wire boot, you're probably best off replacing the coil and wires.
Even though your plugs are clean, if you don't find anything above, you should probably consider purchasing a new set of good name brand spark plugs. Denso and NGK are excellent plugs. It's cheap and will give you an answer fairly quickly. I've seen many plugs arc somewhere inside the plug, resulting in the spark never reaching the electrode.
Unfortunately, I'm not as confident as I'd like that you'll find anything with the above. Secondary ignition misfires typically reset the same code. If you have a history on which codes were set at what time, and what was done to the vehicle between each instance of codes, that may help understand the problem as well.
You might also check for vacuum leaks, especially the PCV hose. This would cause a lean condition, and could cause a misfire as well. Additionally, its effect at higher rpm would be minimal. You should probably also doublecheck the intake manifold gasket to be sure everything is sealed properly. Out of curiosity, what makes you think the car is running lean?
AnswerThe idle actuator should only affect your idle speed. I've seen situations (although not on Hyundai) where the idle speed dropped so low that misfire codes were set. If your engine idles at normal speed, misfiring or not, it's very unlikely your idle actuator is bad. And I don't think I'd try that for $200.
Clean plugs don't necessarily indicate a lean misfire. A rich misfiring cylinder will simply have unburned fuel and hence a wet spark plug. Although I've never used them myself, I've not heard anything bad about Autolite plugs.
This is an instance where a scan tool would be of assistance. The fuel trim values will be instructive. Positive fuel trim numbers mean the computer is adding more fuel, and negative fuel trim numbers mean the computer is taking away fuel. This will tell you what type of misfire you have.
Your description doesn't really sound like anything I've seen before other than a vacuum leak. Are you sure it's actually misfiring? Is it possible it's just running odd? How soon do the misfire codes come back? Is the idle speed normal?
My first instinct on hearing that you were considering spending $200 on an idle actuator was that the money may be better spent on having a professional diagnosis done. And I mean diagnosis by a shop with the utmost regard in driveability and check engine diagnosis. It's possible that it'll be cheaper at this point to pay for the diagnsosis and then do the recommended repairs on your own. Right now, my biggest difficulty is that I cannot feel what the car is actually doing.
