Hyundai Repair: 2000 Accent - hesitation, spark plug wires, hesitation problem

Question
Hello,

I drive a manual 2000 Hyundai Accent with 61000 miles and a 1.5L SOHC engine.  Right now my check engine light is on and my car hesitates when low in gear.  I first noticed the problem a little over a month ago.  I had Autozone read my check engine light and they said cylinder 1 was misfiring.  I replaced the spark plugs with manufacturer plugs and the spark plug wires with aftermarket wires from Advance.  However, the check engine light came on again and again I had it read by Autozone.  This time they read me the code P1128.  A couple days later my car started to hesitate severely, so much so that the check engine light blinked both when the car was idling and being driven.  The hesitation was worst in the morning.  I brought my car to a mechanic that I trust and he said he couldn't find any performance problems.  He kept the car overnight and the next day it didn't hesitate nearly as much as before I had brought it in.  He told me to use a fuel injector cleaner (which I did) and if that didn't work, I might need to replace the fuel injector.  For about a month now the car has run pretty well.  I replaced the fuel filter this past weekend.  But, 2 days ago the hesitation started back up.  I’d really appreciate any suggestions for fixing the hesitation problem.

Thanks very much for your help.


Answer
Did the mechanic recheck the codes again?  If the check engine lamp is flashing, the computer is detecting a misfire.  The codes currently present, the freeze frame data stored at the time the initial code set, and the current ECM data stream are key to figuring out what is happening to this vehicle.  If your mechanic cannot access all these things, he's not the person to address these issues.  If that's the case, since you trust him, perhaps he can recommend someone equally trustworthy who is equipped to perform check engine and driveability diagnosis.

Anytime you have a misfire, the first things to check are the secondary ignition components (plugs, wires, coil).  It's possible one of the spark plugs you put in was defective, or one of the old spark plugs was carbon tracked, leaving a track in the wire as well, which has now transferred a carbon track onto one of the new plugs.

For the P1128, the primary items to check are the PCV hose and the air flow sensor.  If your PCV hose is leaking, it'll cause a hesitation and the P1128, but not a misfire.

Since you have a P1128 along with a misfire, it's a good idea to check your fuel pressure.  If your fuel pressure is low, the computer must hold the injectors open longer, and thinks it's delivering an abnormal amount of fuel, setting the P1128 code.  If your fuel pressure gets too low, the injectors won't open properly, and this may cause a misfire.

Finally, there's a reprogram available that corrects a poor acceleration condition on cold starts available at the dealer.  But since your check engine lamp is coming on, you'll need to address those items first.  Based on the information you've given, the cause of your check engine lamp is the most likely cause of your hesitation.