AlexGarci

Have a weird misfire issue doesn’t misfire at idle or nothing but once I accelerate it begins misfiring and hesitates to accelerate. got code p0303 replaced spark plug, coil pack, fuel injector and checked for any vacuum leaks? Only thing I can think of is spark plug wires has anyone had this problem?

TrueGS300

I and others on here have found that at this age, the wiring in the harness for the ignition coils has become brittle and loosing the insulation around them causing shorts. You may need to go into the harness and rewire the coils one at a time.

KTGS300

Check this first.

I had this exact same issue and it was the insulation of the ignition coils wires. Also, make sure you label the wires and put them back in the same position. I flipped the pair of wires for one of the ignition coils and it took me a while to figure it out.

reezekeys

I forget the exact code I got, but my symptoms were similar and it led to replacing a "variable valve timing solenoid." It felt like I had a new car after this! The acceleration was much improved.

There is also a screen associated with this part that gets clogged, I've seen youtubes on cleaning it. That only costs a little time.

sbagdon

Is that a statement or a question?

P0303 is "Cylinder 3 Misfire Detected". Sounds like good advice to do all the wiring cleanup suggested above, and replace the electronics you can... the car is 18yo after all. Our GS4 has coil-over-plug, so we replaced our plugs (probably original, from 200k+ miles ago), and you could feel the difference.

OCV issues will usually throw code P1349 or P1656. When we were having OCV/P1349 issues (root cause of mis-timed timing-belt), we had bad idle and stumble at constant throttle, yet no mis-firing. We could get rid of the idle/stumble issues by unplugging the OCVs (which the previous owner had done, and broke a plug in the process, we plugged them back in to fix the problem), yet lost some power. We replaced the plugs and OCVs before fixing the timing-belt timing issue, so we can't attest to how they were with a properly timed belt, yet no misfire before/after the timing fix.