Hyundai Repair: Check engine code...again, fuel pressure gauge, mass flow sensor

Question
1997 Tiberon Fx 2.0L engine, I wrote the other day about the P1128 code, Ichecked for vacuum leaks, there are none, and I even replaced the Air Flow Sensor...big bucks!  The check engine light went out for about 6 engine starts.  Then came back on.  I have not had a chance to have the code checked again, but if it is the 1128 code again, what would be my next course of action?  Per the dealer, there are 3 sensors that could be causing this code, they replaced the Throttle positioning Sensor assembly, I replaced the Mass flow sensor assembly, what is left?  Please advised

Answer
Hi, Brian.  I'm sorry the air flow sensor didn't solve your issue.  Pretty much the only other sensor that could be causing the P1128 code is the air flow sensor.  But I don't recall ever seeing that.  In fact, since you've checked what I've recommended and found nothing, anything left happens with very low frequency.

If you can check the fuel pressure, I'd recommend doing that.  The best situation would be to leave the fuel pressure gauge on the vehicle (making sure to secure the gauge and hoses away from any moving parts) for a significant drive.  In many instances, the fuel pump puts out less pressure as it warms up.  If your fuel pressure is low enough, the computer will need to keep the injectors open longer to deliver the appropriate amount of fuel, and hence will set the P1128 code.

The air flow sensor was a high percentage guess for fixing this code, but further guesses have a much lower percentage.  So if you don't have any method of performing further diagnosis, your best bet is probably to take the car somewhere who can do this sort of diagnosis.  You'll have a better chance of finding the problem with the money you've spent, and you'll be able to apply some pressure to the facility if the repair doesn't fix the car.  Conversely, I don't have the capability of controlling test methods and performing actual diagnosis over the internet.  And as much as I'm sure you'd like right now, you can't put any responsibility on me, either.  Mostly, I don't want you to spend more money and still not have the car fixed.  If the shop that originally looked at the car is willing to look at it again for free, that's a good bet.  Reputable shops who bill for repairs that did not fix the car will at least do this much.  If the shop is unwilling to do this, look for another shop that will stand behind their work.  In this case, your money is best spent being sure the car will be fixed than perhaps choosing someone with lower prices and a less than impeccable record of standing behind their work.