Hyundai Accent codes... 5 of em

Question

P1128- fuel system too lean at part load

P0300-Random/Multiple Cylinder Misfire

P0301-Cyl 1 Misfire

P0303- Cyl 3 Misfire

P0121-TPS A Circuit Range/Performance Problem

Im guessing im going to need one coil (the one for cyls 1 and 3), and a tps sensor? Also, im guessing these issues would probably throw the P1128 code, or maybe another issue?

and maybe something else?

Answer 1

You DO NOT have a fuel pressure problem, I promise. Start with the P1128, the lean code.  This is likely the cause of your other problems as well.  On the Accent this code invariably means a faulty Mass Air Flow Sensor - it is a common fault on this car.   Also, the P0121 TPS code sets when the TPS does not agree with the MAF.  That doesn't mean you have a faulty TPS, it means you have a faulty MAF.  That's two codes telling you to replace the MAF.  

Replace your MAF with a dealer part - not a remanufactured aftermarket item.  I hate those.  Once that is replaced clear the codes and drive it.  If any come back treat as necessary.

Wouldn't be a bad idea to throw new spark plugs in it either.  I suspect replacing the MAF will take care of the cylinder misfires as well but if your like most people you are overdue for the plugs anyway.

And thank yourself that you just got $100 worth of diagnostics for free.

Answer 2

Justin, STOP!

Before you start throwing parts at it, check your fuel pressure. I strongly recommend that you check fuel pressure before doing anything else. It would be best if you could check it with the car running or even driving. Make sure you are running about 45 psi while idling and even driving.

I say this because low fuel pressure can cause random misfires to cylinders. It could also cause a TPS code under the right circumstances. I am surprised their isn't a MAP code in there along with them.

Once you have established that you have good fuel pressure you can proceed with other diagnostic routines. But I am banking on the thought you have a fuel pressure issue. When was your last fuel filter change

Answer 3

If you had low fuel pressure then you should be getting fuel related fault codes.... Either low rail pressure, or pump faults that would be causing the problem, or you'd have a leak somewhere.

I think you're going down the right path with the TPS, and the coil. The TPS giving bad signals will totally mess up the mixtures, and is probably the cause of the lean code.