Hyundai Elantra intermittent starting problem (new starter)

Hi, I have a 14’ Hyundai Elantra that has had starting problems. Typically, I would just shake the car and it would then start up, but a few months ago, the starter went out completely. I had it replaced with a new starter and the battery is still relatively new (about 1 year old), but after about 2 months, the problems began again. Today, I wanted to troubleshoot the fuses because it wasn’t starting, but when I returned to the car after about 30 minutes, it started directly. I have often thought that the problem was partly moisture related, and the sun moved onto the car in that time that I was away before it started up. Additionally, the engine began surging when I engaged the 4th level AC (it didn’t when on the other 3 levels); this is a new event in the saga of this problem. I can’t figure out what maintenance to perform. Any suggestions?

Replace the battery cables.

I prsume this is a no-crank problem, you don’t hear the rrr rrrr rrr sound with key in “start”. Ask your shop to measure the starter’s “s” terminal voltage during cranking. It should be at least 10.5 volts. If that measures ok, the current no-crank could a be caused by a problematic replacement starter. Was an aftermarket version used, or an oem replacement from Hyundai? Problems w/aftermarket starters pretty common reports here. I’m just a driveway diy’er, and I’ve had two of them fail right out of the box.

Idle rpm increase w/AC engagement is probably normal. Done to prevent stalling due to increased engine load.

Yeah, I considered the terminal voltage, but don’t have the equipment to check, which was why I thought I’d troubleshoot with fuses in the meantime.
It was an aftermarket starter. I could have that checked again, too (I have a warranty luckily).
The engine surge is pretty serious and is causing the dash to shake a little; way more aggressive than normal rpm increase with the AC.

Pretty good chance the problem is the aftermarket starter. But ask your shop to do the voltage test first, no sense spending money unnecessarily. No harm done to test the fuses, but unlikely to help imo.

When I do that voltage test I rig up a set of long fused lead wires, alligator clips to the s terminal and starter case, and run the other end under the car and into the diver’s seat area, where I position a volt meter to watch as I turn the key. For this experiment, found it is better to use a moving-coil type of volt meter, the type with a pointer-needle and scale, rather than a DVM.

The AC/surge problem could be caused by a sticking/faulty idle air control mechanism. Are you hearing any weird noises, like problematic AC compressor bearings, from the engine compartment when this occurs?

I suggest you clean the battery cables and battery posts using a battery post cleaning brush. Corrosion on the connections can cause the kind of trouble you are talking about. Internal corrosion in the cable wire can also be a cause of this trouble. If those things are okay, then you need to check the safety switches for the starting system. Try starting the engine with the shifter in Neutral to see if that works.