5vz, Rebuild, Replace or upgrade

My 3.4 has 329,000 miles on the clock, and ran like a top, until lately. Occasionally it stutters, at idle and while driving, the stutter is short but hard and usually happens a couple of times then quits. Reliability is key for me as it is my daily driver. So should I try to troubleshoot the problem? Or look at swapping in a used or JDM motor or rebuild? I’ve considered a Toyota diesel swap but that would be time consuming and a little more than I want to do probably.

If I do swap I will probably do the transmission while I’m at it so I don’t have to worry about anything

 

A stutter is not indicative of the heart being bad. Do a leak down test, because chances are your USDM engine is in better shape than some JDM junk that never had the oil changed and rotted on a dock for months if not years.

If the engine is junk, just go to car-part.com and buy a low mile USDM take out from a low mile wrecked truck

 

You should start with the basics like mentioned above. Then you'll find out what needs to do to keep the engine running. Do you have a code reader?

 

I don’t have a reader, I can go to the parts store, but there’s no CEL. I’m a decent home mechanic but I can’t figure out what is causing the studder

 

I'd suggest getting a blue tooth / wifi one if you have a smart phone - they're decent for the low cost:

$22 Foseal Wifi OBD2 Scanner, Car Code Reader Check Engine Light Diagnostic Scan Tool for iOS and Android

https://www.amazon.com/Foseal-Scanner-Adapter-Diagnostic-Android/dp/B00W0SDLRY

Then get a $15-20 app for your phone. Even without one I'd still go with @Itchyfeet's advice to see if the engine is mechanically fit.

 

What about your plugs/wires, MAF, throttle body, etc...?

 

It doesn’t seem like a misfire ( wouldn’t there be a code ) , throttle body and iac have been cleaned within 5,000 miles.

 

Check for vacuum leaks - I thought you would have gone through the regular diagnostics if you had posted on here about swapping out an engine, but it is what it is - you've racked up a fair amount of miles on that mill. Check for pending codes and misfire counters if you can get them from a scanning device.

Since you're at the beginning of the diagnosis then spark, air, fuel, and compression are all possible, but if it's not a regular occurrence, you're right a bad cylinder may not be the case. You can check for spark and fuel if you can recreate the symptoms at idle...