About a year ago my dads 88 3.0 toyota pickup started acting up. it will start and idle rough for just a moment and then it dies unless you pump the gas l, and same goes for taking off in the truck, you must have the rpms up high for it to even roll in 1st gear. White smoke is constantly coming out of the exhaust and I’ve noticed some oil in the throttle body. My dad took the pickup to a local shop and after some time they told us it was getting a knock sensor code so we took the truck back. I tore into it myself and replaced the knock sensor (already speculating that that wasn’t the issue) the old knock sensor and it’s pigtail was bad but after I got the truck back together nothing had changed. I need help figuring out what the problem is. Could it be a cracked head gasket?

 

White smoke is definitely indicative of burning coolant, and considering the 3.0s notoriety for blowing head gaskets, that could very well be the case.
A little oil in the throttle body is somewhat normal on an old engine, as the rings wear and create greater crankcase pressure. If it looks like you just dumped a quart straight into the TB then you may have some more critical internal engine damage.
Have you looked at your oil? Is it milky at all? Does it have a metallic sheen?

 

Color (and smell) of the smoke tells a lot about whats going on. Burning coolant has a distinct smell, kind of sweat, but I grew up around junker cars and scrapping etc. Since the engine has such a lack of power, I'm guessing it's probably missfiring too? A solid test is a compression test on each cylinder, they all should be pretty close to the same reading, generally higher the psi the better. This will tell you if and which head gasket failed, you can change one or both depending how far you want to go with the repair.

FYI, head gaskets commonly fail from overheating, if the cause was overheating, it's possible the head is warped, or in rare cases (and very extreme overheating) it's possible for the block to warp. If/when you pull the heads, check them with a very flat item and feeler gauges. Old school way was a metal ruler.

The 3.0L is known for blowing head gaskets, but out of the 6+ trucks I've had for parts (buying junkers with major problems), only 1 had a bad head gasket, and that wasn't even why it wasn't being driven anymore, it's extremely rusty, like 1/3 of the doors are rusted away lol. One of the parts vehicles has 517k miles on it, low on power, but smooth running yet.

 

the oil looks normal and after I changed the oil it was the clean oil in the throttle body

 

since the motor is old as it is and I’m probably gonna keep running into problems that are hard to identify would it make sense to bite the bullet and get a new engine and have it put it

 

Depends, my dad wants to swap in a 1UZ in his truck (95 T100 with 5VZ), but he works it all the time, the last 20k miles on it were super abusive (12k lb dump trailer filled). It sounds like you have a ton of blow by and the oil is coming from the crankcase vent (runs to intake normally). My dad's truck had a little filter on it when he got it, but soaked in oil. His has quite a lot of blow by too. My 98 T100 with 5VZ has around 220k and it has the typical little bit of oil in the intake, but not super bad. It seems by around 300k they should atleast have the rings replaced. Taking an engine down that far isn't a small job, but isn't impossible. If your willing to do an engine swap, you could throw some new rings in the engine and hone the cylinders. It's not a proper rebuild, but the rings are the life of the engine, and oil is the blood xD.

If you'd like more power and such, the 5VZ should be a pretty easy swap since it's in the same engine family (VZ), so the transmission bolts up to it. You could also go the less common route and get a Camry 3VZ-FE (yours is a 3VZ-E), 4 valves per cyl vs 2 valves per cyl, both 3.0L. I have all of the wiring diagrams for all the newer stuff, I currently don't have the 88 diagram, but have 87 and 89 4runner.

If you go the re-ring route, you'd be installing new headgaskets, so if that's why it's smoking, it would solve that, but it would be best to diag the problems then blindly hoping something will fix them.

Another possible idea, you just did work to it, did you change the oil? If so maybe the oil level is too high causing more oil to come up the crankcase vent and is the source of the smoke and the poor running (too much oil will make it run bad). Burning oil should be more of a bluish toned smoke and should smell like burnt oil (take a stiff of your valve covers, pretty similar smell xD). The fact you can tell the new oil is getting in the intake suggests to me there's too much oil getting there for whatever reason.

If you're worried about how reliable the 3VZ is, I know a guy that him and his friend both bought 4Runners with 400k or so miles on them and drove the snot out of them. He said both came with maintenance logs and around 300k on both had head gaskets done. Both trucks made it past 600k before they got scrapped, I think one was just under 700k. The highest miles truck I have ever bought had a 3VZ in it with 517k. Next highest is from my own daily drivers making it 305k before rust problems (corrola & camry) =). My dad's 5VZ is currently around 320k, he just bought a Lexus RX300 (1MZ engine I think) with over 260k, my mom's Camry is around 280k (5S 2.2L). Toyota makes good engines basically xD. The biggest thing is keep up on maintenance, there's some people that think Toyota = no maintenance at all, like my 1990 LS400 with the 1UZ engine, 20+ years of passing it around the family, only fixing what was critically broken. Original timing belt, wires look orig, distributor caps (yea it has 2) look old, probably original, etc. It has around 230k miles atm. If you want a smooth running engine, go find someone with a 1UZ vehicle. The 1UZ is also known for hitting 400-500k miles no problem, have to love the 6 bolt main design xD.