1990 z32 NA auto 2+2 problems

[Zi32]

Alright guys its been a while since i first posted on this forum and since then i have learned quite a bit. but i have seem to have stumbled upon multiple problems all at the same time. first things first i bought this car as the 4th owner and this car has been through a lot....165k on the original motor and transmission, so first things first i changed the basics...oil filter, oil, radiator, radiator hoses, radiator fluid, fluids basically, spark plugs, and even o2 sensors. i will list the problems one by one:
1.) white smoke from under the engine and behind the oil dipstick (most likely from a blown head gasket)
2.) coolant temperature takes a long time to get to operating temperature but when it does it spikes up suggesting an overheat
3.) exhaust smells like straight up gas even though i changed the o2 sensors( i suspect its the cats or it could be something else)
4.)rough idle problem, when starting it up it looks fine and it holds to 1000 rpm easy but give it a few revs and it goes all the way down to 200 and sputters sounding like its going to die.
5.)automatic transmission revs long for first then slips fast
6.)takes about 10 seconds for the car to reach 20 mph( suspecting lost power due to head gasket being blown and cats)


what i want to know is if the head gasket is blown, should i just do a full rebuild or swap to another engine with lower mileage? i was thinking of also doing a 5 speed transmission swap so the transmission issue will hopefully be resolved.
basically all im asking you guys is for tips, tricks, and any golden nuggets of information to get the best out of this z for as cheap and knowledgeable for me as possible. im not a mechanic and this is my first project car so i really want to learn about working on this car. following that if there are any people out there who live around the San Fernando Valley in SoCal who would like to take some time to help out this 22 year old newb work on his project car and teach me, i would appreciate that! thanks for looking at my post and have a great rest of the night

[nissanfreak12]

Well first thing is have you checked the fluid in the radiator(make sure its cold first)? What does it look like? Is it full?

Have you checked the oil? Is it milky or does it look like oil? Dirty oil will be blackish, clean oil will be bronze. Coolant in the oil will look like a milkshake as will the radiator?

Pull the spark plugs, all of them. are they all the same color(probably black soot on them) or do any ones look different?

From what you are describing, it sounds more like you have a coolant line under the plenum that is busted, which is causing the white smoke and you losing coolant. Air in the system will cause a spike and slow to warm conditions. That will also throw off your Coolant Temp sensors. They probably are not reading correctly or have no coolant reaching them until it is too hot. This will also cause your car to run rich, because it thinks its still warming up. It will also make your transmission take forever to get up to speed, because it is running rich.

Your auto has a temp sensor in it as well and if its thinks your are at normal temp but th eengine thinks it is still warning up, it will dump fuel causing it to have a very slow run. Its like you are flooding the cylinders, this will also destroy your cats and O2 sensors.

Check the Ecu for codes, dont rely on the engine light coming on, physically pull the codes from the ECU. There is a walk through on the home page that shows you how to do that. Coolant temp sensor, throttle position sensor both help control the automatic when to shift and how to shift. Swapping a 5 speed may not solve the issues you are describing, but that doesn't mean your auto doesn't have issues.

[Zi32]

I have done what you have told me to do and here are the results:
- fluid in the radiator is topped off with the heater on full blast to circulate coolant through the heater core, fluid is brand new and as it circulates with the cap off, i notice little black specs forming around the hole in the radiator...otherwise the coolant is pretty clean, clear and full.
-the oil is brand new as well and as i circulated it through the engine for a good hour of driving or so, i checked the dipstick and it was bronze and it wasnt milky suggesting there is no coolant leak inside.
-all the spark plugs have been pulled as well and those are brand new too( NGK platinum pfr6b-11) fairly clean and no soot on them at all.
based on what you said about there being a coolant line busted under the plenum there is a high chance that is a possibility, i would also blame the coolant temp sensors and possible wires being eroded and what not. i havent done the codes and will have to consult a professional for that. thanks for the reply and i hope you continue to proovide me with more knowledge! thanks again

[Zi32]

On second thought, i checked all spark plugs again and cylinders 2, 4 and 6 have a thin fluffy black soot around the insulator tip and electrode.....not that dirty but its there... and 1, 3 and 5 are fairly clean with white insulator tips. i read that this is caused due to a high fuel/air ratio and not enough fuel is being burned but its only happening in the left side of the plenum so i dont know what is going on. further help needed

[Rios]

check you vacuum hoses and your maf and tps make sure you dont have any vacuum leaks test your tps and maf...and also for s*** and giggles test your iacv...thats for your hesitation and wacked out idle problems