Danapsta

I have a 93' 300zx N/A which recently had a new(ish) engine put in it. Needless to say the people I took it to didn't do a good job at putting it in at all and ive been back several times since and the problems are only temporarily fixed if at all. I'm going to list the problems I am having just for input on what it might actually be and if i can improve on them myself. (I am not mechanically savvy)

First, when I start up the car it revs up like normal but when the rpms drop back down I have to give it a little gas or it will most likely die. Also if it hasn't been driven overnight or for any period longer than 6 hours it has a bubbly feel with the exhaust and gas. What I mean is when I accelerate the exhaust cuts out rapidly and has no power for about 1 sec then will accelerate, and it will do this after every gear change when I get back on the gas. Makes quick take offs impossible and cooler weather makes it worse.

Second, my fourth gear grinds every time I shift into it. It is the only gear that does this and it doesn't matter how high the revs are, how long or hard I hold the clutch down, or if I double clutch. Also sometimes it will make a grind-like noise when accelerating in 1st and rarely 2nd and even sometimes have a constant grind when idling in neutral.

Third, the car will sometimes die at stop signs when the clutch is pressed in. This is much like the first problem because it will die when the rpms drop. This doesn't always happen, but it has been happening more often lately. Also (the rarest problem) when it dies, sometimes it will not start back up without a constant ignition crank of about 20sec. It has left me stranded with this problem multiple times before and the people did make it "better" but it will still do this from time to time.

There are other problems too but I have a good idea of what is causing them so I wont list them. These are the ones I cant figure out and apparently neither can my mechanic. I don't have the money to constantly be bringing it in so hopefully I can get some input to narrow it down.

What I know: Last oil change I had the tranny fluid checked and they said it was very low and refilled it. A few buddies of mine mentioned something about the temp sensors or throttle position sensor causing the power loss. I have no idea what these are. Lastly, I know it has spewed has out the hoses on top of the engine before because they are rigged up badly.

Any more input is appreciated, thanks.

hoov100

o2 sensors. does it throw a check engine light if you cruise at 2k RPM for a bit? Also run the ECU codes.

Danapsta

No the check engine light never comes on I've never seen it cone on. Also Idk how to check ecu codes.... I'm not engine savvy but know the basics

hoov100

Google "300zx ECU diagnostics" It sounds like o2 sensors to me.

Danapsta

Alright thanks I will check that out. What do you think is wrong with the transmission? Going out?

clickdoc

Both times my O2 sensors went bad - NO check engine light - but came up when running codes !