A friend gave me a 89 240sx hatch SOHC man trans

[balsabones]

Hello all,
I was given a 89 s13 hatch, SOHC with 137269 miles on her. The interior is in great shape and the only rip/tear or crack is on the dash and small tear on the steering wheel. The previous owner, (original), had the engine run hot and replaced the water pump, head, head gasket, stock injectors, rocker rails and rocker arms and all vacuum lines. After putting $2600.00 into repairs he drove the car 1 time and after about 30 miles it quit on him. He asked me if I wanted it and I picked it up from the side of the road. His main problem wasn't the water pump. I found the new rocker arms seized on the exhaust side and from searching this forum, found the culprit to be the oil pump. I installed a melling oil pump and replaced the fuel pump with a walbro, (it still had the original and I figured why not). I also replaced both rocker rails and all the rocker arms. The old rocker arms were so seized to the rail that I had to cut them off. I installed a new battery and got her this past weekend and hit the ignition a few times to prime the fuel pressure. I then went all the way and she fired right up and idled around 1400rpms for about 15 seconds and settled in around 900. I pressed the accelerator and she revved without hesitation. I took my foot off the gas and just let her idle and after about 2 minutes the idle dropped to around 400 and she stayed there sounding ragged for about 15 seconds and then back to sounding normal. she sounded normal for another minute and dropped back to a very ragged idle again. it did this about 4 times before I cut her off and decided to finally introduce myself and ask some question. I have gotten this far with her by using the search and reading just about every tech post. I have tried searching, idles good then ragged" but haven't found anything. Is what she is doing called "limp mode"? Is she dropping into that then back to idling fine then limp....
Yall don't know how much you have helped me so far and I thank all of yall.

[WDRacing]

Welcome to Nico!

In limp mode the engine won't rev past 2500 rpm or so. When the idle drops down can you blip the throttle and bring it right back up or does the motor continue to run rough?

[balsabones]

It continues to run rough when I tap the throttle but revs and revs.
I can let off the throttle and in about 10 seconds or so it returns to good smooth idle for another 10 or so seconds then back to rough. The throttle doesn't change the mode, it seems like the fine to rough and back is in a perfect time though. Like 10 seconds on, 10 seconds off.
I can rev to redline in both modes but slower when idling rough.
after about 10 minutes of back and forth it settles into the rough idle until I turn it off.
When I crank it back up, it does the same thing. I have to say that I let it cool off before re cranking. I will have to re-crank this weekend immediately after turning off.
After it has cooled, (over night), it cranks like a gem the next day and then starts doing the same thing, fine, rough, fine, rough...until it finally settles into the rough and I turn it off.
Edited to add
Thank you for answering my question.

[balsabones]

The best way to describe what it is doing,
it is like the AC compressor has kicked on but with twice the force and then returns to regular idle when it kick off.
I actually though that was it and made sure the AC was off. then after dropping and coming up about 4 times it stayed down until I cranked the next morning.

[WDRacing]

Hmm, sounds like it could be a bad ground somewhere. Have you disconnected and reconnected all the plugs you can reach?

[balsabones]

I have not. I will try that though this weekend. if that doesn't fix it I will get a video of what its doing so everyone can hear it and see the rmps. the muffler is off of it right now and it sounds good.
Thank you so much for the suggestion, I will let you know Monday.
I'm off tomorrow and we don't have internet on the farm.

[jbracy7]

The force is strong with this one

[balsabones]

Thanks jbracy7, I hope the force is good.
I checked all the plugs that I could see from up top and everything is connected good. I unplugged and plugged them back up. If you look in the last picture above, I noticed that the connector going to the distributor wasn't attached. You can see it below the center of the valve cover. I Grounded it. I shot the video and it is uploading now. I shot it upside down, (I wasn't sure which which to shoot a video on my phone).
Here is the video, it starts doing it at 2:18 you can hear exactly what its doing. I don't know if the muffler being off has anything to do with it.
https://www.youtube.com/watch?v=6FCn-vLsclY

[WDRacing]

Watch the temp gauge. It starts as it reaches operating temp and the ecu transitions from open loop to closed loop mapping. In closed loop operation the ecu starts using the O2 sensor. Your car is acting like the O2 sensor is unplugged/broken/bad.

Check that next.

[balsabones]

Thank you so much. I will check it today.
I am also going to go by the auto parts store and borrow the diagnostic tool. I really don't want to remove the kick panel to diagnose.
btw, here in SC we don't have emissions tests and I was going to remove all the emission control components but, like the old saying goes, "if it isn't broke, don't fix it". I know that later on vacuum leaks can occur and hoses dry rot but if it were yours, would you pull all of it out?

[balsabones]

I replaced the oxygen sensor and will crank it tonight.
I hope that solves my problem.
I'm driving a 1978 ford f250 4x4 camper special 65 miles a day. I get 8 miles to the gallon and really need to get the 240 on the road.
Thank yall for taking the time to help me.

[balsabones]

Thank yall for the help so far. I couldn't have got her running without the help of this forum and the search function. I replaced the o2 sensor and the engine temperature sensor. I tried 2 new engine temp sensors and they both made the car crank up without hesitation and idle fine so it fixed the hard to crank problem but she still starts running bad, like in the video at operating temp. I did a self diagnostic on the ECU and it gave a code 13, (Engine temperature sensor circuit) after I replaced the sensor. I disconnected the negative battery terminal overnight to reset the ECU and it gave me the same code the next morning. I checked the new sensor per the FSM and it was good. the old was bad. I started tracing the wires on FSM page to see if I had a ground loose or not connected for the engine temp circuit and found a connector that was not plugged into anything. It is connector E210 on page EL-112 in the FSM. It is supposed to be for the exhaust gas temperature sensor. On the page after EL-118 is the wiring diagram that shows B - R/L to connector-210. the problem is that I cant find the sensor it connects to. On page EF & EC-5, it shows that it is for California models only and shows the sensor near the EGR control valve. The connector is near the starter and the wires to it from the harness are about 10" long. Is this connector on all 89 240s and only connected if California models? if is supposed to be connected, can someone tell me where I can find the sensor? I don't know if this is making me throw the code 13 but I need to find out. I am including pics.
Thank you all in advance.
Edited to say that I also posted on another forum but I have received the most help from here and yalls search function rocks!!!

[balsabones]

found on this forum about the Exhaust gas temp sensor,
ka24e-code-35-exhaust-gas-temp-senor-fe ... it=Exhaust gas temperature sensor#p6391519
It has the same ground as the temperature sensor. could this be what is making the ECU keep throwing code 13?
Does the ECU need to be grounded with one of the bolts that held it to the side of the kick panel?

[WDRacing]

I would always ground the ecu case. Wish I could be more help on the rest. I'm not sure the exhaust temp sensor would cause the poor running.

[balsabones]

Thanks WDRacing, I grounded the ECU and pulled the harness. I then checked the continuity between terminal between sensor terminal B and used a "U" connector to plug into 21 & 29 of the ECU. I had continuity there and also between A and 18 but, the resistance between A and 18 was half what it was on B so I snipped the temperature connector off and soldered a new one on. Its the same connector you replace the injector connectors with for $12.99. I plugged everything back up and reset the ECU with mode V and the negative terminal of battery to make sure, ran self diagnostic in mode III and got code 55, no problem detected. It doesn't stall at the middle point of the temp gauge anymore and all that's wrong now is a little shaking of the engine. Retimed and didn't have to mess with the idle. it was at or a little below 800 with TPS unplugged and 15 degrees, dropped to a perfect 750 and stays there when TPS is pugged back in and stays at 15 degrees. I know I need to clean the throttle body with cleaner, just got to get wife to hold the rpms for me. any ideas as to why I have a little shaking. New plugs, wires, cap, rotor. checked gap on plugs. I can let it idle all day and the temp wont go above the middle mark.