I just picked up an 86 N/A. I've been trying to get it running a little better, and doing basic maintenence on it. I have done the following:

Oil change
Tranny fluid flush
New waterpump
New plugs

Wires were recently changed
Fuel filter was changed with the motor swap, but I am putting in a new one tomorrow.

It has a Mazdatrix Street port with about 20K miles on it, K&N intake and Racing Beat catback. It has an exhaust leak in the header area that I need to fix.

When I got the car, the idle was hunting. After 50 miles of driving and a slight (less than 1/4 turn) adjustment to the idle mixture screw, it idles steady at 750. I've been driving the car and it has been running better, especially after the plug change. I was going to buy a new 02 sensor and fix the exhaust leak, but today I noticed that the 02 sensor is not even plugged in. The sensor is in the pipe, and the connector is on the sensor wire. After the plug there is a clean cut, and I cannot find the wire to reconnect the 02 sensor.

The car has an off idle stumble, and the 3800 RPM flat spot. I have read how to fix the 3800 RPM problem, but I am wondering about the stumble off idle. It feels like the car "cleans out" and then revs fine past 1200 RPM. Do I need the o2 sensor? I'm sure it is just used for closed loop fueling.. but I'm stumped as to why does not throw a code or run poorly.

The car seems to run well and pull to redline. I'm not really sure how fast it should be, but it seems to have decent power, and will pull to over 100 MPH without issue.

Some addtional info:
The car nearly passed smog as is. It was slightly high on HCs on the 15 MPH test. (I think it was do to the car sitting for 30 minutes before the test). Everything else was fine. I poured some alcohol in the tank and retested and the car passed.

Thanks for any help or tips. Here are some pics of the car.

 

nice fc

 

what gauges are your running in your na?

the 02 sensor to my knowledge is and well your correct is for closed look fueling under about 35% throttle and up to around 3500rpm...
it's just for better apparent gas mileage.
im about to set up my wideband to simulate the narrow band o2 signal and also turn my safc.

but it is important to have and im honestly not sure why it hasnt thrown a code because i do believe there is a code for lack of a o2 signal.

 

It will throw a code. Unfortunately, you won't get a light telling you on your dashboard or idiot light cluster. You have to make an error code checker (simple two l.e.d. lights, common wire, plugs in near your leading coil) or go to mazda (!).

The wire which leads to the O2 sensor comes from harness under the dynamic chamber/upper intake area, so it's hidden under there.

The feedback control system is used for cruising so you may have another more important issure, although I don't remember what the fail-safe reaction of the computer is when it detects a bad/missing O2 sensor. I have to brush up on some of my stuff. BTW, my sig. has links to the FSM so you can help yourself better.

 

I am running Oil pressure and oil temp. I guess the OEM pressure gauge failed and the previous owner put in the Autometer gauges.

 

I need more posts to view links.

 

more

 

2 more

 

done

 

The link in your sig does not work unfortunately.

I could just grab the wire as it comes out of the firewall and connect the sensor directly to that correct? Seriously, I can;t find the wire. It should just be dangling there. There is only 6 inches of wire and a plug on the o2.

Could this be the the reason for my 3600 flat spot - the transition between open and closed loop fueling?

 

Do a search for "3800 hesitation" It's a grounding issue.
EDIT: NVM, I saw you already mentioned that.

 

I'm probably just going to add the extra ground since I will have the soldering iron out anyway.