Hey, I'm new to the forum, but I've got a serious problem.

I recently bought a 1990 EF civic wagon that came with a mini me VTEC swap. The engine runs strong, but has idling problems.
On start up it has 1100rpm then drops to 400-500. Then after driving a while will drop to almost nothing, making the whole car struggle to keep running. Other times the check engine light comes on and gets stuck at 2100rpms!! I will turn off the car and the system will reset without the check engine light.

But the worst part is the mileage. I only get about 120 miles a tank
I changed the air filter, oil change, and spark plugs. The spark plugs that were in before were black, and now so are the new ones. So the engine is obviously burning fuel and running too rich also resulting in a black exhaust..

People keep telling me it might be the O2 or barometric sensors, but how do I know for sure? Shops say since the codes wouldn't match up, they can't check the sensors. They all get freaked out cuz it's a "Frankenstein" swap.

My car is wired OBD1 with the right distributor and P28 ECU, so what could it be?

Timing?
Sensors?
Electrical?
Intake and exhaust?
Needs new manifolds?

Someone please give me some input, cuz I don't have the cash or resources to replace a part not knowing if it will fix the problem or not.

OBD1
D15b7 block
D16z6 head
P28 ECU

 

You have a jumper harness? When i had my jumper, there was 2 wires a blk and yellow, you connect them together to read codes.

Make sure you have the 4 wire o2 sensor. A bad o2 can cause your car to do some crazy stuff.

 

you probably need a new fuel pump .get a new O2 sensor , make sure you buy a Bosch with the correct connector , makes a big difference .they are only 28.00 or so why not put one in .