Hello, ive been reading tons of threads about this topic so i know its been covered many of times. However i just want to be certain before i purchase an ecu.
I have a 1990 lx sedan obd0 dohc zc mpfi swapped, i bought it "as is" not running. So every time i drive my car it has a bouncing idle once its been warmed up, a couple times its done this on a cold motor after running for like 10 mins on a very cold morning. Cold start it idles at like 1900rpm and slowly comes down to like 1300-1400rpm and temp guages starts to go up slowly because rad fan is jumped. Then the idle will slowly drop down to 900rpm for a minute, all the sudden rpms kick to 1400pmss ish and bounce back and fourth from 900rpm-1400rpm.

What i have done: Overhauled the motor, bored it out to 75.5mm and got thicker cometic head gasket to keep compression around 9.6:1 which i believe is close to oem, correct me if im wrong.
New timing belt, water pump, new ect sensor.
Currently have the rad fan jumped to be on when ignition on(was this way when i bought it, i suspect it might be causing issues because takes forever to warm up to operating temp, i bought a new switch just need to install it)
Ive gone through and fixed a lot of the old sloppy wire connections from the mpfi swap.
Found the oil pressure switch is unplugged and wire was tapped off like the sensor was bad and old owner just tucked it out of the way idk. Havent fixed that yet.
The whole cars harness is messed up, not corrosion but splices everywhere for aftermarket alarm, stereo, and dpfi to mpfi,
Ive debated rewiring the whole motor back to the ecu but i cant find legit diagrams for pm7 wiring. If anyone has those that be awesome.
Mechanical timing is set. Ignition timing is probably off a little. currently my timing light is broken.
Installed new IACV,
Fuel pressure regulator to 40psi, injectors look little dirty but all spray.
Spark plugs are black and im on my 3rd set in about 1500 miles on rebuilt engine.
Smokes at idle but doesnt burn oil, pretty sure its dumping fuel because gas mileage is way down. Accelerates smooth but feels down on power kinda sluggish.
Ive reset tps to closed .51v and wot 4.49v far as it goes cheapy one.
No check engine lights but i have a code 14 on ecu. Check engine light comes on with fuel pump on start up for 2 seconds.
Ive put hours into fixing this car and just want it to run right.
I have checked voltage at iacv while it is boucning idle and it jumps from 9.5v to 10.8v so it is moving, unplug it and the idle drops to normal base idle but sound super rough like super rich.
No vacuum leaks i have checked everywhere multiple times.
Also i do not have a FITV, only one port inside TB for IACV.

The ecu controls the ground on the IACV circuit am i right? So if the ecu was internally messed up and couldnt get the resistance right or whatever then my IACV wouldnt operate normally right?
Everything points to the ecu, I just really didnt want to replace it because its a legit PM7 and there hard to find for a good deal.
Somebody has to have ran into the same problem before.
I tried to attach video but couldnt. Its on my Instagram rn @blakebuilds or i could send it on fb.

 

it is not a problem with the ECU - if you disconnect the IACV, the idle should drop down to around 500 rpm and remain steady - if it does, the IACV is o.k. - problem is elsewhere - most likely a vacuum leak - could be the PCV valve not working correctly - looking at the picture of the engine in your other thread, I can't tell if the vacuum port (closest to the passenger side) on the front of the intake manifold is capped off or not? - that port is for a vacuum line to the idle control dashpot on the throttle body, which appears to have been removed

 

I have the dash pot removed and vacuum line capped off. It did same thing with it installed. Does a dohc zc need the dash pot to idle correctly? Ive read some people delete it. I thought by capping off as many vacuum lines as I could would rule out a leak. Also i have pinched the pcv while it was surging and same thing no change.

 

it doesn't need the dashpot to idle correctly

 

did you replace the rubber double o-ring gasket when yo replaced the IACV?

 

Yes new o ring. Going to check for vacuum leaks when I can today.

 

also, check to make sure the correct connector is plugged into the IACV - both the IACV and IAT sensor connectors are 2-wire connectors that can be switched - the IACV connector has BLUE/YELLOW and BLACK/YELLOW wires - the IAT connector has RED/YELLOW and GREEN/WHITE wires - IACV connector is GREEN in color and the IAT connector is WHITE in color - a lot of people get these switched when converting from DPFI to MPFI

also, reset the ECU to clear the Code 14

make sure it is completely full of coolant - low coolant level can also affect the idle

 

Okay ive cleared codes and checked for vacuum leaks didn't find any. With no codes engine still idles high at like 1400rpm. Drives without surging for about 10-15 mins or until operating temp is reached, then suddenly while at 1400rpm idle drops to about 700 and bounces back up to 1400 over and over until car shuts off and code is cleared. Ive followed a flow chart from honda and says to try a known good ecu and see if changes. I though of using a rheostat to adjust the iacv but I understand the ecu needs to control it while at idle and when loads kick on. I did check the iacv and iat and they are the correct plugs and wires to my knowledge. Idk how far back in the harness the previous owner exteneded the connections. Also my exhaust smells very rich. Im almost to the point of pulling the engine just to re-wire the whole car. I know you said you don't think its the ecu but have you come across an idle surge where the ecu was infact bad? What were the symptoms?

 

Alright so far its not doing the bouncing idle issue anymore. Cleared codes and ran a new wire from iacv blue/yellow to ecu pin A11. Still have high cold start idle around 1900rpm but when at operating temp idle is at about 800rpm.