Fussy car! Cant figure out this idle problem!
 

1991 Honda Civic Std SOHC ZC

Alright guys you may or may not know I have posted multiple threads regarding my issues.. Sorry.. Okay so here we go once again. I got a jumpy idle, base idle when warm starts out at a solid 800+/- 50, so no problems there. When I start the car the idle is usually higher, and once the car starts warming up it just drops to 800rpm. But sometimes.. well most of the time when its completely warm I will get a jumpy idle, starts from around 1100 and goes to about 1600-1700 (annoying, embarrassing). As well, if I rev:) the car above 5,000RPM the jumpy idle goes away and I get a steady 800. What I have done to try and fix it. Brand new TPS unit correctly adjusted/calibrated. Just installed a refurbished IACV/EACV I tried cleaning my old one multiple times but no dice. I also put in a used fast idle control solenoid valve, which I took off a nice looking motor (was not 100% sure if same gen) at the scrap yard matched it to my old one and cleaned it completely so nothing stuck. Today just installed brand new vacuum lines all around. I have a dashpot, and I do have coolant lines running through the throttle body and IACV. I have an ebay CAI.. I haven't changed the Intake air temp sensor.. (Better not be it!!). New ecu (upgraded to a PG7) I adjusted the idle multiple times to make sure, alt belt is at a good tension, new PCV valve, new gaskets on throttle body and manifolds. Other than that the car runs perfectly.

Carbureted or dpfi engine?

Is the ECU LED blinking a code?

"upgraded ecu"? I'm not sure if you should put anything other than the original one on there, unless you are boosting...

Its a MPFI SOHC ZC 1991 Civic. The ecu is blinking code 20 - electrical overload, I have a small amp for my speakers but I don't think that would cause that code. As for the ECU I was running the stock Si ecu in it before and it still had this problem, and I put in the PG7 from the integra for some more juice to the engine

Code 20 indicates an error in the electrical load detector (ELD) circuit. Do you know with certainty whether or not your Civic has this sensor?

Im guessing it does since it has displayed this code even with the old ECU. Could it be from the swap the original engine was a SOHC DPFI 1.5L

Your ECU may be looking for an ELD that isn't there. This might happen if the ECU is not properly matched to your Civic. The ELD of 5th generation Civics is integrated into the under-hood fuse/relay box (see diagram). Does your main fuse box have an ELD?

Attachment 23004

I dont think I have the ELD the sticker on the fuse box says
15A Condenser Fan --- Fusible MAINFUSE --- 60A Battery
15A ECU --- 50A LIGHT
20A RR Defroster --- 50A IG or LG
20A STOP. HORN
10A HAZARD

FINALLY fixed the idle problem!!!!!!!!!!!!!!!!!!!! After months of spending money and trying everything listed on these forums. I figured this out when trying to test my fan because it wasn't coming on so after doing a diagnostic on it I thought it might be the coolant temp sensor not working properly, so maybe I thought it was connected with the idle problem so I got the car warmed up and it started idling up and down and I went under the hood and unplugged the sensor, the car stopped doing it immediately. I bought a new sensor for about 30$ put it in reset the ecu and so far no problems!

congrats!