1990 LX sedan, all stock d15b2 DPFI. Idles high when in park,(auto trans). but idles ok on drive. Also, if I turn my headlights on when in park, the car idles normal, as soon as I turn them off, idles go up to about 1200RPM. Any idea on what this could be?

 

Yep.

First check the engine harness ground point.

Top off radiator fluid. let running at idle no heat until the fan comes on and goes off. Then take a 10mm wrench or socket and crack the air bleeder valve located atop the water neck and let any air out. Repeat if necessary. Should let run about 15 seconds.

You may also need to check you ELD. Easy enough to look up and test for.

Last but not least is to adjust your TPS. Better let a technician do that one for you.

You can google for this info.

Good Luck.

Peter

 

Since you have OBD0 you can lift the carpet on pas side floorboard and see the ecu with its red light flashing. Reading this and looking up the codes will be more helpful than anything else. The red light blinks. X X X X= 40 , XXX= 3. Together they are code 43.
What is ECU code 43 90 civic.

 

I have the radiator fan on wired directly to the batter and have a switch in my dashboard for it. I have just also changed the thermostat and changed the coolant and bled it also. I made sure the ground to the thermostat case was on tightly. This started before I did the thermostat change.

 

Try cleaning your IACV. https://honda-tech.com/forums/honda-crx-ef-civic-1988-1991-3/how-clean-iacv-dpfi-idling-problem-2443124/
-Later, BR

 

Forgot to mention that I have also cleaned the IACV, used Seafoam spray to clean it, took out what seemed carbon deposits, used a pipe cleaner to stuff into the IACV lines.

Could a vaccum leak cause this? I think I hear a small whissing sound coming from the back of the throttle body.

 

Most certainly. A vacuum leak could cause this. Spray a bit of WD-40, seafoam, water, ETC around where you believe there might be a leak. If any change in Idle, you found one. -Later, BR