I have a 91 honda civic and i need help with the idle up solinoid that kicks in when the a/c compressor turns on. Any body have the hose routing diagram or can tell me where the vaccum lines go to and come from?

 

There is a wire on the AC system that goes into the ECU.
The ECU bumps up the RPM.

 

So are you saying there is no idle up solinoid? Whats the solinoid on the firewall do?

 

This^

If the A/C system is wired properly, clean the IACV and adjust the idle speed.

 

There are a couple on the firewall depending on what you have under the hood.
Take a pic.

Maybe you are looking at the purge-cut solenoid?
That one circulates some of the fuel vapor for emissions.
Vacuum line runs to the charcoal canister.

 

I removed the IACV (which i would have to assume is the 2 wire solenoid on the drivers side of the intake manifold that has the coolant lines running through it). I tested it with a battery and a couple of jumper wires. it works as desired and is clean of debris. When the a/c is turned on the IACV does not actuate. i used a meter and found i only get 4.9 volts to the solenoid. ground is good. no resistance between ground wire and chassis ground. Shouldn't i have 12 volts? I will try to get pics of the actuator on the firewall. I'm thinking it may have something to do with canister purging.

 

The IACV should get battery voltage.

 

Ok well then i guess i better start ohming out the wire to the ECU. The solenoid is controlled by the ECU correct? Any body have a helpful pin out link for a stock 91 DPFI manual trans ECU connector? Is the IACV what the ECU turns on and off to raise the idle for the A/C or am i chasing the wrong solenoid?

 

The IACV gets voltage from 10A fuse 14, not the ECU. I think it's the Blk/Yel wire. The ECU supplies ground for the voltage.

Unplug the IACV. With the key in ON(II), measure voltage between the two pins of the connector. You should read battery voltage.

Also, is the resistance across the two terminals of the unplugged IACV 8-15 Ohms?

 

yes the resistance across the IACV is 11 ohms. ok so the ecu grounds the solenoid. good to know. makes sense. do you happen to know what connector or pin the ground signal come from on the ECU? i will ohm out the power wire today from the fuse block. i measured the voltage between the 2 pins with the connector unplugged and thats when i got the 4.9 volts. i dont think i ever measured between the 12 volt power supply at the connector and battery ground. i will have to do that. either way i will know if i have a bad ground signal or a bad bad power supply.
Thanks

 

The next step is to test the IACV for short. For each sensor terminal, test for continuity to body ground (=short). If there's a short, replace the IACV.

Correct. Now measure voltage to body ground on the Blk/Yel wire terminal.

A11

 

Thank you sir. will get back with the results soon

 

Well I can honestly say that I made an honest mistake. When i put the engine in the vehicle several years ago I plugged the wiring harness back in incorrectly. I crossed the MAP sensor and the IACV. The plugs are keyed the same. Lol. That's why I only had 4.9 volts on the ower circuit. I would not have figured it out if you would not have mentioned the color of wire.

 

I do have one other question that's puzzling me. The 2 wires that come out of the coil. I use to have a tach hooked up to them. The tach stopped working a while ago. I found I have no signal anymore. I get no pulse from the coil when I back prob with a coil. Bad coil? Why does the car still run?

 

The tach signal comes from the igniter unit not the coil. Is the blue wire connected to the igniter unit? If so, the igniter unit, the blue wire, or the tach is bad.