91 Metro still rough idle

[gungadin]

Hey Rick I'm in the water biz too. Good luck today,
I think winnetcom has the best idea.
I rescued and rebuilt my '93 metro from the blackberries down on the coast in Port Orford. It's the most faithful car I've ever had. Man what a money saver eh? I've got 55K on my re ring hone head and rod bearings.
The oil is very clean and clear.
My machinest told me that the lighter 5W30 is necessary for the valve train. He says the heavier oil doesn't allow the valves to fully close and causes them to burn.
Nice weather eh? We're making 60 milliion gallons a day of drinkin' water for the last two days. I tell you these people are THIRSTY!!!

[winnetcom]

This is the kinda tip I was looking for :^) The strange way my car runs as indicated in the start of this thread may be caused by a bad ground. That could explain alot. Seems the coil is kinda close to the ground from the destributor, sometimes arcs if I pull a plug wire. I have suspected from the start that area could be a problem... I'll check it out thoroughly.

Originally Posted by gungadin

Hey here's something easy to try. There are a couple of ground wires from the engine to the firewall up high near the center. Try re-establishing a good connection with these and also the screws that hold the coil to the firewall. And any other electrical device that is mounted to the firewall.
Also one of the ground wires has a connector about halfway. make sure it's tight.

[physhop]

Okay mine did exacly the same thing. There is an ISC solonoid on mine that increases the idle speed under an electrical load. On mine the solonoid valve and the computer output that controls it were both bad. I replaced the valve and restored it's operation with a relay since that one output on the computer was shorted. Now it works fine, 45mpg and smoothe idle too. I can give more detail if interested. Mine was a canadian model with manual transmission. Not all models have the same idle speed control.

Larry

[DanMan7]

When you say the output on the computer was shorted, how did you fix that? Did you replace the computer? Or are you talking about inside the ISC? Let me know, thx.

[physhop]

HEY DanMan,
Sorry I’ve been gone awhile. I’ll try to explain.

HOW IT WORKS
The idle speed control (ISC) solenoid is an air valve that lets extra air into the throttle body just as if the throttle were slightly open. On my 91 metro it increases the idle about 110 rpm. It only comes on when a load is present and allows the engine to idle smoothly with a load. The valve is powered up from the fuel pump fuse and has power whenever the fuel pump is on. The ISC valve only comes on however when the computer senses a load. When a load is present the computer grounds the solenoid valve so it comes on. The way the computer senses a load is unique. There is a block of several diodes in the wire harness near the inside fuse block. Several circuits are wired to the diodes so that if any one circuit is on, power comes out of the diode block to the computer. When it works right, the computer gets about 12 volts at the sense terminal when the headlights, brakelights, radiator fan, or heater blower get turned on, then the computer grounds the solenoid to increase the idle speed.

WHAT I DID
When I replaced my ISC solenoid, the valve was always on and the engine idled too fast with no load. I found that power was present at the computer sense terminal only when an electrical load was present as expected. However the ground connection from the valve to the computer was always grounded. Either the wire was grounded somewhere or the computer output was shorted to ground. Disconnecting the solenoid ground from the computer made the valve go off so the wire was not shorted to ground.

RESTORED ICS FUNCTION WITHOUT COMPUTER
I realized I could restore the ISC function with a simple relay and all I needed was a 12 volt relay and an additional ground wire. The coil of the relay gets the power from the diode block on one side (this was the sense wire to the computer). The coil is grounded on the other side. The relay comes on when a electrical load is present. The normal open relay contacts are hooked to ground on one side. The other contact is hooked to the ISC valve (this was the wire from the ICS output terminal on the computer). Now when a load is present the relay comes on and the valve comes on.

RESULT
It works great. I can’t believe how much better the car drives. Smooth idle at load and at no load. I get about 45mpg. I hope this makes sense.

Larry