IAC Idle air control valve

[Zuddie]

After I spent an entire week swapping out the tranny in my 1989 Festiva, it ran great for three days. As I was driving home from dropping off my wife at a friend's house, it just simply quit running. Without any tools, the only diagnostics I could do were 1.) check for trouble codes - there were none. 2.) check for spark - nice sparking... not the problem. 3.) listen for the fuel pump... hmm. not a sound.

So I hitched a ride home, got my flatbed trailer and put my Festiva up on it and took her home. I traced the fuel pump through all the way to the airflow sensor. The fuel pump turns on when I move the vane just a tiny bit. I'm not sure if this is normal, because I seem to recall hearing the fuel pump turn on for a period of time just by turning on the ignition switch. The fuel pump also turns on while engaging the starter motor... this I know is correct according to the fuel pump relay wiring diagram.

The problem could still be the airflow sensor, that thing just above the air filter with the big hose running over to the intake manifold. But the other thing I noticed was a humming/buzzing sound coming from what I think is the IAC valve. I only think that because when I unplug it (two pin connector) the humming stops, and I get a trouble code 34.

So the questions are: Is this the IAC valve, located behind the distributor near the rightmost fuel injector? Is the IAC valve supposed to be making noise? I don't recall hearing it before.

Please help... I'm stumped.

Zuddie

[WmWatt]

Not much infro in the Haynes manual but plenty on the Internet. Google "what is idle air control valve"

[mexaspire]

Even if your IAC is faulty, it would not cause the car just to stop and not run at all. If you were removing and changing the transmission and such, maybe something happened with a ground, or a hose or something in the vicinity. You can check to see if you are getting pressure to your injectors and such by using the little valve stem on top of the injector rail. It is there to hookup a meter to but if you are careful, you can press the valve and gas should squirt out. Just be aware that this is not recommended because of the fire hazard but it will give you an idea to see if you have pressure to your fuel rail. If you are getting fuel pressure and spark, you can then move on to testing other things.

Oh yeah, loose battery terminals or connections or the wires to the terminals will cause intermittent running issues. Make sure your cables are in snug into the terminals at your battery.

[firebush357]

The Idle Air Valve is located where you called out. Did the car die as you were coming down from Highway speeds to like a stop sign?

The fuel pump does not turn on with the key like newer cars, it is made to turn on when the Vane moves as you tested. There is a 2 Pin connector in a group of wires near the Brake Booster that you can jump the pins to turn the fuel pump on if the Key is in the Run position so that you can check to see if Fuel is getting to the rail.

Also, make sure to check you 3 Main fuses and you haven't already done it, swap them with Long Leg PAL fuses.

[Zuddie]

I haven't checked yet but one mechanic suggested the the timing belt may have snapped. This is a very good logical suggestion. I will be looking at this in a little while, but thought I'd post it in case anyone else might benefit.

[Zuddie]

Well I checked the timing belt, and that is not the problem... I guess its off to the mechanic.

[1990new]

Some things to thing about:
Things that need to happen for a fuel injected gasoline engine to run:
1. Clean Fuel injected on the downstroke with the intake valve open and the exhaust valve closed.
2. Oxygen containing air sucked into the combustion chamber along with the fuel on the downstroke.
3. Compression of the fuel air mixture in the combustion chamber with both the intake and exhaust valves closed.
4. A spark in the combustion chamber when the piston is at the top of the cylinder and both the intake and exhaust valves are closed.

The IAC is activated by the temperature of the water flowing through the valve. The wires connected to it are for sensor reading sent to the computer.
As stated in a previous post, a bad IAC valve alone should not prevent the engine from running. I don't recall my IAC ever making noise.. but I guess it's possible.

The timing of the spark you say you are getting is critical. That timing belt is turning the cam shaft which controls the opening and closing of valves and also spins the distributor which control when the spark occurs. (The engine computer gets feedback from this also to know when to activate which fuel injector)
That timing can be incorrect because of the timing belt has jumped a notch, the keyway slot has worn on the crankshaft or there can be an issue with the distributor. There also could be a problem with the engine computer but I have never experience a problem with it that caused the engine not to run.

Once you have insured that you have fuel pressure in the fuel rail and the engine still will not run, you can start to work on the other issue if you want to do some more investigating before you take it to a mechanic.

Another issue not mention before is vacuum leak. Make sure you don't have one.

Also could be as simple as a loose wiring harness connector somewhere (or broken wire). Check those especially the ones to the fuel injectors, the distributor and the throttle body.

Just some things to thing about... sometimes it's the little things.