Unplug IAC valve?

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BlueCruiser84

BlueCruiser84

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On a normal running engine (1fz-fe, obd 1) with a presumably good IAC valve what would happen if you were to unplug it while the engine was running? anyone want to do an experiment?

I know what the IAC does and I have read how to do the on vehicle test in the FSM. It passes the resistance test, but I am not sure if it is clicking as described in the FSM.

Any help would be appreciated.
 
It should hold the position it was last in and not move, it's got a worm gear that actuates the plunger.

Pull the plug and try it, why ask someone else to try when you're working on your rig?
 
Because I suspect that mine doesn't work....

Why else would I ask?

I have plugged and unplugged it many times. Driven with it unplugged. No change.

The FSM says you should hear/feel a noticeable click when the key is turned off. I didn't know if that meant it was returning to some neutral position or what. That's why I was hoping someone with a properly running motor could post up their experience.
 
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The only time you'll really notice the IAC actuating is at a cold start during cooler ambient temps when the start up idle bumps up to 1200+ RPM for the first few minutes of operation.

What are the symptoms you're having.
 
I very steady chug in the idle and up through the RPM range. Runs good at WOT. Here is the link to the thread I started:

https://forum.ih8mud.com/80-series-tech/488045-misfire-shuddering-shaking-lopey-idle.html

Since that thread I have had the injectors cleaned and rebuilt, new fuel filter, new (used) ecm, new intake manifold gasket, new fuel pressure regulator, new fuel pump relay, new fuel pump sock. tested and know that I am getting ~12v at all injectors.

I'm getting good fuel pressure at the return hose. The exhaust smells rich, but the o2 sensors tested good and I have no check engine lights.

I have not done a compression test, but I really do not think that is the case as it will randomly run perfect sometimes then just as quickly switch back to running s***ty...

This brings me to the IAC valve. I was thinking if it was stuck all the way open that maybe it would be letting too much unmetered air in.
 
I chased similar symptoms on my '94 a few years back after a HG job and it ended up being a bad injector and crappy aftermarket plug wires. While I had the head off to replace the HG the injectors were cleaned and checked and passed all the checks. I ordered a set of Mr. T wires and it helped a small amount but still had issues at start up, idle and low RPM. Like you I chased every sensor and component that could effect those modes of engine operation and got no where. I even took it to a shop to let them play with it for a couple days, they had zero luck. I ended up procuring another set of injectors, sent them out to the same shop for service and once installed the engine great. I believe I had at least two injectors that despite passing the bench checks were leaking down and not operating correctly. I have to assume something happened to them during the return shipping process. As much is a PITA it may be to pull the upper intake and injectors it may be worth the work to have them checked again or replace the entire set with a freshly serviced set if possible.

It was mentioned in your other thread regarding the injector connectors not latching properly. As a side note in the process of having the intake on/off 3-5 times I did notice the injector connectors were very brittle from the heat, particularly #6 and used .025" safety wire to secure the connectors to the injector but you could use wax lacing cord or if you can get your hands on stainless steel wire approximately .025" you can secure each connector.
 
The "chug" is so steady that I am almost thinking it has to be fuel or spark related. I have an induction timing light and it shows that each wire is getting spark, so unless it is somehow arcing from the boot to the side of the tube I don't think that is the issue.

Which leads me to something that is cylinder specific and non-spark related. I know all the injector connectors are getting voltage. When I put the new injectors back on I zip tied them all into place (it still chugged immediately upon startup). I guess the next step is to pull spark plug wires with it running again and see if I can notice anything in one of the cylinders, though I did that before and couldn't tell.

When I cleaned the old fuel pump relay the thing started up and purred like a kitten. Drove it around and it ran well. Parked it and came back the next day and it was running like crap again. Bought a new one and it still runs like crap... go figure. I am lost (clearly).
 
This may have nothing to do with it but have you pulled the fuel pump assy out of the tank and inspected or replaced the pump inlet sock? It may not be the solution but would certainly eliminate a fuel starvation issue and the bits are cheap to replace.

Grab your FSM and check the resistance of the coils in the distributor just to rule it out. If you still have your old set of plug wires try slaving in the old #4 or 5 wire into each of the positions particularly #6 since that plug in your other thread looked awfully wet. If no change try rotating your existing plugs one cylinder (1>2, 2>3...6>1) on the off chance one of your new plugs is bad. If that doesn't have an effect I think it's time to pull your injectors again. I know I have four or five that are good but I wouldn't hold my breath my wife could find them in my boxes of parts. If necessary I can send her on the hunt if that's the direction you go.
 
In my case my faulty IAC was getting wife 80 lower rpm @ normal operative temp ( less than 400 rpm ) in the cold start not steady rpm then more like oscillating ( up and down ) rpm from 800 to 1200 .. until engine got right temp ..
 
IBCRUSN said:
This may have nothing to do with it but have you pulled the fuel pump assy out of the tank and inspected or replaced the pump inlet sock? It may not be the solution but would certainly eliminate a fuel starvation issue and the bits are cheap to replace.

Grab your FSM and check the resistance of the coils in the distributor just to rule it out. If you still have your old set of plug wires try slaving in the old #4 or 5 wire into each of the positions particularly #6 since that plug in your other thread looked awfully wet. If no change try rotating your existing plugs one cylinder (1>2, 2>3...6>1) on the off chance one of your new plugs is bad. If that doesn't have an effect I think it's time to pull your injectors again. I know I have four or five that are good but I wouldn't hold my breath my wife could find them in my boxes of parts. If necessary I can send her on the hunt if that's the direction you go.
Click to expand...

I appreciate that offer, and may actually be taking you up on it.

Here is what I have learned:

- Number 6 is the cylinder that is misfiring.
- I am getting good spark at the end of the #6 wire.
- Number 6 and number 5 cylinder have the same compression numbers ~200.
It was a s***ty compression guage that wouldn't hole the number but it was giving consistent readings.
- I have proper voltage at the injector plug and at the injector pin on the computer.
- The spark plug for #6 was wet with gasoline and I hadn't run the LC in a couple days. #5 looked normal.

So, I am thinking that there is a short somewhere causing that injector to stay open, though I am not sure if that is possible if I am getting the proper voltages at the computer? OR the injector is bad...



Tapage said:
In my case my faulty IAC was getting wife 80 lower rpm @ normal operative temp ( less than 400 rpm ) in the cold start not steady rpm then more like oscillating ( up and down ) rpm from 800 to 1200 .. until engine got right temp ..
Click to expand...

Thanks. Yeah I am pretty sure it is no longer the IAC valve that is causing my problems, but I appreciate the input. Never hurts to have someone confirm.

Brian
 
Something is fishy with the #6 cylinder ignition. Something isn't right with the cap, rotor or wire. Closely inspect the terminals of the cap and rotor. See if you can temporarily swap the #5 & #6 ignition leads.
 
Yeah, I'm going to swap plugs tonight and see if the misfire changes.

I put a plug in the #6 wire and I am getting spark, so I know it is making it at least that far.

Is it not possible that the #6 injector could be flooding that cylinder with enough gas to make the plug not fire?
 
The only trouble with checking the spark outside the head is the wire may have some electrical leakage that was misfiring to the head or spark plug tube.

It is possible the #6 injector is bad and leaking but checking the ignition is much easier to check without removing the intake and sending out or replacing the injector.
 
Welp, I just swapped plugs and wires from #6 to #5 and the miss stayed in cylinder 6.

I guess this brings me to the number 6 injector being bad, or the computer. I suppose it could be wiring, but with the key in the "on" position I get 12v at the plug on the computer... which I assume means there is no short in the wiring The injector is definitely delivering fuel.. which is evident by the wet gas-smelling plug.

I suppose maybe there could be something down in the spark plug tube causing the spark to jump? Both wires snapped down tightly over the plug... the heater valve isn't leaking, and the cruiser has been inside for the last month.

So which one is the most likely culprit?
 
Order the gasket kit to pull the intake and injector rail. I'll see if the wife can find one of my good spares and let you know.
 
Yeep, I figured that was the next step.

As far as the ECM is concerned, does one signal generator toggle all the injectors? or is there one signal generator for each injector? I'm trying to figure out if the computer could be malfunctioning in a way that could cause this.
 
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I'm sure a few of the other guys and particularly CDan may be able to add commentary but I've read of few if any failures on the ECM. As far as what the injectors timing and sequence is I have no idea.
 
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