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Just recently i started a thread where I was getting idle fluctuations and other weird engine running problems. I did get the 12112 code along with 12223.
In the end it turned out to be the AMM. Rodentmaster called that one early on and turned out to be right. If you have access to a known good AMM, you should swap it see what happens.
My idle started fluctuating
 

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Discussion Starter #22
I have very few spares for this car, so I can't just throw one in to test. My idle is steady - in fact, there are no symptoms of anything wrong save for the flashing light. Based on what I've learned in this thread, however, I wonder if that code is in any way relevant to what's causing the CEL. I'm planning to erase it and see if it reappears.
 

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MY 89......not the best year for LH ECU reputation....known more for the fuel pump control failure and other injection faults however, while the indication of 4 flashes suggests an EZK centered issue, I suggest it might be best to keep an open mind on anything related to the LH and EZK until you can obtain some parts and swap out one by one.
Not looking to jump to any firm conclusions but the initial description does not read as the typical pattern of crank sensor failure/breakdown.
The EZK unit is listening for knock.......it's not an overly complicated circuit......some common everyday OP amps (LM2902)....filtered, gated.
EZK constantly seeking to advance the timing to the knock point and back a few degrees.
Somewhere amongst all this, there is a connection between the EZK and LH.......I understand this connection has a voltage or signal indicating engine load.
I am not sure which device originates this signal.
Have you had the EZK box apart? Any hint of water ingress into connector or EZK box?

This is a long shot.....has the distributor been "adjusted"?
While not mission critical, the alignment ensures the rotor and cap electrodes are given the smallest gap/s for the spark energy to transfer.
Cut-out in line with head top surface....as indicated.
274984
 

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Discussion Starter #24 (Edited)
I have not had the EZK box apart, but I did have it out of the car and saw no obvious structural issues that would allow water in. The pins on both the box and the plug were in fine shape. The distributor was out when I did rebuilt the cylinder head this spring, and while I'd like to think I put it back correctly I can certainly confirm it. The car has run fine for months since that work was done, so if it's out of position either it's not far off or the retaining bolt is loose and it has moved over time.

The rudimentary self-diagnostics of this system seem to require a level of understanding and interpretation that I do not possess. Before I started checking codes and such, the way the CEL was behaving made it seem like a TPS issue, since the condition of the light was fully dependent on the position of the throttle: solid on with throttle open, repeating sequence of four flashes with it closed. I realize this is in no way definitive - I simply mention it as an example of how misleading the output of the system can be to the untrained observer.
 

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One thing you can do is unbolt the knock sensor, wrap it in a rag, then drive it.. That can eliminate the possibility of an over-sensitive sensor or other engine noise triggering it.
It;s a long shot but it costs nothing to try.
 

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In line with what Rodentmaster said, the EZK gets a load signal from the LH and sends CEL "data" (gross overstatement of the year!) back. This happens on #2 and #25 terminals at the ECM.

According to the Bentley manual the EZK fault codes only appear over 2000rpm, however I can tell you from experience that isn't true. The sole time I had an EZK box failure on my '86 2-door I got flashes even just turning the key on.

I'd take the comment about '89 ECMs to heart.... The issue simply could be a weird ECM failure too.
 

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Discussion Starter #27
Confirmed the distributor is firmly and correctly mounted. If I have a chance I'll try to get the knock sensor out and bundled up for a test later today.

When I drove the car briefly yesterday, the CEL stayed off. The intermittent nature of this problem makes it difficult to pin down - if I pull the knock sensor out and get no light, is it because I removed a faulty (or at least temperamental) sensor from the loop or because whatever's actually causing it was in a good mood and decided not to act up? Given that it's been in the 90s here lately I'm reluctant to leave the knock sensor out indefinitely - I don't want to start inducing a bunch of pre-ignition because the sensor is wrapped up in a blanket and the EZK advances the timing thinking everything's wonderful when it isn't.
 

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....or because whatever's actually causing it was in a good mood and decided not to act up?.....
My $0.02 ?.....yes.
This might support the theory of wiring or connector breakdown, fatigue, loose joint etc..
Given the scant history of EZK faults, identifying the cause here is likely to require some further digging around.......
Another one from left field.....are you able to remove the LH ECU (RH passenger footwell) and inspect the big connector?
Water can pentrate the loom from the RH fender and end up in the body of the connector.
A post recently (re unusual fuel pump control) went on for some weeks until the owner discovered by chance the corrosion in the connector......pins of the ecu were damaged.
 

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Discussion Starter #29
Took a peek at the LH box - looks like the day it left the factory. Zero signs of water in the area, and no corrosion whatsoever on the pins.

Wondering a little bit about the knock sensor and whether it might throw an error if the EZK couldn't dial back the timing enough to stop knocking. Not that this would be a normal situation, but if I got a batch of marginal fuel and was driving in very hot weather it might. Of course that doesn't necessarily square with the CEL popping on with a closed throttle (does the LH 2.4 system shut off fuel when the throttle is closed?). You'd think this would be evident in reduced performance, but I haven't been driving the car very hard lately - maybe I should go thrash it and see what happens.

Another thought: the car has always required somewhat long cranking time, but it feels like it's gotten longer in recent months. I guessed that this was just a matter of the fuel not being held under pressure in the lines due to some internal leak, but fuel pump problems do not seem unusual in these cars - I wonder if insufficient fuel pressure could be somehow affecting this. Flow can't be a problem, as the engine happily runs right up to the redline without issue (also, the filter is brand new).
 

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There's no documentation to indicate the EZK can identify performance issues, only component issues. I doubt timing etc. is aggressive enough where outside temp is going to be a factor. You could always try a tank of 89 octane and see if it helps at all.
 

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Discussion Starter #31
That's the plan. Tank was nearly full of 87, but I squeezed in four gallons of 93. If that helps, great; if not, I'll wait for it to run down below half and top it up with 93 again.
 

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Discussion Starter #32
Quick update. I haven't had a chance to drive the car much since adding the new fuel, but so far the engine seems to be running a bit smoother and the CEL hasn't illuminated once. I'm starting to think this whole odyssey may simply have been down to bad gas, but time will tell.
 
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