This is a regina injection system. Car has 240k miles and has been recently tuned up.

The idle has been surging for about 1 year now. It will go between 500 and 1000 rpm about 2 times per second. It's very rythmic. This morning it was about 35°F in the AM and the car idled fine at about 600 RPM. When I got to work 30 minutes later though, it was surging as usual. What I've done in the last 6 months:

I've Installed air filter, plugs, wires, cap and rotor.
I've removed the throttle body, cleaned, new gasket, checked Throttle pos switch
I've removed and inspected snorkle tube from TB to air box
I've checked for intake leaks in the flame trap circuit
Intake manifold gasket was replaced ~1 year ago when the head gasket was replaced - also probed entire engine for leaks with propane

I did pull the codes when I got to work and am getting code 2-2-3: IAC signal failure. In my experience, these things are quite robust, and usually its something else thats causing the 223 code. But I think I've checked about everything else. It seems that open loop control works, but closed loop control is causing the issues. Any thoughts?

Thanks in advance,

Matt




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'90 245 252k, '93 945 230k

Wow, is this synchronicity or what? My wife's '93 940 (Regina) has been idling poorly for about a year now, getting progressively worse and finally tripping the CEL. The code? 2-2-3, IAC signal missing or screwed up.

It's doing the same thing as you describe - idle bounces rapidly between 600 and 800 RPM, causing car and driver to bob like a crazy clown car.

Before I got the code, I had cleaned the IAC thoroughly and reinstalled with no change. I then swapped in a known-good unit with no change. I believe our issues are not with the IAC itself, but either in the wiring or ECU control logic.

My plan is to do a little voltmeter probing of the loom to see if I can spot any breaks or signal issues. I have a spare ECU I can swap in if it comes to that.

...according to the green book, which shows a CEL only for:

Regina:
1-1-3 Injectors

2-2-1 O2 signal absent or faulty

1-2-1 Pressure sensor signal

1-2-2 Air temp signal

1-2-3 Engine temp signal

Rex:
1-4-2 Fault in Control Unit

1-4-3 Knock sensor signal

1-4-4 Load signal from Regina CU
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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hmmm...

So I checked socket 6 and got 1-1-1. No problems. Checked socket 2 again, still just 2-2-3. I cleared the codes, ran the car for ~5min and got the CEL again, and the same 1-1-1, 2-2-3 codes show up.

Just for giggles, I ran the DM3 routine and got the expected responses from all the equipment, including the IAC valve. Electrical connections seem good at a cursory look, but I'll have to get in there and verify voltages. I've got the spare ECU if this one looks to be schizophrenic...

I dont get the CEL. But I do get the code 223. I think one of my spark plug wires is 'leaky' so I'm going to fix that and replace the plugs and see what happens. I got a slight shock the other day as I was noodling around with the engine running!!!

Did I mention it seems to run well when the engine is cold... like below 35°F.

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'90 245 252k, '93 945 230k

Well, I got impatient as I have an emissions test looming; I installed the spare ECU I have. The idle smoothed out and stabilized. Was I home free? No. I got the CEL back on, but with a different code this time: 2-2-1, O2 sensor not functioning. I took a look at the sensor and it is pretty banged up from my exhaust misadventures. I'll have to check the output signal and see what's up there next.

I replaced my 02 sensor with a universal fit sensor that was like $30. Just had to do a bit of soldering.... but better than $125 for the direct fit.

There is some good advice in the FAQ abut checking the 02 voltage.

So the ECU seemed to do it huh? Or was it just the re-seating of the connector?????



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'90 245 252k, '93 945 230k

No, reseating didn't do the trick. And now, with a few more days of running under its belt, the new ECU is starting to exhibit the idle instability a bit - though not nearly as pronounced.

You got a generic O2 sensor to work in place of the expensive and unique titania sensor required by Regina? That would be a first. I had a friend try that trick on his '92 Regina, and he had no end of driveability problems that he could not exorcise. I think I'll stick with the OEM for this application. The Bosch sensors are much more forgiving when it comes to using generic replacements.

oh my bad, that was on my 240 that I used the universal fit 02 sensor. It was still the exact same BOSCH sensor as the direct fit just with pigtail ends.

my idle sucks

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'90 245 258k, '93 945 241k

Yes, I noticed that after my original post. I only checked the codes on socket 2.


This would imply that I will find one of the three Rex codes on socket 6 this evening. I'll bet a donut it's not 1-4-3!

According to the Regina Green book, code 2-2-3 doesn't always mean IAC signal failure, it says "absent or faulty". And there's nothing else related to that code, which results when the ECU measures too little or to much current on the IAC ground wire at ECU pin 33.

Unfortunately it doesn't list "surging" as a symptom, only starting problems or low idle speed. And the grounding is internal at the ECU so there's nothing to clean or tighten. But the ground wire (red-black) does run thru an 8-pin connector (C-54) on it's way to the ECU, meaning there might be some resistance there. The book shows the connector to be back in the right rear corner, with the ground wire at pin 1.

The other wires in C-54 are:
2 - green-red
3 - blue-yel
4 - green-white
5 - empty
6 - black
7 - red-white
8 - orange

Also try reseating the IAC connector itself. It might be marginally corroded enough to react to cyclic engine vibrations at idle.



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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks for the info Bruce, I cleaned all connections at the device and in the connector you mentioned, no improvement. I performed the diagnostic test that forces on various devices and I heard the IAC cycle on/off a few times... so its getting juice. I think I'll take one more concerted effort at leaks / gaskets, maybe replace the ECT sensor while I'm at it. Once again, this morniing it was quite cold and the idle was super smooth... thats got to be a clue.

IN other news.... my 240 is torn down waiting for TB, WP, seals, belts. I tore the garage apart last night for an hour looking for my "special tool" couldnt find it. At your advice I;m going to go with the rope trick. Finding TDC sounds pretty straight forward. I removed the radiator shroud and was able to get my impact in there to remove it, but I;ll need to torque to 44+ 60° at reassembly.

THanks,
Matt


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'90 245 252k, '93 945 230k

Does it run any differently if you remove the IAC connection? If it runs exactly the same, but the IAC passes the clicking test in Mode 3 (you touched it to feel it move, right?), then another valve might work better. A valve can pass the full-open full-shut test, which is what M3 does, but not be able to make minor, precise movements.

Good Luck
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1990 740 Turbo, on its way to stock specs, maybe beyond

It just barely, i mean barely runs if I unplug the IAC connection. Thinking about ebay for a used IAC... new ones for the regina are north of $300.



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'90 245 252k, '93 945 230k

My 1990 740 GLE (LH Jetronic) appears to have same issue. At start the engine speed surges up and down and is about undriveable. CEL on and code 2-2-3. I disconnected and plugged off the two vacuum connections at mainifold and problem stopped however idle speed was way down. Then removed and cleaned IAC as best I could as it is sealed unit. Ran and idled fine for 2 days and on the way home 3rd day it started to jack rabbit again. Same code so I plugged vacuum conn's again but still surged. Then I removed AMM connector while running and when I reconnected it idled fine. I would like to know how the IAC can cause engine to surge when it is blocked off but plugged in to ECU? Before I order new IAC perhaps someone can shed light on this. This happens cold or warm but it never gets real cold here (Mexico) never below 75 degrees F