Here is my original thread:
http://www.brickboard.com/RWD/index.htm?id=953436

The problem was that I was getting 4 different OBD codes. Thanks to a few responses, it was determined that the 3-2-1 code is permanently stored in there due to a TSB.

The other codes (2-2-3, 1-2-2, 1-2-1) were not normal. The easiest to tackle was 2-2-3, bad IAC, and it was apparent that it actually was bad. (12V being fed to IAC harness, but no IAC movement/response). I replaced that one with an order from FCPGroton, along with a few other small goodies I had been meaning to get. FCPGroton is awesome! :)

1-2-2 and 1-2-1 were a bad MAP and air temp. sensor. Not good news. However, there were no symptoms. So I did what any other person would have done. I cleared the codes and prayed they did not come back. 1-2-1 came back (bad MAP) but again, no symptoms. I cleared it again. Came back. It was not reappear instantly either. Very random, no pattern as far as I could tell. So I said screw it and reset the code a final time. It has not reappeared yet. I am HOPING that it was a phantom code triggered by a bad IAC, but we will see about that.

The car idles beautifully once again.

Just wanted to update everyone on what was going on and say thanks for all the help. I'll post an update if it turns out the MAP or something else is in fact broken. :)

Oh, and this might be something you want to put in the FAQ regarding the IACs on Regina cars:

Bosch and Regina IACs are NOT interchangeable. According to the FAQ, Bosch IACs have 3 prongs on the harness, whereas Regina IACs only have 2 prongs with a constant 12V supplied to it. I hooked up a multimeter to the IAC lead and as far as I could tell, the 12V is constant, regardless of whether the engine is actually idling, or being revved. This strikes me as sort of odd, because that would seem to indicate that the IAC valve is ALWAYS open, and if that is the case, why even bother having an IAC motor/valve???
--
Ken
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

How much for the IAC?
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john

$250 from FCPGroton, more straight from the dealer.
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Ken
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

Learn something new every day I guess! The section in the FAQ I was referring to about 3 prongs on the IAC is here in case anyone is interested.

http://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm#Intermittent_Stalling_FaultyIAC_or_Hall

When I took out the old IAC and shook it around, I heard something inside rattling. The flap inside appeared to be intact and functioning so I can only assume that whatever was rattling was part of the motor. The replacement did not rattle.

So one last thing I'm still unsure of. ARE the Bosch IACs interchangeable with the Reginas? The pictures of them are markedly different. The Regina IAC appears to be longer and skinnier. If they're interchangeable, I wish I knew that beforehand, as I just forked over $250 for a Regina one as opposed to $150 for a Bosch. :[

Thanks.
--
Ken
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

BTW, the Regina IAC has a constant +12V supplied but is grounded in a step function through the ECU, hence is able to control the idle.

"BTW, the Regina IAC has a constant +12V supplied but is grounded in a step function through the ECU, hence is able to control the idle."

As I posted below, the Bosch LH 2.4 IAC circuit appears identical to the Regina, right down to IAC pins, wire colors, and ECU pins. Perhaps the FAQ regarding non-interchangability, that Invar mentions, needs to be updated?

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

Thanks! Always nice to hear how the problems are solved.

"Bosch and Regina IACs are NOT interchangeable. According to the FAQ, Bosch IACs have 3 prongs on the harness, whereas Regina IACs only have 2 prongs with a constant 12V supplied to it."
• The '93 greenbook diagrams for LH 2.4 and Regina show both IACs as being the 2-pin type. The circuitry appears identical too:
>+12V to pin 1 (BL/Y wire) when the FI System relay energizes at Key On II
>Ground wire (Red/Black) to ECU pin 33.

Maybe the FAC is referring to LH 2.2, which did use the 3-pin IAC.

"I hooked up a multimeter to the IAC lead and as far as I could tell, the 12V is constant, regardless of whether the engine is actually idling, or being revved. This strikes me as sort of odd, because that would seem to indicate that the IAC valve is ALWAYS open, and if that is the case, why even bother having an IAC motor/valve???"
• I'd guess that the ECU can pulse the ground side, and thus control the IAC opening, assuming it's spring-loaded in one direction. Maybe Art Benstein, or someone else who really knows, can confirm or deny this.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Bruce,

My understanding is in tune with yours. The ECU pulses the motor at a rate and duration to balance the inertia of the armature and spring return, providing a variable air gate. Pulsed signals are not easily analyzed with a DVM. Good application for that piezo buzzer.

However I only say this from experience in reference to LH2.4. The one Regina in my life continues to give my mother-in-law complaint-free "drive ability".

One important difference between Regina and LH2.4 controllers I think: LH2.4 has no non-volatile storage. You pull the power, its adaptive memory is gone. The Bendix controller has the ability to retain memory as we became aware of reading the "Regina Programmer" green manual. Not sure of what exactly is kept there regarding adaptive behavior.
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Art Benstein near Baltimore