Hello all, first time poster here. My daily driver is a 1991 745 with the Regina fuel management system, AW70L trans. and 250k. For the past year or so the car has exhibited a lumpy, low idle while in gear warm or cold. Since the symptoms first began, I suspected the IAC valve as other likely culprits had been addressed. Over the course of the past year, I had installed three different used Regina IAC valves on the car, with the last one being "shiny new" pulled from a recently totaled salvage yard car. The "shiny new" valve was only marginally better than the previous valves.

Out of curiosity, I spliced in a used two prong Bosch valve, pulled from a 2.4lh car. An old Bosch fuel injector connector and pigtail replaced the wider Regina connector for the valve. (Both Regina and Bosch valves pin out essentially the same at the fuel ecu).

Problem solved. The car idles smoothly while in gear, (@ 750ish according to tach in instrument cluster). I have little doubt that a new Regina valve would have fixed the problem as well, for considerably more $! For what it's worth, the Bosch valve measured 34 degrees of dwell compared to the "shiny new" Regina's 29 degrees on my old (and questionable) dwell meter.

I'll try to make future posts less lengthy! Hope this can help someone.

"I'll try to make future posts less lengthy! Hope this can help someone. "

The length of the post was ideal. You explained how you began, how you proceeded, and how you arrived with exactly the detail most of us would need to use this valuable information.

This is an experiment I've had in mind since reading many posts in the 7/9 forum on the same inability to adjust idle theme. But all I have are 240's, so my small collection of used Regina idle valves has not been put to the test yet, in a sort-of reverse of what you did.

Steve should put your finding in the 7/9 help list as a reasonable thing to try as a workaround to those pricey Regina parts.



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Art Benstein near Baltimore

Thanks for the reply, Art. I should add to my initial post that it would behoove anyone interested giving this a try (via salvage yard) to grab the larger diameter rubber Bosch IAC holder as well as the Bosch IAC outlet to intake manifold hose. Though the Regina intake hose was too small for the Bosch IAC, I was able to sleeve the connection with a short length of 7/8 id heater hose.

I can only assume that the used Bosch IAC has a slightly larger open position than the used VDO Regina. (Worn spring acting in my favor?) As for the dwell numbers mentioned above, I am somewhat confused. Wouldn't the duty cycle be dictated by the ECU rather than the valve itself? Though my old dwell meter is certainly questionable, it was (more or less) consistent with these measurements.

I'd be very interested to hear the results of the reversal of this "test", should you ever be in the position to attempt such!

"Wouldn't the duty cycle be dictated by the ECU rather than the valve itself?"

Yes. Or rather the requirement for air as fed back from the EZK rpm number. LH2.4 and Regina would not necessarily use the same duty cycle vs. flow rate, but the feedback needs be able to close the loop over the entire temperature range, reasonable intake leaks, and engine valve wear. I wonder, given that the Regina, using intake air temp and manifold pressure, does not need to meter the air used by the idle bypass, whether that extends or reduces that range over the Bosch system.

I was hoping to be able to measure the goodness of a valve by reading that dwell while keeping airflow constant. About as far as I got was getting a decent breakout cable made for the 3-pin Bosch and comparing my old dwell meter to a modern multimeter with duty cycle function and a scope. I think it began to look like rain, because I didn't learn that much that day, or maybe had a second beer. Had no car problem, and curiosity without necessity isn't as strong a motivator.







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Art Benstein near Baltimore

What engineers say and what they mean by it:
"The design will be finalized in the next reporting period"
We haven't started this job yet, but we've got to say something.

Mighty fine looking laboratory you have there Art! Though I can't quite seem to make out that brand of Yankee beer, I see it's in a red and white can and that's good enough for me (says he who would have been well served by buying stock in the Old Milwaukee brewery...)

"I wonder, given that the Regina, using intake air temp and manifold pressure, does not need to meter the air used by the idle bypass, whether that extends or reduces that range over the Bosch system."

Not that I'm beginning to obsess over IAC valves or anything... but here are my uneducated thoughts on what might prove to be a proper comparison of range attributes between Bosch and VDO valves:

Some scanners have the capacity to display an IAC pulse count (I don't happen to own one) - the higher the count, the more air is bypassed and hence, higher the idle.(Please humor me, I know I'm preaching to the choir -) It seemes to me that with said scanner and a vacuum gauge one could say, start with a Bosch sensor on a Bosch car, idle, record IAC count and vacuum gauge reading. Then introduce a slight vacuum leak, again recording IAC pulse count and vacuum reading. Continue to introduce progressively worse vacuum leaks / recording data untill you feel "enough is enough" (and beginning to worry about the amount of gas in your oil!).

Have an Old Yankee Milwaukee.

Now, repair all self induced vacuum leaks, put the car in gear and record IAC count and vacuum reading. Put a slight load on the engine while in gear (this is why I recommended the beer previously) and record IAC and vacuum readings.

Install Regina valve into the same Bosch car and do it all over again.

Compare results and have another Old Yankee Milwaukee - you've earned them both, regardless of whether the test results amount to anything noteworthy.