dukenukemx

So I was looking for a replacement Idle Air Control Valve and I came across a Ebay listening where it sells the part for my 85 Porsche 928 but also lists this part for a number of BMW's as well. It looks like the part and claims to fit my car, but I believe the 87+ Porsche 928's use a similar but not compatible Air Control Valve. A Valve for a BMW off Rockauto is still a lot cheaper than places selling a dedicated part for 85/86 928's. Even RockAuto doesn't list this part for Porsche 928's. He's not the only Ebay seller as I can find it even cheaper, though not Zinc coated. I do like Zinc coating. I feel this isn't common knowledge or the sellers are ripping people off.

hwyengr

Looks like it is the same original part, Bosch #0280140509. Fair warning, I found posts on various BMW forums also complaining about the Bosch part going out of production and not finding a reliable aftermarket piece. Buy the Rock Auto valve at your own risk!

The Forgotten On

Get a Lowe replacement if anything. They seem to be at least half decent.

Also, the 85-86 ones are a wear part and do wear out. The 87+ ones do notIIRC but are not interchangeable with the earlier car's part.

dukenukemx

Yea that's what I've read as well and probably explains why my engine has a bouncing idle. It has 210,000 miles and hardly anything looks changed in the engine. The 87+ do look the same, but what's different about them that makes them incompatible? Has anyone tried?

hwyengr

100% will not work, the electronics are completely different. The 85/86 is controlled by a free-floating plate up against an electromagnet. If you put power on one terminal, it snaps shut. If you put power on the other, it snaps open. The control works by modulating the power to the open and close terminals, so the valve constantly oscillates back and forth to maintain the correct opening size. Which is why they wear down, because they're always vibrating back and forth.

I'm less familiar with the 87+, but I think it's a spring-loaded valve that closes with no power, and the duty cycle on the positive pin is what opens it up.

ROG100

Use the Lowe ISV - we sell it for $85 - yes it fits the BMW as well.
2 Year Warranty

Rich9928p

Both the 1985 – 1986 and 1987 and newer idle speed valves are controlled by a pulse width modulation (transistor) switch to ground. The positive voltage is a constant 12V.

bureau13

87 and up, yes. I don't think that's correct with the 85-86. It's a three-wire connector, as opposed to 2. It's really more of an analog device than a digital device like the '87+.

Edit: I went looking for a thread from way back that did a deep dive into how these things work, but couldn't find it. The S3 ISV has an "open" and a "close" pin, and the LH sends pulses on these lines depending on whether it needs to increase or reduce idle. Maybe that could be considered PCM? I wouldn't call it that I don't think but it's still pulsing pins. It's just not the on/off duty cycle 2-wire connection that I commonly think of as PCM. I don't want to go into the weeds on terminology definitions...