WallyP

"When it hits the 1600rpm mark the injectors stop firing (can feel the body of them and they temporarily quit clicking) and of course refire once the rpm's hit the 1000rpm mark. Almost as if the rpm's would continue to rise indefinitely if not for some threshhold being crossed, maybe in an ignition map, and so the injectors are dropped out."

This is normal LH ECU function. If the idle switch is made (closed), the LH ECU cuts the injectors off at about 1468 RPM (from memory, may be off a little). I think that they come back on a little lower, perhaps somewhere around 1250 RPM.

MFranke

Thanks Wally. This is very helpful as the rpms were hitting 1600 in my case. It sounds like the idle switch function may be suspect too. I took the hood off last night, got started, and will probably pick up again Monday since I'm off that day.
Thanks!
Mark
88 s4. Auto silver/ black

MFranke

I finished my intake refresh and idle problem is solved. One of the old ISV hoses had developed a hole and was mush and the ISV itself had a lot of gunk in it. Idle now is nice and smooth. The intake refresh gave an unexpected surprise. I suspect maybe the flappy had been sticking or maybe the old knock sensors were putting a drag on things, but I don't remember the car ever being this fast. Power delivery is nice and linear - feels like a rocket sled. Makes me smile just driving it now.