Got it all back together after the intake refresh. Nervous hesitation, pause & prayer. Turned the key and after a couple of cycles; Vroom! Maybe I haven't heard it in a couple of months, but it seems to sound much stronger than before.

What are some signs of a leak? It idles at 750 RPMs. Sounds super strong when I bump the throttle. Would it run bad if there were a leak? I changed everything to include the flappy & TPS bearings.

87 S4 almost ready to be driven again after a two month resto.

Thanks Dewayne & gang for answering my questions.

 

Leak? Hi pitched whistle if its a bad one. If you blip the throttle and the idle sags before recovering- leak. If it is rock steady, could be that you need to re-adjust idle setting / perhaps MAF to correct back to a no-leak baseline. Someone might have nudged the adjustments to compensate for minor leaks that had started to mainfest. Def need to run a few cycles cold-hot and extended use/heat soak before going at the mechanical adjustments, IMO. Have you already done the HVAC vacuum pots?

 

HVAC vacuum pots? What's that?

 

OK...do not allow this to burst your current bubble of euphoria, because it may not be an issue for your car.

The various flaps that direct the air flow for the climate control system function with vacuum. Rubber diaphragms are actuated with switch vacuum to move the arms that move the 'flaps' for the center vent, comb vent, etc. They are fairly often found to be slow or failed due to perforations in the rubber diaphragm, creating a (usually) minor vacuum leak. I do believe there is a thread on here articulating what you should hear in terms of flap movement correlated with the control head settings...but I don't have it committed to memory.

Net-net is that most folks end up going after the vacuum pods (that encase the diaphragms) because of a sub-optimal HVAC, not because of running or idle issues.

There's a dwayne's garage thread on that, too.
http://dwaynesgarage.norcal928.org/1...0Procedure.htm

 

Ok the pods. I changed all of the HVAC diaphragms prior to the intake refresh. I'll run the vacuum test to see if they still hold. I also made Dewayne's tester and will give that a shot also.