high idle when warm

[6e0ff]

I have searched on these forums and read all about the warm-up regulator and the dreaded high idle when warm issue. My car (87 US spec 930) doesn't idle quite as high as somewhen fully warmed up, usually from 1800-2000 rpm. Tapping the gas to see if it is sticking or even pulling up on it with my foot doesn't fix the issue. The other data point is that I get the popping and cracking on decelleration that a lof of folks describe as well. It may be more notiable on the car because it has a spot exhaust on the car. The exhaust and a 1 bar spring are the only mods.

I wanted to see if there are other things I should check, before I drop a bit over $1000 on a new WUR?

[Ronnie's.930]

The things you describe, high idle and lots of exhaust crackling/popping, are classic indicators of a bad deceleration valve (aka - vacuum limiter) except that you say it only does this when warm . . .

Some reading on the decel valve:

Decel valve delete and idle

Idle is high

vaccum limiter

[6e0ff]

I've read some of the decel valve threads too and I was leaning towards the WUR just because it seems to idle fine until it is warm. It is entirely possible that there is more than one issue going on here. If it adds any data, the car will usually idle better when warm if the AC is on. I'm not sure if the extra load from running the compressor keeps the idle down or if there is something else going on. If nothing else, a decel valve is only a $200 part, so that might be the place to start all other factors being equal.

[Ronnie's.930]

It is $530 from Pelican (probably not your problem, however, as the high idle only takes place when the engine is warm) -

Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

[6e0ff]

Ah. Thanks for the correction, I was looking at the wrong part.

[908/930]

Hey 6eOFF,

I don't think your high idle would be caused by your WUR alone, that only controlls fuel somehow you are getting air in there. possible Vac leak or aux air valve stuck open? Have you tried adjusting the air screw for lower idle? Also check ignition timing.

[Ronnie's.930]

I wonder if your auxiliary air valve/regulator (AAV or AAR) stays open after warm-up and continues to allow air to bypass the throttle body . . .

The following is a good thread on the AAV/AAR:
AAR Revisited

[mooney265]

+1 - - you could pinch the line coming from or going to the AAR when engine warm and running. if idle decreases - - that's your problem!

Originally Posted by ronnie's.930

i wonder if your auxiliary air valve/regulator (aav or aar) stays open after warm-up and continues to allow air to bypass the throttle body . . .

The following is a good thread on the aav/aar:
AAR Revisited

[6e0ff]

Cool, thanks for the tips guys, I'll give those a shot and let you know what I find. I've looked around for vacuum leaks and haven't been able to find any so far, but that doesn't mean it isn't that either.

[mark houghton]

I would tend to agree with Mooney and Ronnie. First place I would look would be the AAR, to see if it's stuck open.
In stone cold car, two things are happening to keep her running: the WUR is feeding a richer mixture and the AAR is open to allow more air to support a higher idle. When still cold, that high idle may be around 1200-1500. But once all is nice and warm and the WUR has settled into it's leaner warm mode, if the AAR is still wide open your idle will be very high, over 2000.
In a properly operating car, this symptom (high idle when warm) will occur every time you shut a hot car down for a few minutes and start her back up. On re-start, she'll idle embarassingly high for maybe a minute until the AAR closes back down (it's heat source is an internal heating element which had cooled down while the engine was off for those few minutes).
Vacuum leaks are of course other possibilities, but at least the AAR is easy to test. Do indeed pinch the hose closed...that's a simple diagnostic. Of course if your car has always idled high and this isn't just a new problem, then by all means try adjusting the idle speed.

[aerochip]

I have a similar problem where the idle is very low when cold (maybe 500 rpm) and then goes to around 1200 when warmed up. The AAR definitely works; I think the PO adjusted the idle down so it wouldn't be obnoxiously high when warm. With the a/c compressor on, the car idles around 1000 rpm. I've taken a cursory look at vacuum leaks and will check timing next, but would be interested to know what you found on your car?

[mark houghton]

Originally Posted by aerochip

I have a similar problem where the idle is very low when cold (maybe 500 rpm) and then goes to around 1200 when warmed up. The AAR definitely works; I think the PO adjusted the idle down so it wouldn't be obnoxiously high when warm.

I would be money on that. When I first got my 930, it would idle too low for my liking when cold, and I figured the AAR wasn't opening quite far enough. I eventually adjusted it slightly to get it to open just a little further when cold and raise the idle where I wanted it. Then when fully warm, you can adjust your idle screw to bring it down to the requisite 950 or so.

[6e0ff]

I haven't gotten time to diagnose what is going on with my car yet. It has been a super busy last couple of weeks, but hopefully this weekend. I'll post an update when I have one.