2,800 RPM at Cold Start?

[mooney265]

With 70-Deg. ambient, my 930 idles at 2,800 rpm at start for the first 1.5 minutes. Then, it slowly goes down to about 1,100 after 2.5 minutes.

Is this normal?

Also, if i shut the "warmed up" car down for about 10-minutes, on restart the rpm's go back up to the 2k range for 1.5 minutes. Even though the car has already warmed up...

Is this normal?

Thanks - Shannon

[mooney265]

I just read that Johnny Walker has recommended using an AAR from an SC. Has anyone had any luck with this?

[mark houghton]

First thing, make sure your idle at fullly warm is adjusted down to 950 rpm, using the air correction/idle adjustment screw in the far back reaches behind the intercooler (a real pain to get to). As to the action of your AAR, it sounds to be working as intended; i.e., being fully open and letting in maximum air when the engine is cold, slowly closing as the engine warms up, and beginning to open back up after the engine's been shut down for a few minutes...thus the high idle for a short period even with a previously warmed up engine. These AAR's have a heating element to keep the thermo spring warm enough to fullly close, and this along with the engine heat keep it closed while running. But when you shut her down, the residual engine heat isn't enough to keep the valve fully closed and it will start to creep open again. It's just one of those little idiosynchrasies of the 930.

Unfortunatley the AAR is not intended to be adjustable. If you've got your fuel mixture and idle set correctly, then theoretically the AAR will function as intended. If you can't get your hot idle down to 950 with the idle adjustment screw, then it's possible the AAR isn't closing completely. If that's the case, try installing a PCV plumbing valve in-line with the air hose leading to the AAR and close it down to limit the amount of air it delivers. Or, remove the damn thing completely and plug all air lines. The downside of this approach will be a low cold engine idle.

[jly535]

My 77 930 was doing the same, I just removed the AAV and plugged the two hoses together with a piece of solid aluminum rod. I just use center console throttle cable/choke to start. A little cold blooded to start but idles perfect when warm and no more high revving cold start.

[fredmeister]

Mine does the same thing....wierd that on a warm day like 70 degrees out, it idles high after even shutting down for only a few minutes to get gas or something like that.
I checked AAR valve and it functions fine. Needed to clean the electrical contacts on the snap on plug connector, and checked for hose leaks. All ok, I just accept that it is normal.
What can you do for 1979 technology. I would not bypass it, too difficult when the weather really gets cold.
Just put up with it till the car gets fully warmed up.

[mooney265]

I appreciate all the replies! I think I'll adjust my warm idle down to 950. Then, see how much that lowers my cold idle speed.

The only issue I have with this high idle is getting the car in reverse with the high revs... It doesn't want to go "smoothly" when rpm's way up there... Maybe, just learn to do cold starts in reverse, when reverse is initially needed...

Also, I have a digital AFR gauge hooked to a wideband O2 at my new B&B header. I notice that my warm AFR's are running at about a 13.5 AVG. Maybe this is a little low?? And, because it's a little low, it's a little rich - - - - - - soooooooooooooooo, when the AAR introduces the extra air, it mixes with a rich fuel mixture and make the idle a little higher than necessary???????

Well, I guess that's a stretch....

[jly535]

Try shifting to 1st then 2nd then reverse, this should avoid grinding, Jamie

[mark houghton]

Also, I have a digital AFR gauge hooked to a wideband O2 at my new B&B header. I notice that my warm AFR's are running at about a 13.5 AVG. Maybe this is a little low?? And, because it's a little low, it's a little rich - - - - - - soooooooooooooooo, when the AAR introduces the extra air, it mixes with a rich fuel mixture and make the idle a little higher than necessary???????

13.5 AFR, I presume you mean at idle, really isn't all that rich. In fact, it's the opposite of what you're thinking. The lower the AFR, the richer the mixture. So, perhaps with your idle AFR where it is, the extra air is making it leaner still and raising the idle. I don't remember, but I think 14.-something is the stoichiometric optimum for lean best idle/fuel economy.

Try adjusting your idle, and if you have acess to someone who can test your exhaust emissions, it will help to make sure you're in the ball park on CO%, and ultimately AFR's. Oh, and don't forget to check your ignition timing to make sure it's spot-on. That in itself can result in higher idle rpms.

[Miguel Antonett]

Mine drops the RPM's within, I'd say 20 second when stone cold start - a little longer during the winter = below 40* or so - and I haven't noticed when warm because I crank and go.
At first crank - cold - to get out of the garage I put it in reverse first; this allows to eliminate the grinding you refer to and also less friction on the starter.

[JFairman]

Lower your hot idle speed to around 800rpm and see how it goes.

There is also a small vacuum solenoid in the vacuum retard line.
On a cold start that solenoid closes so vacuum retard does not exist. The result is the ignition timing at idle is advanced a bit and that helps raise cold idle speed too.

When the K-jetronic box under the seat opens the vacuum retard solenoid after around 20-45 seconds depending on the year of your car and other variables the ignition timing retards and idle drops noticably all at once.
The aux air valve that bypasses air around the throttle body is closing around the same time but when you hear an abrupt drop in idle thats the timing being retarded.
That is another system to check and see if it's working correctly.

I've also heard that solenoid in the vacuum retard line also closes under boost via the throttle position switch at full throttle so the vacuum advance will become boost retard.

[mooney265]

Thanks for all those recent replies!! I'm going to look at the timing advance/retard points that were just made - - I'll get back with you after I've checked in to them.

[NathanUK]

Shannon, are you saying you have a wideband sensor screwed in to your headers? This is not good for several reasons, you should move the sensor so it is after the turbo. Do a search on sensor locations on the forum for more info.

[mooney265]

Nathan,

We put the sensor on the space provided by B&B. I circled where it is on the pic. Basically, it's located at the connection to the turbo.

Is there a difference as to "right before the turbo" and "right after"? I'll read what you suggested and see...

[NathanUK]

There certainly is, get it moved asap.

[mooney265]

What if I moved it to the Left Pipe right after the muffler? Does it matter that it would only be getting 1/2 of the exhaust?? It shouldn't....