Idle Screw Bottomed Out?

[mooney265]

I just noticed that my idle [rpm] screw is fully bottomed out. Can't turn it any more clockwise...

The car idles at 1,100 rpm. I was going to lower it to around 1k, but can't...

Has this happened to anyone else? What could it be a symptom of? Vacuum Leak?

FYI: When I turn it CCW, my idle rpm increases...

I have a mity-vac, so - what is the best way to use that to check for vacuum leaks?

Thanks in advance!

[9dreizig]

Have you had your AFR's checked?? When I had this problem it was indicative of it running way too rich.. I"d start with that , then go from there.
Oh and yes running rich could be indicative of a vacuum leak

[mooney265]

todd,

I have a wideband o2 with a digital gauge... AFR idle is 12.0 when cold and 13.8 when warm...

I run around town in the high 13's.

My mechanic says it could be a vacuum leak... I've checked the o-rings on both sides of the intercooler; all hoses connected to the intercooler have been changed and are clamped down tight; intake has been re-torqued [wasn't loose, though].

[356-930]

Originally Posted by mooney265

I just noticed that my idle [rpm] screw is fully bottomed out. Can't turn it any more clockwise...

The car idles at 1,100 rpm. I was going to lower it to around 1k, but can't...

Has this happened to anyone else? What could it be a symptom of? Vacuum Leak?

FYI: When I turn it CCW, my idle rpm increases...

I have a mity-vac, so - what is the best way to use that to check for vacuum leaks?

Thanks in advance!

Yes, sign of a vacuum leak.
The idle screw is an air by-pass screw meaning the more you open it (CCW) the more air is shuttled below the butterfly of the throttle body.
Somewhere on this forum is a write up and photo of some handy tools to check for leaks, engine not running using minimal pressure, i.e. 5-psi.
A mighty-vac might be used to check for a leak in the distributor's vac/boost advance diaphragms but not much more.
Lots of vac hoses, intercooler seals, intake block seals etc. to check for the source of a leak.
Good luck.

[9dreizig]

Well for my cars that's running a bit rich, but not too terrible.. The next step is to get yourself a can of carb cleaner and while it's warm and running , start spraying around and if you've got a leak the idle will drop when you get close to the leak.. How are the intake nuts ? they are famous for coming loose.

[mooney265]

Originally Posted by 356-930

Yes, sign of a vacuum leak.
The idle screw is an air by-pass screw meaning the more you open it (CCW) the more air is shuttled below the butterfly of the throttle body.
Somewhere on this forum is a write up and photo of some handy tools to check for leaks, engine not running using minimal pressure, i.e. 5-psi.
A mighty-vac might be used to check for a leak in the distributor's vac/boost advance diaphragms but not much more.
Lots of vac hoses, intercooler seals, intake block seals etc. to check for the source of a leak.
Good luck.

Ok, that makes sense... I'll have have to take both of your's advice and get hunting around with a can of carb cleaner... That stuff's not flammable [if spraying around the turbo cold-side pipes???

[mark houghton]

Uncontrollable high idle alway makes me suspect the AAR being faulty (as in stuck wide open). Have you done the simple diagnostic of pinching the hose to the AAR closed to see if the idle drops? Too much air getting into the intake, either from vacuum leak as mentioned or possibly the AAR.

[Ronnie's.930]

Here is some good reading regarding high idle problems (also a couple of links within this thread):

need help with idle proble <did many many searches with no result

[mooney265]

Originally Posted by mark houghton

Uncontrollable high idle alway makes me suspect the AAR being faulty (as in stuck wide open). Have you done the simple diagnostic of pinching the hose to the AAR closed to see if the idle drops? Too much air getting into the intake, either from vacuum leak as mentioned or possibly the AAR.

funny how you should say that... I just got back from disconnecting and plugging the AAR.

with the idle screw totally bottomed out, it still idles at around 1,100 rpm. On a side note, the cold idle is about 900, now.

I noticed that the idle slowly climbs from 900 to 1,100 as the WUR slowly raises the control pressure [warms up]. my warm AFR of 13.5-ish may be a little low. and, I'm guessing if i lean out the idle mixture, the rpms will climb. but, with the idle screw bottomed out, I won't be able the lower the rpm's...

so, as it leans out, the idle rises. this tells me that "other air" is getting in there...

Q: Is a "boost leak" the same as a "vacuum leak?" In other words, If I find a leak, would this cause both vacuum and boost leakage?

[9dreizig]

[Q: Is a "boost leak" the same as a "vacuum leak?" In other words, If I find a leak, would this cause both vacuum and boost leakage?[/QUOTE]

Pretty much the same... or at least same symptoms

[mooney265]

Originally Posted by 9dreizig

[Q: Is a "boost leak" the same as a "vacuum leak?" In other words, If I find a leak, would this cause both vacuum and boost leakage?

Pretty much the same... or at least same symptoms[/QUOTE]

The reason I asked is that I have no problem with generating boost. I get .95BAR at 3,300 rpm. And it stays thru the rpm band...

so, if i have a vacuum leak, then i could be losing some boost capabilities. So, I can kill 2 with one stone - - Just need to find the leak...

[mark houghton]

I think it's possible to have enough of a leak to cause the high idle, but not appreciably affect boost. Sounds like that may be the case with your issue. Do try squirting carb cleaner around to see if you can isolate it.

I wonder if your decel valve is ruptured or stuck, letting gobs of air in all the time, when it's only supposed to do that under deacelleration with the throttle butterfly closed. It seems you're getting air introduced post-throttle.

Just some thoughts from someone who is far from an expert.

[mooney265]

Originally Posted by mark houghton

I think it's possible to have enough of a leak to cause the high idle, but not appreciably affect boost. Sounds like that may be the case with your issue. Do try squirting carb cleaner around to see if you can isolate it.

I wonder if your decel valve is ruptured or stuck, letting gobs of air in all the time, when it's only supposed to do that under deacelleration with the throttle butterfly closed. It seems you're getting air introduced post-throttle.

Just some thoughts from someone who is far from an expert.

I removed my decel valve last month. Totally gone - - plugged off upper and lower connections. And removed and plugged the vacuum line, too.

Now, maybe I should remove [or bypass] the AAV next to the AAR???? Heck, I've deleted the AAR and DECEL, might as well go for all 3!!

[Ronnie's.930]

A couple of months back, my 930 had similar high idle problems (idle was around 1500 warm and no amount of tightening/closing of the bypass screw would reduce it) - turned out to be the decel valve was bad. I opted to eliminate the valve and all is well . . .

The link(s) I posted previously go into this in detail . . .

R

[Ronnie's.930]

opps - you posted just prior to me !!!!

[s5uewf]

maybe when you put the IC back on after removing the AAR an o ring got pinched.

I once found the o ring between the component with the butterfly valve under the intercooler and that big magnesium pressure chamber was split. No way to inspect it other than to remove the magesium piece. Not as obvious as the o rings on the inlet and outlet of the intercooler itself.

You also may have to vacuum lines coming out of nipples in back of the fuel head, between the firewall and the fuel head (my 1988 does). One goes to the distributor and one goes to the same butterfly valve component, if my memory serves. It's all near the AAR and the decel valve so you may want to double check.

[mooney265]

Originally Posted by s5uewf

maybe when you put the IC back on after removing the AAR an o ring got pinched.

I once found the o ring between the component with the butterfly valve under the intercooler and that big magnesium pressure chamber was split. No way to inspect it other than to remove the magesium piece. Not as obvious as the o rings on the inlet and outlet of the intercooler itself.

You also may have to vacuum lines coming out of nipples in back of the fuel head, between the firewall and the fuel head (my 1988 does). One goes to the distributor and one goes to the same butterfly valve component, if my memory serves. It's all near the AAR and the decel valve so you may want to double check.

Emery,

thanks for the input/advice. I can definitely rule out the o-rings. I've taken off and on the intercooler 6X in the past week. Always grease those o-rings and they're in tip-top shape [just changed them out a couple months ago - - just because...]

i'll get to looking "behind" the fuel head to check out the vacuum lines back there.

i can't seem to find any evidence of anyone removing the AAV [not the AAR] on this forum... i'm calling the AAV the device that looks like a flying saucer that is located on the PS of the fuel head - - anyone?

[WinRice]

For the vacumn leak to effect the idle speed it has to be between the throttle plate and the engine, since all the idle screw does is bypass the throttle plate.

So check all places air could leak in after the throttle plate, AAV, vacumn lines, gaskets, etc. Even cracked injector blocks.

[JFairman]

You ought to check your ignition timing at idle. If it's a little more advanced than the stock setting that will raise idle a few hundred rpms too. Vacuum retard if your car has it may not be working anymore.

30 year old origonal phenolic injector blocks are often cracked from age and stress and that could be a vacuum leak that will raise idle.

[mooney265]

Update:

As I had previously stated, I disconnected the AAR and drove the car this morning. It drove nicely [still 1.1k rpm idle]. It just didn't have a high idle at initial start.

I got home, did a little bbq and let the car cool off. with a belly full of beef, I got back to work on the car.

started by removing the AAV [flying saucer] on the passenger side. so, with the intercooler plugged up [AAR and AAV lines] and the AAV deleted, I attempted to start the engine. It started [like normal] and after running 30-seconds, I shut it off.

Here's where it gets a little spooky: when I turned off the ignition, the engine remained running for about 2-seconds and shut down like a diesel?????

That got me a little nervous, so I got back in the engine bay and began second guessing my work... I began by questioning the removal of the AAR plug. I figured the plug needed to be plugged in for the CIS to work. So I replaced the AAR simply so I could plug it back in...

With the AAR replaced and plugged in, I attempted to start the engine. This time, it started right up and began to idle at about 2k [as expected with the AAR]. But, as soon as the idle went up, it simply "ran out of fuel or air" and stalled. FYI: this engine never stalls!!

So, then I got to thinking about the AAV. The car ran fine with the AAR removed and the AAV hooked up. Now, with the AAV removed, the car isn't running. So, back on with the AAV. In doing so, I got a chance to change the vacuum line running to the AAV.

Then, I ran into a problem: I couldn't remember which way the vacuum lines were hooked to the THERMO TIME SWITCH. I have a workshop manual and it shows the center vacuum line goes to vacuum and the outside vacuum line goes to the AAV.

Q: Is this correct?

Anyway, I think I flooded the car and fouled the plugs... So, i'm giving it a rest and will attempt to restart shortly...