Idle Air Controller too low
 

1986 911 3.2 us spec. No cat. Sport exhaust.

Adjusting the baseline idle I use the jumper wire, set engine speed to 850, shut car off, disconnect DME (or not) and pull the jumper wire, Start the car again and now instead of 850 or 800 rpm it is maybe 550 rpm. Cleaned MAF. It is clearly working, installed in the correct direction, buzzing (vibrating) with key on engine off.

So for the time being I have left the jumper wire in there. It seems to be happy. Suggestions? Thoughts? Is my DME hating life?

Thanks!

Andrew

You need to set CO levels, make sure everything else is tight no air leaks and plug gaps good, it’s s matter of tweaking idle and using a wide band O2 sensor to adjust.
I have used a good multi meter on the 02 sender but it’s not very accurate I think it should dither around .6 V

Forget the jumper, just set the idle bypass to where you want your idle and you're done. The jumper method is only there to intimidate you into believing you need to take it to a qualified shop. How else would they stay in business?

Cheers,
Joe
87 Carrera

The idle control valves stick sometimes. You can clean it out by spraying electrical part cleaner into the two ports.

You can also take it off the car and try cycling it using a 9v battery. Just very briefly touch a test lead to the pin. Look at the wire diagram to confirm, but if i recall the middle pin is the ground. The two outter pins will open or close the valve with 9v applied.

It sounds like your doing things right, so i would suspect the valve. Buzzing does not necessarily mean it functions, the original valve on my '88 would intermittently stop working when 'tapped' with my hand while bench testing. It was likely doing the same on bumpy roads.

CO adjustment should be part of setting your idle but its not required.

(1) Hot idle, pull O2 sensor wire and adjust CO at AFM to 14.7 afr using a wideband.
(2) Reconnect O2 sensor.
1. Hot idle, disable ISV at test port in engine compartment
2. Adjust idle bypass screw to desired idle
3. Remove jumper at test port. The idle should not change at all.

Because when you have been fighting a problem this long you just throw money at it and it will go away... (at least that is what I learned from Reagan)
Cleaned IAC
No change
Replaced IAC
No Change
3d printed a MAF inlet blocking plate to actually seal that part of the intake system. Smoked the intake, found 2 minuscule leaks, fixed them... no change.

At this point the idle is fairly constant (a little lumpy) at 500RPM.
Pull the oil fill cap and it dies.

I am sure I am missing something simple still. Is there a good way to check to make sure all the cylinders are actually firing at idle? Temp at the exhaust pipes? (individually pulling the power to the injectors or the spark plug wires yielded no change in idle)

Anyone else in El Paso that is really bored, in need of a challenge and willing to poke at this problem in person?

Andrew

Update!
Cylinder number 4 is having issues. The injector seems to be dumping fuel which ate away at the spacer.

Does anyone have ideas on how to disassemble and check the injectors.

Andrew

Does that mean you now have a vacuum leak?

Usually the injectors are removed and sent out to have cleaned and tested. Good time to renew all the intake manifold gaskets and spacers. While you have them off do the leaky triangle behind the intake plenum, oil pressure switch crankcase breather,and the thermostat o rings. Some will recommend to pull engine and if you have the space go ahead. beware of the slippery slope or you may not drive it for awhile!

We passed the slippery slope (or as someone else here calls it the: while-you-are-in-there-itius) after we did:
front wheel bearings
all brake hoses
new solid rear brake lines
new front condensor
all new ac lines
full rebuild on transmission
new clutch
new flywheel
removed whole motor again to install a new ring gear
removed while motor a third time to remove the wevo gate shift dongle (machined wrong!)
new heater boxes
new rear wheel bearings
new carpets
new shifter bushings
new vacuum lines
new thermal switch (930-207-231-00)
new fuel filter
new cap
new rotor
new plug wires
new plugs
new air box
new fuel lines


I did replace the intake gaskets and should have done the spacers (while I was in there!!)

do you have part numbers on the triangle behind the intake?

Found oil pressure switch: 911606-230-00
oil thermostat o-ring: 999-701-053-50
for the crank case breather is that part number 930-207-227-00

and yes, cylinder number 4 has a pretty bad air leak (and fuel leak) now.

Thanks for all your help!!

Andrew

Today I replaced the:
Left CV axle
all of the intake gaskets and risers (it literally never occurred to me until a few days ago to replace the risers too)
the boot connecting the two intake halves
the ball bearing in the fuel pressure tester port (don't ask)
air box
hoses connecting IAC
And I machined the bottom of the intake to be perfectly flat and square
And I cleaned every inch of the intake
And really cleaned the questionable injector. I think a piece of FOD got lodged and did what FOD does best

Results:
Holy cow! The new air box is so much tighter then the old one!
but most importantly... I now have no air leaks and a near perfect air fuel mixture!

HOWEVER...
The idle is ok. It took a lot of messing with but I think I have it mostly reliably idling now. The computer is dropping the idle quite substantially (250+ rpm) when I pull the bypass wire.

More worry some is that the car is not happy under light throttle at speeds over 40. No clue on that one.
Any thoughts on where I should start first?
I am almost running out of parts to replace!

Andrew