Whats happening during 'cold idle' in a 964

[einreb]

(EDIT this is a crosspost from Rennlist... I'll assemble and repost the results)

I'm looking to try to diagnose the cold idle problem (idle jumps, wants to die for first 90 seconds and then perfect when warm) on the 964 3.6 transplant in my '88. I've read a bunch of similar issues on this 964 board and want to assemble a thorough 'checklist' of things to go through.

I'm under the assumption that the O2 sensor is out of the loop when cold.

Done:
I checked the CHT sensor resistance when cold.
I checked that the idle microswitch is engaging.
I pulled and checked the MAF box. It was quite clean, but I don't know if that means its working correctly.

To do:
Check for vacuum leaks.
Check/clean the ISV

Questions:

• Is there a diagram of the vacuum lines posted anywhere? Some of the lines for this conversion have been capped, and I don't want to assume that it was done correctly.
• Is there a way to check for the proper opperation for each of the electro/mechanical devices involved? i.e. jumper the plug for the microswitch to take that out. resistor for the CHT.
• Can I measure the 'output' of the MAF?
• Other than 'cleaning' the ISV, can it be checked for propper operation? Powered up?
• Anything else I'm missing? carbon canister?

Since there are lots of threads on this subject, but few technical details, I'd like to try be able to compose a checklist and methodology for determining the problem for folks (as well as figuring mine out!)

Thanks,

Bernie

[Bill Verburg]

There is some info and pics re 964 t/p vacuum lines here

My first guess would be the ISV

[ischmitz]

Bernie, Once you have checked for the ususal it's because of the lighter flywheel in the conversion: The response of the DME is not fast engough, idle oscilates and the engine even dies when cold. Fixes are to install a chip with idle correction code and to adjust the AFM air bypass. Check here for details. http://sswl.di.com/~ingo/Chipping.htm
Cheers,
Ingo

[einreb]

Ingo and Bill... Thanks for the feedback.

I pulled the ISV today and hit it with carb cleaner. A 12v source clicked it right over that seems ok.

To my amazement... the 'air muffler' that connects between the ISV and intake manifold had a huge crack in it at a seam. I'm assuming that could cause a strange vacuum issue I'm going to hit it with some DOW 730 in the short term to see if that helps things. Unfortunately, Ive got some other things apart and am waiting on a muffler swap, so I can really test it out till later in the week.

Bill, those vacuum line diagrams almost make me more confused... the top one on mine (to the brake booster?) is capped. i assume thats ok. I also have a line that comes out of the carbon canister to a 3 way split. one goes to the vacuum system and the other is plugged. I'll try to get a pic.

Ingo, I have a Cyntex chip that is supposedly tuned for a LWF. would yours be different? (other than the nice switch option)

Thanks guys!

-bernie

[ischmitz]

Bernie,

The crack will for sure mess with your idle as it is a huge vacuum leak intruducing unmetered air. Good find. Let us know once you have it back together.

The NBD chip won't be much different but as you said it does have the additional benefit of being able to switch between stock and performance.

Good luck,
ingo

[einreb]

ingo, thanks.

while i have your attention.... one other 'post swap' issue i have is a weird buzz from the tack at certain rpm's. my initial thought was voltage regulator, but that causes a bouncy tach, not buzzing. any thoughts?come on man... diagnose my weird noise problem from 2000 miles away!

-bernie

[ischmitz]

buzzz, err..... it's gotta be the flux capacitor

Seriously, I don't know. Are you saying the tachometer makes noise??

[einreb]

whoops tack != tach.

yup. i'm pretty damn sure its the tach. i guess when i get the car rolling again later in the week, i could disconnect it to be sure thats it. its weird for sure. i guess i need to check some diagrams and look into grounds. not sure what else it could be.

the DOW 730 is now drying on the 'air muffler'. fortunately a good buddy just picked some up at $75 a tube, so I got to 'borrow' some. man thats some mean stuff.

[einreb]

I'll be damned. The cold hunting idle went away!

It appears to idle a bit high when warm at times, but I'm going to drive it a bit to see how things settle out. Is the "Resetting the computer" a myth? i.e. unplug the battery and then reconnect and go for a "spirited drive"?

I also now have full WOT. Holy crap. I was missing about 1/2" of throw on the patrick conversion cable.

I still have the exhaust to sort out (hopefully tomorrow), the A/C to hook back up and charge and some other minor stuff, but its getting close to being done... as done as this sort of thing ever is.

-bernie

[einreb]

Another 'data point'. Fixing the vacuum leak took care of the cold idle, but then it would stall when warm! I've got the LWF and rs clutch package.

I didn't believe it would work, but doing a DME reset seems to have taken care of the stalling problem. I suspect the car had 'learned' based on unmetered air entering the system. With that not happening, it ran poorly. Now, its quite pleasant to drive, i can certainly tell the difference with the LWF and clutch, but its not at all unpleasant. On the contrary... its quite nice.