napaul

Before anything else i have read the many posts on what will be my question but still confused.

I drove my car to work today. for the last week i have been having erratic idle issues where it will idle at stand still from 900 rpm and drop to 700rpm and then back up i guess hunt for idle would be best description. so i checked and did not have the tsb done for harness on airbox so i did that, i also removed the isv and cleaned thoroughly. Now today i was driving home and at the lights when i came to a stop i noticed idle was down near 500 or first tick on tachometer and dropping to the point i felt i needed to keep giving it gas to stop it from stalling. My check engine light came on also but was not in a spot i could stop so i drove it gingerly home and can only describe it as it did not drive normal almost like it was down on power. I got home hooked up a scan tool and the only fault it showed was knock sensor 2.cleared it and started car it was idling at 850-900 rpm.Although the fault for knock sensor shortly returned upon reving it.

here are my observation when durametric scan tool was hooked up and set to actual values on motronic. voltage was idle at 13.2v never climbled when given gas but will confirm with meter at battery posts to see if alternator is acting up,engine temp was reading 117.2,o2 sensor was reading .
i realize some info is not useful but i do not know what info would be of use.
one last thing i ma down to 1/4 tank of fuel and last fill was 89 octane i know dumb thing to do.I will assume that is what has set off the knock sensor.upon inspection of engine bay i notice the rubber boot cover for the hall sensor is torn open or cracked open as was the rubber cover on the harness that i did the tsb on with the zip tie. could all thios be due to my stupidity with low octane fuel? would bad coils cause this or show any faults on scan tool?

napaul

ok i really suspect my alternator to be faulty.i hooked a mmultimeter across battery terminals.with engine at idle it read 13.2v and with my son in car raising the rpm it does raise the voltage past 13.3.I took out adrian book and in it he states faulty regulator can cause engine to cut off unexpectedly and stall.He also states to check if diodes are failing which will be indicated by ac voltage i should not have more tham 300mv at battery terminals when engine running.So i hooked up meter and show 0.066v ac when engine at idle. Does this look like a bad alternator cause when the engine was rebuilt at elegant motors he told me he put in a new rebuilt alternator?

carlskisWP

13.2 v does seem too low for alt output. Mine is 13.65 v and i thought that was too low based on info in Adrian S's book, but I found some other info on this forum that 13.6 v can be normal alt output. Given the electrical demands the 964s have I wouldn't be surprised if this would cause idle problems. You could swap your battery out with a fully charged one and see if that changes anything. Also sounds like you need a new knock sensor.

stinkydog

I had a bad coil a couple months back. (and strangely, the other coil was good, but the wire to the distributor was bad). the problem really didn't show itself until I performed a valve adjustment and did some other engine maintenance.... somewhere along the line of jiggling wires around and disconnecting stuff, the problems really manifested.

To answer your question - no, the Scantool didn't show those faults - other than an intermittent drop in RPM. All of the ECM inputs, actual values, and function tests worked perfectly.

Vandit

My alternator was charging around 13.3v at idle and wasn't causing any problems. I had it out of the car, so I proactively had it rebuilt and now it charges about 14.4v at idle.

napaul

well since my last post i had a chance to fiddle with it.i started off my disconnecting the battery overnight. Next day i plugged battery in and started it up and let idle for approx 20 min till it got to operating temp making sure not to touch gas just let idle. While it was doing this i sprayed a little carb cleaner on idle microswitch and cleaned off. I am happy to report since doing this i have not had any issues with hunting idle or drop off. However just as preventitive maintance i ordered a new micro switch as i do not know if this one has ever been changed and for $70 from porsche i won't whine to much over the cost. The only other change is i filled up with good 91octane fuel. I can't pinpoint which one resolved the issue but knock on wood it doesn't return. Happy mothers day fellas !and don't forget to give momma a big kissy.....