Ugly astham like idle

Hey Wally, a couple of questions

wallyp;17338 wrote: 1) Find the Temp II sensor on the top front of the engine. There are two different sensors in the housing, one for injection, one for ignition.
2) Check the electrical resistance from each pin to engine ground (earth). The resistance at 15-30C should be 1.4 to 3.6 kOhms (note the "k"). The resistance at 80C should be 250 to 390 Ohms.
SHOULD THE READINGS NOT MATCH, replace sensor?

3) Remove the large connector on the LH ECU. Determine the pin numbers. Check the resistance between pins 3 and 5. With the throttle closed, there should be close to zero Ohms; with the throttle opened a small amount, there should be infinite Ohms (open circuit).
WHAT DO I LOOK FOR IF THIS TEST DOESNT MATCH?

4) Locate the Idle Speed Control connector on the cross-bar at the top front of the engine. There are three pins in the connector. Make a jumper to connect the pins located at one o'clock and six o'clock. This kills the idle speed control. With the engine fully warmed up and the jumper installed, adjust the idle speed to 680-700 RPM. The idle speed adjustment is on the throttle housing, down between the first and second manifold tubes on the right side of the engine (left as you are facing it). Remove the jumper.

besides Wally's advice, look carefully for vacuum leaks in the system. This could cuase the issue too.

thanks ed

It is not important that the resistance values for the two sensors match, just that both are within spec.

If either of the resistance readings is incorrect, the idle switch on the throttle body (or the throttle body connector or the wire between the throttle body and the ECU) is faulty or maladjusted. The idle switch must be closed at idle, open otherwise.

Just following up... as our problems were similar & I thought you might like to hear what my resolutions were for my 1984 928 S (US) L-Jet...


Eleonore's initial woes were due to, yep, Temp II. Once that was replaced (and timing more properly adjusted than I could at that time), she was running very nicely 750 or 800 RPMs (can't remember which) at idle... solid (then & now). And solid operation, too (now). I had replaced a few key relays en route too (Fuel Pump, Fuel Injection, Starter, etc.)- keeping good-looking old ones on-hand as spares.

Also addressed during her initial visit (under my ownership) to a Porsche shop (Motor Werkes here in Honolulu)- the cause of a fuel leak was found to be a a single brittle hose in the rear (not sure which one though... but I can check my records).

Afterwards, a third issue popped up (would start when cold, would stall when warm; recovered just fine initially and then would not start at all)- which turned out to be the ignition coil which is now a new Bosche. Again, starting & running very well.

Ele has been running just fine since. That said, I decided to start moving forward with some of the projects that definitely need doing- the first big one is a CE Panel refresh- which is sitting next to me and about to go back in. I Dremeled & DeoxIT-ized ALL contacts, checked for proper fuses (all ceramic now), relays and documented, well everything. I'm hoping the CE Panel refresh might help some of Ele's intermittent electrical issues, such as:

-intermittent fan/blower function (regular & AC)
-intermittent speedo & odo/trip odo combo- but working fine... when, um, working
-dim pod & dash lights (will be doing POD refresh too)
-jumpiness of instruments (voltmeter & other gauges) when random items activated (like turn signals, as one example). (Will be cleaning all ground contacts too, including 14-pin connector.)

In working on the CE Panel, it seems I still have a few original (as in from West Germany) relays. Not new(-sh), but obviously showing a little wear, but contacts and function were fine... will find out if everything still is in a moment!


-tom