dr bob

Used the car yesterday to run errands and the like. We're getting to the end of driving season here so I'm trying to get a good dose of fun before she goes on the lift for a couple projects then into hibernation.

Leaving the last errand stop, at the end of the parking lot waiting for a break in traffic... the engine died. Restarted OK, but anything out of the ordinary like that gets my attention. Drove OK until I slowed for a roundabout, then started some pretty significant surging, between normal idle speed and staying just north of stalling. Into neutral and blip the throttle, and fine after a second. Off the pedal, and surging and thinking of stalling again. I was just a couple miles from home so decided to nurse it to the garage. Confirmed in the driveway that it still surges at idle, and that it would restart.

This morning I decided to do a slow loop of the neighborhood and see if it happened again. While cold, no surging. By the time coolant came up close to temperature, it started again. Turn back towards the barn, with symptoms same as yesterday. But coolant temperature seems to be part of the package of symptoms. Grab the WSM's and find the test protocol and test values for the Temp Sensor II, which supports both LH and EZK functions. It tests fine from both the LH and EZK connectors. Scratches head...

The MAF is original, and I keep threatening to have it redone prophylactically. Maybe now's the time... So out comes the MAF. Visual once-over. Wires inside all intact. I noticed that pin 1 in the MAF has a little bit of scrudge on the pin. With a small pick and contact scraper, it comes off with a little work. It's almost like a bit of rubber cement. In the mating connector on the harness, there's a similar buildup of this stuff in the pin 1 female side. This is more fun, since it's in the car and I don't have the benefit of working under a bright magnifier. Still managed to get the stuff out of the connector. Reassembled, car starts up just fine as it did before. So I let it warm up to temp with engine idling, waiting to see when the surging would start. It didn't. Car runs fine again.

So how did a rubber cement-like substance find its way into just one pin of the connector? Will it come back to haunt me once again? Will Ctutch Cargo find his way out of the tiny airless closet? Tune in next week....

Fun stuff. An hour of fun figuring it all out. I got to pull out the fender covers and use them. Still scratching my head because it's a really odd cause. And there's no sign of a source for the scrudge on the connector pin. Last time that connector was apart was to test-loan the MAF for another car at a local shop that wasn't running right. Did that stuff come from the other car? Still scratching my head. Where there used to be hair.

MainePorsche

Any sign of plastic melt of the harness ?

As expected, quick algorithmic approach to the issue along with resolution.
Would we have expected anything but...

Adk46

The Cubs win the World Series, and scrudge is found in the most meticulously-kept car on the planet. Something is distorting the space-time fabric of the universe. My computer is even off an entire hour this morning.

dr bob

Nothing in the harness or connector is showing anything remotely like what was fouling the connection. The boot around the connector is torn, so that will be replaced after I disassemble and completely sanitize the connector itself. Otherwise everything there is pretty spotless.

There's a spatter of something unrelated in the rear of the valley, and I'll get that when I pull the MAF again for refurb and the connector boot replacement.

I'm wondering if the loan-out for testing is somehow related. A local non-specialty shop had a 928 that was suffering from either MAF or LH failure, so I allowed them to borrow the MAF from my car for a quick test. I wonder if his car had something in the connector and some of it moved with my MAF when it was put back. I know they replaced their with one from Rich Andrade at Elektronic Repair. Perhaps that owner had the same symptom?

My car is hardly the most meticulously-kept car on the planet, but thanks for that thought. I do try to do everything on a proactive rather than reactive basis, mostly so I can eliminate the need for extensive diagnostics and troubleshooting. So this little session was certainly a rare exception.

Process:
-- On the way home the first time with idle surging, I jammed hard on the pedal a couple times and got good responses for those few seconds, trying to rule out fuel pressure and ignition as possible causes. Either would be worse under load than at idle.

-- The IAC was replaced five years or so ago as part of a full intake refresh, so that moved down the list some but not off of it. Physically checking it requires intake removal, so it moved a few more steps lower on the list.

-- The dash display of instant fuel economy went to 90MPG on trailing throttle with engine over 1500 RPM, so the throttle position switch is obviously closing. The throttle switch closes to enable the Idle Air Controller, so confirming the switch that way saves another troubleshooting step. Doing just a few things quickly and dramatically narrows the possible causes list.

-- The only-when-warm symptom was a little confusing, steering me towards the temp sensors, so they were checked out first.

-- Then the MAF, which is still original at 110k, was next. Usually a visual inspection won't tell you about wear-related failure modes, but in this case it confirmed at least that the sensor wire and the heater are still intact. That's hardly definitive though, so I was proceeding based on the miles and symptoms. It was only when I took a very close look at the connections that I saw the stuff in pin 1. Cleaned that out, and moved back to the engine bay for another look at the harness connector. Pin 6 in the connector isn't used so it isn't installed at all. After my initial enthusiasm for finding the missing pin connector, it took just a tiny bit longer to realize that the missing part is not pin one. Then cleaning that one connection was less fun. But the result is satisfactory for now.

MainePorsche

Bunch of non 928 guys leaning down and back to plug the MAF in for testing, and you think the soilage is not related...

dr bob

I was there the whole time. The engine was hot, so the tech had gloves on for that part. He knew what he was doing as far as the R&R, since he'd already R&R'd the DUFO one on the other car. Unless the connector on the other car was contaminated, there was no real opportunity for the tech to screw it up. Plus the car has driven fine all summer since that exercise.

The only available flow path for stuff into the connector, once assembled, is past the pins on the wire harness side, through the little holes the pins pass through. Not much room, but some.

That harness connector was assembled with a large piece of heat-shrink around the lip where the boot sits. Then the boot fits over that. I'm guessing that the shrink sleeve is there to limit the bend radius on the wires inside the boot.