185318

Greetings,

I think I finally found the problem with my cold starts and erratic idleing. Looks like the temp II sensor is shot. My questions are: this measures water temperature and turns cooling fans on at a specific temp?...and is it okay to drive the car with it unplugged for a couple of days until I can get a new one?

Thanks!

MikeN

It's the sensor that sends data to the LH controller if I'm not mistaken. Let's the controller know what temp the engine coolant is and adjusts many running conditions. If it were me I would not drive without a good one, but probably won't hurt anything........

185318

Mike,

Thanks for the info. I think you're right. Even though it starts a whole lot easier and the wild idle fluctuations are gone with the sensor unplugged, I can wait a couple of days for the new one.

Thanks again

Jim bailey - 928 International

it tells the Lh fuel brain that the engine is cold , add more fuel and tells the spark brain the same so it advances the ignition timing by 3 degrees .

John Speake

If the car runs much better with it connected, the car has a serious problem, and it's probably not the temp 2 sensor, which usuallly fail open circuit anyway.

You can easily check if its OK by resistance from each of the pins in turn to ground. A couple of thousand ohms at ambient temp.

As Jim says, all you have done is to artifically enrichen the mixture, which is hiding the true fault

aaron3

John,

"If the car runs much better with it connected"... do you mean disconnected?

What might be a 'serious problem' in this case. I'm just interested, I've been having some idle problems lately and I'd like to understand this thread.

185318

john,

The car doesn't necessarily run better, but starts on 1st turn and idle is no longer fluctuating wildly, with the temp sensor unplugged. I plan on investing in an ohm meter tomorrow and testing resistance. Could the sensor be getting voltage but still be bad? When I connect it, car has a VERY hard time starting. When DISconnected, car starts 1st time. This leads me to believe that there is some voltage, but that the sensor is not doing what it needs to do.

John Speake

Mark,
yes, my apologies for my silly typo. I meant disconnected. By a "serious problem" I meant something that gives a weak mixture. i.e. air leak intio the inlet system - split hose, gasket, etc. Or a MAF that is well aged and hence running weak.

The idle stabilisation system is quite complex, but it does give warning of various problems. The idle stabiliser is essentially a motorised valve. It bleeds air into the intake system in a controlled way in order to keep the idle rpm at the correct speed. This is all controlled by the LH ECU But it has a limited range of operation. So if there is a bad air leak into the inlet, then the idle stabiliser loop just can't cope, and the idle will be erratic as the loop "hunts" around trying to reach equilibrium.

Also, if the idle switch on the throttle body isn't working, then the car won't idle properly. Bad grounds can also cause a problem. A faulty LH ECU obviously can also cause a problem.

The reason that sometimes a car won't idle cold, bit will when warmed up is that when cold, the O2 loop is disabled, and any MAF ageing is not well compensated. When the engine warms up, and the O2 loop is active, then it can compensate better for the MAF being weak.

Hope this helps.

185318 - temp sensor2 is two independant temp dependant resistors in one housing. They both are connected at one end to the engine block. each pin should measure approx 3,000 ohms to chassis (ground) at ambient temp. And approx 300 ohms with the engine at normal temp.

When you disconnect the temp2 sensor, you are fooling the ECU to make the mixture very rich, as it think the engine temp is 40 below zero ! This suggests that the car has a very weak mixture when cold.

Rufus Sanders

Don't forget what Jim B said. It sends input to control mixture and spark . You can get a temp 2 sensor at NAPA easily, put it in and see if the problems persist. I had starting issues last year and I thought it was the temp 2, but it was totally ignition related.

And while you're at NAPA, get a dgital multi-meter. You can't do a thing on these cars without one.- Ruf

glenn faken

after i read the reply from john i thought well i might as well check my temp sensor. the sensor was good but the conector had some kind of goo on it. it wasn't a weather pack type grease. it was an elastic type of material that had leeched its way from the top of the connector down the wire and into the body of the conector around the metal tab of the sensor.

the connector is sealed on top with a substance that apparently in my case was affected by something that made it ooze down and interfer with the connection.

so if your checking your sensor look under the connector to verify it is clean

glenn

John Speake

Hi Glenn,
Yes, this connector "goo" problem is quite common, on the Bosch connectors in the engine bay where they get very hot. It's a common issue with the 3 pin knock sensor connectors too. The problem appears to be the heatshrink sleeve that Bosch/Porsche used on the wires into the connector (inside the rubber boot).

The only fix is the replace the connector. There is usually enough spare lead to enable this. The Bosch connectors are readily available.