New O2 sensor - car runs worse!

[michaelw]

As the saga goes, I noticed a some black smoke when accellerating. Many suggested O2/head temp sensor. I found my O2 sensor was disconnected so replaced with a new one. Now the car runs worse. After hitting gas taking RPMS up to about 2500 and then letting off, the idle drops way down to 200-300 rpms like it's about to die then works its way back to about 900.
Last night I tried adjusting idle down (it was about 1000rpms) by shorting the circuit under the black cover on the left of the engine bay and turning the idle screw, but did not seem to be able to get it to drop. Did I actually screw it up and drop it too much? Where should I check next? Do I need to reset the DME?

Thanks - Michael 87 Targa

[mod]

Do a search on Fuel Mixture ajustment (not idle adjustment) and that may give you some leads.

[nhromyak]

I would look and see if there is anything else disconnected.

You should be able to set the idle (jumper the round plug on the side of the engine compartment with a regular black relay) to 850 +/- 50 rpm. Then all should be well. If it isn't, look under your MAF (MAP? not sure). See if the hole is drilled out. If it IS, then you will need to have the CO analyzed for a correct setting.

If its not, you may need to get the other sensor(s) checked for connection and working. TDC sensor, and there is another sensor right next to TDC, I forget what it is called.

Good Luck!

1987
1. USA idle speed 800+-40
2. USA idle speed 880+-40** 1987 models with control unit
911 618 111 18, 19 or 20

Making idle adjustments

Engine in perfect running condition

Procedures must be performed in given sequence.

1. Connect CO tester
2. Run engine to operating tempurature
2A. Disconnect O2 sensor plug
3. Check and adjust CO on air flow sensor.
3A. reconnect O2 sensor plug
4. Check idle speed, correcting if necessary. This requires stopping function of the idle volumetric control.
a) jumper pins B and C with a localy made wire.
b) check and adjust control screw (bypass) on throttle housing.
5. remove jumper and check and readjust if required

Things that can cause eratic idle
Ground connections, plug connections
speed sensor
Reference mark sensor
ignition system
air flow sensor
fuel pressure
idle positioner
throttle switch
temp sensor
fuel injectors
intake system leakage

On my 86 3.2 the reference and speed sensors both had failed jacketing on the cables. Bosch # 0 261 210 005 you will need 2 if that is the problem.

The Porsche manual has a very good trouble shooting guide and shows you how to test the above.
Start with simple easy things grounds clean and connected. Did you disconnect something wile changing the O2 sensor etc.
Some tests call for an O-scope but a decent analog one is not that expensive. (the factory manuals will cost more)
Well didn't answer your question but the above may help.
Mavbe someone could scan and e-mail you the manual pages....just a thought.
Chris

[michaelw]

Chris,

Thanks for the exhaustive list of where to check and the factory manual pages would be good. Anybody got them?

Thanks,
MichaelW
87 Carrera