deviation in idle

MAD4PORSCHE · 05-09-2003, 05:29 PM

The idle on my 81 SC is set to approximately 1100RPM. After the engine is warm, if setting at idle for more than 30 seconds it starts to deviate between 1050 and 1150RPM. If I remove the oil cap, the engine idles at exactly 1200RPM. Any ideas?

Mark

Doug Zielke · 05-09-2003, 05:56 PM

Is your O2 sensor still connected at the plug in the left side of engine compartment?

jason2guy · 05-09-2003, 06:31 PM

id say 1100 is too high. set it at 900 warm. then for the idle prob get a mixture wrench (3mm allen) and either lean it out or richen it up untill it just stops hunting. its probably a little lean, so turn it clockwise a tad

jbripps · jbripps's Garage

Mine idles right around 750/800 when warm. Not sure if that helps, but has been that way since I got it 2 years ago. Sometimes surges at startup in the cold and goes b/w 1000-1500 for 30 seconds or so.

regards,

MAD4PORSCHE · 05-10-2003, 01:48 AM

Hello Doug:

I removed the 02 sensor a couple of years ago and back-dated the exhaust during the winter. SSI with 2-in 1-out muffler.

Mark

05-10-2003, 05:15 AM

May be running a littl rich. I had the same prob. Leaned it and it settled out.

stlrj · 05-12-2003, 01:38 AM

Ditto that. It sounds like a rich hunt at idle to me too.

Joe

targa80 · targa80's Garage

Quote:

If I remove the oil cap, the engine idles at exactly 1200RPM. Any ideas?

I believe that normal idle should be 950~1000, removing oil filler cap the idle should drop to 750 ~ 800 or just above stalling. Sounds like you have some other issues, I.E. no O2 sensor so no continuous fine adjustment of fuel mixture. Does adding air through the oil filler to an over rich mixture increase idle ? Does adding air through the oil filler to a normal or lean mixture decrease idle?

ruf-porsche · ruf-porsche's Garage

If the sensor plate remain at the same location, I would think that adding additional air through the oil filler will increase the idle, however, because the sensor plate change with respect to engine speed because of the flow of air through the plate I don't think you can isolate the effect of the sensor plate out of the equation.

Since my car is not modified (other than a Porsche CD-2 stereo) it still have the 02 sensor and all the pollution equipment on it the idle drops when I open the oil filler cap, but not to the point of stalling. My car is not burning rich or lean according to the spark plugs color.

Porsche spends millions of dollars developing products that the end user will be please with and conform to all the rules and regulations of the area were the product is sold.

I don't understand the reasoning behind changing the parameters of the system if it just cause more problems. Removing the 02 sensor may(?) make the car run better, but eventually the cat converter will suffer. It's interesting to note that some cat bypass pipe is fitted to accept an 02 sensor.

I'm of the school if it ain't broke don't` mess with it.