i have a porsche 911 3.2 1987 just bought this car and idle would sometimes hold and other times the engine would switch off i opened the idle air control valve today and found a piece of pipe inside i presuem this was used to lower the idle speed by restricting the air what a bodge
anyway i have removed it and cleaned out the idle air control valve problem is the car now idles at 1200 rpm and after a short while the revs drop and increase any ideas what this could be

 

Check the vacuum lines. There are a couple that connect behind the throttle body and also run to fuel pressure regulators on the fuel lines on each side of the engine. Also check the idle switch at left rear of throttle body.

Good Luck
Andrew

 

what is an idle switch is it different to the idle air control valve

 

The idle switch is a microswitch that tells the engine control unit that the throttle is closed and the engne is idling. It is acutated by a tab on the throttle linkage at the throttle body that presses the switch. Sometimes the switch just needs to be adjusted so that the switch contact is closed when the throttle is closed. Occationally the switch goes bad (like mine did).

With the engine off, if you pull slightly on the linkage where the cable attaches you can hear a small click if it adjusted correctly. Or better yet, disconnect the connector from the wiring harness on the right side of the throttle body and use an ohm meter to check.

Andrew

 

could you please explain how i check with the ohm meter do i measeure from the loom side and what figures should i be getting the switch does click as you say
i did find tday when the idle air control valve was disconnected the car still showed the same symptoms if i spray carb cleaner into the idle air control valve top pipe whilst the car is running the revs wil automatically start rising

 

Mixture.

 

"Or better yet, disconnect the connector from the wiring harness on the right side of the throttle body and use an ohm meter to check." - AJ88CAB -

He's correct. The idle switch is the most common idle problem source. You can
check it by connecting an ohmmeter from pin 2 to pin 5 on the DME connector.
This test should measure about zero ohms with the throttle at rest. The switch
opens when the throttle pedal is slightly depressed.

 

ok had a look at the throttle position sensor switch i left it connected it only has two wires going to it ie brown and white when i conneected the multimeter to it it read -6.0ohms and on pressing throttle when fully open i got -11.6 these reading seem odd am i doing something wrong
sorry forgot to ask where is the dme connector