Engine - Idle Adjustment Procedure
83porsche03Subject
Engine
Part Identifier 1001
Applies To 911 CARRERA
1984
Group
10
Key Points
Idle adjustment procedure and preliminary diagnostic guide for engine performance problems
C
Number
83-10
December 30, 1983
Idle adjustment procedure
Engine oil temperature must be approximately 90~C (194~F).
Intake air temperature must be approximately 15 to 35~C (59 to 95~F).
CO tester connected in front of catalytic converter
- disconnect oxygen sensor
- check/adjust CO% at idle
^ Specifications = 0.6 to 1.0%
- reconnect oxygen sensor
- bridge terminals B and C on the test connection receptacle (see illustration). This makes the idle stabilizer inoperative.
- check/adjust idle RPM
^ Specifications = 800 +/- 20 RPM
Adjustments are made with the throttle housing adjustment screw.
- remove bridge from test receptacle.
- recheck CO% and idle RPM.
- remove CO probe and close catalytic converter connection.
Note
For accurate adjustments, it is absolutely essential to follow the prescribed sequence.
Diagnosing engine performance problems
Incorrect idle RPM
- RPM higher than 820: The deceleration fuel shut off valve is activated, causing idle surge, jerking in stop and go traffic.
- RPM lower than 780: May cause stalling at idle when operating A/C, hesitation upon acceleration.
Incorrect CO adjustment
- CO valve greater than 1%: May cause idle surge after cold start.
- CO valve lower than 0.6%: Idle unstable, possible hesitation upon acceleration.
Temperature Sensor II, responsible for correct warmup enrichment (located in left cylinder head by number 3 cylinder).
Temperature Resistance values
10~C (50~F) 3.3 to 4.1 K Ohms
20~C (68~F) 2.2 to 2.8 K Ohms
40~C (104~F) 1.0 to 1.3 K Ohms
80~C (176~F) 290 to 350 Ohms
100~C (212~F) 160 to 210 Ohms
- if sensor is disconnected (resistance = infinity) the engine will run too rich and stall at idle
- if sensor is shorted to ground (resistance = 0 Ohms) the engine will experience difficulties in cold start and warm-up.
Engine speed sensor and reference mark
^ Specification: Distance for engine speed sensor to flywheel = 0.8 +/- 0.3 mm.
- at a distance of approximately 2 mm: Longer cranking time, more starts necessary, will not start at lower temperatures. During warm-up engine will run normally; at operating temperature will idle higher than normal (see incorrect idle RPM).
- at a distance of approximately 3 mm: The engine experiences ignition misses and hesitation upon acceleration. Due to heat expansion, engine may quit running for short periods at a time.
Fuel return hose
- if the fuel return hose is kinked or blocked, fuel pressure will rise causing rich running and stalling at idle.
Note
If CO% cannot be adjusted to specifications or engine surges at idle when cold or under partial load, test fuel pressure.
^ Specifications = 2 bar at idle (vacuum hose connected)
Spark plugs
- wear limit for electrode gap = 1.3 mm
Hot start problems
At operating temperature, the fuel pressure drop is approximately 0.5 bar in 30 minutes. If pressure drop exceeds specifications, check the following:
- pressure regulator for internal leak. Test by closing off fuel return hose.
- check valve in fuel pump for internal leak. Test by closing off fuel pressure hose.
- injectors for internal leaks. Test by closing off both pressure and return hoses.
Acceleration linkage adjustment
- the long rod on the transmission relay lever must have a clearance of 0.5 to 1.0 mm for proper operation of the idle microswitch.
Idle microswitch
Inoperative (open) switch will produce an increased idle (approximately 1100 RPM) and the ignition timing will be advanced. The following may also occur:
- when decelerating from over 5000 to under 4000 RPM, the engine will hesitate upon re-acceleration.
- with a cold engine, acceleration delayed by approximately 1~ of throttle opening; engine surges.