Idle question?
12-02-2004, 02:03 AM
#1
Burning Brakes
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Idle question?
I'm starting to nitpick now... I've noticed that the car doesn't idle as smoothly as some of the other cars I've driven. The tach doesn't bounce at all, but it almost feels like it *slightly* misses occassionally... is "just the way it is" or something I should look into?
12-02-2004, 03:05 AM
#3
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Dennis,
There are several causes for rough idle:
1. Carbon build up in the Idle Stabilizer Valve or the valve is sticking
2. Winter gas
3. Worn Spark plugs
4. Carbon on valves
5. Dirty injectors
6. Vacuum leaks
Also, our cars are made to run "lean" during deceleration and idle
to meet EPA regulations. The result is more DME internal closed loop
internal feedback control is required to compensate for the lean air fuel mixture.
This control circuit will occasionally "search" for optimum conditions
resulting in the idle bounce or RPM settling.
I suggest checking your ISV for carbon blockage -it's located on the top
of your varioram intake manifold. It can be cleaned with carburator cleaner.
It can also be adjusted for increased idle speed. ( There's a procedure I posted
somewhere in the Rennlist archives.)
Hope this helps,
There are several causes for rough idle:
1. Carbon build up in the Idle Stabilizer Valve or the valve is sticking
2. Winter gas
3. Worn Spark plugs
4. Carbon on valves
5. Dirty injectors
6. Vacuum leaks
Also, our cars are made to run "lean" during deceleration and idle
to meet EPA regulations. The result is more DME internal closed loop
internal feedback control is required to compensate for the lean air fuel mixture.
This control circuit will occasionally "search" for optimum conditions
resulting in the idle bounce or RPM settling.
I suggest checking your ISV for carbon blockage -it's located on the top
of your varioram intake manifold. It can be cleaned with carburator cleaner.
It can also be adjusted for increased idle speed. ( There's a procedure I posted
somewhere in the Rennlist archives.)
Hope this helps,
12-02-2004, 03:09 AM
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12-02-2004, 11:35 AM
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Join Date: May 2004
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Welcome to the club - have had the same problem since i bought the car. I've cleaned and adjusted my ISV, used Techron a couple times, had 30k service done (including changing plugs & dist cap), had plug wires checked (all fine) and even had the fuel injectors removed, tested and cleaned - still no improvement. If you're a PCA member, check out the tech archives - Joel Reiser has some additional suggestions which I haven't had the opportunity to try yet.
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12-02-2004, 11:55 AM
#8
"I've noticed that the car doesn't idle as smoothly as some of the other cars I've driven"
The ISV generally won't contribute to this problem.
Problematic ISVs cause:
1. erratic idles (not at same values during the day)
2. idle undershoot (idle drops below normal value on de-accel)
3. a low/high idle
A rough idle is generally caused by;
1. lean mixture (fuel pressure or MAF sensor)
2. bad spark plugs (could be a bad lower/upper plug in one cylinder)
3. bad spark plug wire
4. bad O2 sensor causing lean mixture
5. intake air leak (intake manifold gaskets)
6. bad performance chip
7. bad caps or rotors
8. weak ignition coils
Because of the dual ignition systems on the 964/993, these cars can be a little
difficult to troubleshoot these types of problems.
The ISV generally won't contribute to this problem.
Problematic ISVs cause:
1. erratic idles (not at same values during the day)
2. idle undershoot (idle drops below normal value on de-accel)
3. a low/high idle
A rough idle is generally caused by;
1. lean mixture (fuel pressure or MAF sensor)
2. bad spark plugs (could be a bad lower/upper plug in one cylinder)
3. bad spark plug wire
4. bad O2 sensor causing lean mixture
5. intake air leak (intake manifold gaskets)
6. bad performance chip
7. bad caps or rotors
8. weak ignition coils
Because of the dual ignition systems on the 964/993, these cars can be a little
difficult to troubleshoot these types of problems.
Last edited by Lorenfb; 12-02-2004 at 12:20 PM.
