1993 Cobra/125,000 miles -- stock except: shorty headers, advanced
timing, 73mm C&L mass-air meter and an A9L processor.
This combo ran solid for a number of years and the symptoms suddenly
-- no mods or changes were made -- just appeared.
The symptoms have gone on now for about 1 1/2 years.
The frequency of the symptoms has slowly increased from maybe once a
week to almost every day. But despite the symptoms, the car performs
well without any popping, missing, stalling, gassy smells, or smoking.
Reved-up idle. Sometimes. Some days, the car will run fine all day
long, or for a couple days. Other days, the reved-up idle will
continue to happen.
Idle speed varies, but generally sticks -- doesn't roll -- somewhere
between 1600-2200 rpms. Never goes above 2200.
Generally, I get the reved-up idle a few minutes -- 3-4 minutes --
after a cold start AND after I dip into the throttle a little bit.
But frequently I get the reved-up idle when/after the motor is fully
Miles and miles of driving -- 20-30 -- even at highway speeds, often,
won't alter the reved-up idle.
Running the car hard, even really hard, doesn't change the idle (if
anything, it often makes it go higher up in the 1600-2200 range).
Normally, running the car hard will trigger the reved-up idle.
Shutting the car off and restarting _always_
fixes the idle, at least
for a while.
No codes have _ever_
popped up in the computer.
Sometimes the idle will just fix itself while driving.
And a few times _while reved up_
I've had it just fall to the normal
idle speed and stay there. And a few times, after falling to a normal
idle, I've had it return to the reved-up idle -- like someone is
controlling it by remote.
A scan tool was run once while the idle was reved up and, for some
unknown reason, the reved-up idle didn't return for nearly 4
months. Also, a few minutes _after_
the [scan] tool was
the idle dropped to normal and then a few minutes later
it reved back up. Coincidence? My mechanic, and he's extremely good,
was at a loss, but thought the processor might have some issues.
(Note: My mechanic drive my car home that night and the car ran
PERFECT for him. It's about a 40-mile loop for him to drive to and
A few weeks ago, I noticed on two occasions, a missing while driving/
cruising at highway speeds. The missing has since gone away.
Also, after a cold start leaving work one day, a few weeks ago, the
idle went below the normal idle speed and the car acted like it was
going to stall. After a few minutes of driving the problem went away
and hasn't returned since.
Treatments used so far, in this sequence:
1) Fuel filter
2) New TPS
3) New Air-Idle Control valve
4) New Mass-Air sensor (the actual sensor unit in the mass-air meter)
5) New A9L Processor
Each treatment was used independently, but nothing has helped/worked.
Besides a gun, does anyone know of a cure?