Hunting surging idle

Scott R · Scott R's Garage

My luck continues, I have a surging hunting idle condition that goes from 900 to 1300 like someone is blipping the pedal. It's a fast oscillation that doesn't show up on any of the normal tests.

Control pressure 3.6 bar steady as rock
Warmup is perfect idle is up and warms up in a normal amount of time (no hunting)
Duty cycle is correct during warmup and when warm
mixture is 1.0 ~ 1.2% CO when warm

Now the weird part, this condition starts as soon as the high idle warmup stops. You can't change it with the mixture, right or lean it does it. You can't change it by disabling the O2 sensor. But.... I can get it to stop if I advance the timing outside of the normal range.

Do you think my distributor is somehow dead.. again?

Joe Bob · Joe Bob's Garage

02 sensor may be the culprit. I had those symptoms....

DRACO A5OG · DRACO A5OG's Garage

Tap on the ICV when she hunts, if she settles down then the ICV is the culprit.

Check your base idle as well.

Jim

Scott R · Scott R's Garage

Joe Bob, I just replaced the o2 last weekend, but I'll get a new voltage output from it. It does this if the o2 is disconnected as well, when it's disconnected the duty cycle goes to default and it still hunts.

Drago, it's an SC, LK-jet system, no icv.

r_towle · 07-17-2011, 08:00 PM

Here is what I figured out.
At Idle, the idle switch puts the computer into idle mode, thus its running off a pre-determined map built into the computer.
the O2 sensor is not used, nor listened to. (I also unplugged mine)
the sensors that do come into play are the speed sensor, tach sensor.
The ones on the flywheel I would suspect first....just for being clean and sending the proper voltage.
Check to see if the wiring to your tach is all clean, grounds clean etc.
Mine is a 3.2, so YMMV.
Reading your signature it states you have webers.....is this a different car?

Rich

Scott R · Scott R's Garage

It's no longer webers, it's a brand new CIS system installed after a fire I have. Airbox, WUR, FD, AAR, AAV, pipes hoses injectors and metering plate all NOS. The non-stock items are the engine itself and the MSD ignition.

Scott R · Scott R's Garage

Fixed tonight. Vacuum retard pod on the distributor had a bad leak. The retard would suck in then back off quickly as it leaked out. Replaced with my spare distributor and everything is fine now.