Re: ISV Questions, 1988 90q (longish)

[DeWitt Harrison <de@aztek-eng.com>]

On Mon, 25 Aug 1997 10:25:07 -0400, Kirby A. Smith wrote:

> [ ... ]
>I have some Idle Stabilization Valve (ISV) questions which follow after
>the background information below.
>
>Last week I was having some routine service done and complained that my 
>idle was running at 1200 rpm (warm, w/o AC) and hunting.  My mechanic du 
>jour hooked up a digital multimeter into the ISV circuit and adjusted
>the %CO screw (in the metering head) until his meter read a sequence of
>current values (he said, I didn't check the hookup) that had a nominal 
>2.5 mA mean.  He suggested I clean the ISV and reset the current as 
>required.  He said, reasonably enough, that the jittering readout 
>indicated a properly functioning oxygen sensor.

Sounds really fishy. 1) To set the %CO, one ought to measure the %CO.
2) ISVs that I have measured on the bench begin to open at approximately
430 mA DC. Although I do not know whether the ISV is operated with
pulsed current - I suspect it might since that seems to be an economical
means of controlling this sort of actuator motor - I have had no trouble
obtaining reasonable readings (400 - 550 mA) on the car with a using a
decent digital meter.

The mechanic would have been correct about duty cycle jitter and the
O2 sensor if he had been talking about the O2 frequency valve.

> [ ... ]

I leave it to a better man than I to offer actually useful CIS troubleshooting
tips.

DeWitt Harrison   de@aztek-eng.com
Boulder, CO
88 5kcstq (with a fire extinguisher within easy reach of the driver)