bd0nalds0n

Last week I started having a problem where the car really didn't want to idle...plugged in my ST2 and discovered the ISV voltage was low to non-existant. Then after the car would run for a few minutes/warm up/get revved to high RPMs it would "snap" on and the ISV voltage and %'s would be normal and the car would idle fine.

I assumed the ISV was gunky and sticking...so I ordered a new one and replaced it today.

No love.

Sooooooooo....

What's next on the list of things to check? The LH is rebuilt from John Speake, and is around 15 months old...

I would guess either wiring/intermittant connection or the LH.

Anyone else want to hazard a guess?

the flyin' scotsman

TPS and TII all good?

bd0nalds0n

I think so. If I disconnect the TPS the idle changes.

The ISV % shows 0.2% on the ST2. There is no change when I unplug the ISV (my ISV is mounted within easy access due to the supercharger), and if I plug in the extra, it doesn't move/cycle at all.

Under normal idling conditions the ISV % was reading in the 60s and 70s, percentage wise.

Bill Ball

The ISV gets power from the LH pin 33 and shares a ground with some of the injectors. John Speake should be able to tell you whether that means something is wrong with the LH. Did you wiggle the LH plug? Might be a loose contact.

GregBBRD

I've had a few idle stabilizers short out and short out the brain, killing the power supply, which requires both a new idle stablilizer and a brain to repair. Doesn't make much sense why this would recover after running the car, however.

Could the battery be so marginal that the alternator needs to add voltage to the system, before things get normal?

John Speake

Does ST2 show that closed throttle switch is being registered as working reliably each time the hrttle is released ? The ISV showing 0% shows it is getting no signal (normally a 100Hz square wave with a variable mark/space ratio) to open/close the valve's air valve.

As the problem is intermittant I would suggest a bad signal or ground connection. As you have access to the ISV connector, it would be good to see if there's a signal there. Use a DVM on a.c. volts. I would expect areading of about 1-2v rms. The symptoms you descibe are not typical LH failure.

I have sometimes seen LH on he test jig that under certain conditions the ISV puls virtually disappears, an igntion off/on resets it.

What is your O2 loop % typically when idle is good ?

the flyin' scotsman

Perhaps this should be a new thread but I pose the question of rebuilding/redesigning the ISV...........this part is antiquated.

bd0nalds0n

The car cranks fine, and I get 13.4+ volts on the ST2 after it starts. When I mention working okay after some period of time, it's not like 30 seconds later, but measured in minutes...although over the last several days it seems to be getting progressively worse/taking longer to "snap" on.

I've also been running the car in "ignore the o2 sensor" mode, so I don't think there's an o2 loop% is relevant under such circumstances?

Is the LH vulnerable to low voltage during cranking? I have had a couple situations where the ST2 loses connection to the LH during cranking and I have to reload the maps. Could low voltage during cranking cause the ISV loop to de-energize and remain that way? It's been colder in SoCal, but not bad...and the car has certainly sat longer before, and cranked slower before, and still started and run fine after firing up...

I confirmed that the TPS works, cycling between IDLE and CRUISE as it should.

Using a digital volt meter on the ISV wire (with black on one terminal and red on the other)--and I profess to being a bit of a novice/idiot as far as using it is concerned--if I set it on 20 DCV, I get ~13.20; if I set it on 750ACV I get ~26 (which appears to be a doubling of the DC reading).

bd0nalds0n

Well, I just went out for a drive and got the car up to operating temp...and it didn't "snap" on this time. Just stayed at 0.2% from start to finish.

I think the next step is probably to send to Louie to have him bench test the LH. If the LH is okay, then what remains must be a wiring or ground problem.

If there's something else I should check in the meantime, I'm happy to and welcome additional suggestions.

the flyin' scotsman

Brian............did you swap the leads on the DVM when measuring AC volts?

John suggested 1-2 rms volts (root mean square or 0.717 of peak) which your DVM should read on AC volt setting.

bd0nalds0n

Here's a picture of the meter I used...



I had it on the 750 ACV setting with the red lead in the center hole and the black lead in the bottom hole...

the flyin' scotsman

You may want to try a different meter that can read lower AC voltages:

http://www.universal-radio.com/catalog/meters/1496.html

bd0nalds0n

Am I imagining things....isn't that the same meter? I guess I can put it on the 200 setting rather than 750...?

the flyin' scotsman

Same meter.........I was looking at it to see how else to use it.........I tried blowing up the pic to ensure lead position.........does the top spot indicate 'ADC'?

If so, move the red lead and remeasure.

My DVM:

bd0nalds0n

Okay, I'll try this afternoon and report the findings.