Rod Underwood

This is what I did, grounded the body of the ISV to the cross brace connection and it apparently did not "yet" have any effect. I thought that there was a necessity from what John had said that the ISV body be grounded to the engine or somewhere.

Sorry, but I thought the grounding was relevant to the general discussion, I apologize for potentially hijacking the thread.

Rod

Rod Underwood

"Rod, D.R. has, or will have very soon, a new set of chips for your kit. Among other things the new set should lower the idle by about 150 rpm. Also, I've been working with John, off line to understand what 'the code behind the LH curtain' is doing so as to be able to better-tune the ECUs for the TS kit."

Dave, thanks. It's really painful to be dumb. I apologize for my vertical learning curve.

Rod

worf928

aggravation doesn't have the TS kit. So, his idle/ISV issues are not related to this.

The 928 SP TS kit uses two throttle bodies that are quite a bit smaller than the stock units. But, the idle behavior and the operational parameters of the ISV is almost independent of how much air is going through the throttle bodies and ISV bypass. Yes, I know that sounds weird - but its true. I've done several experiments with the TS kit in various configurations.

I have a number of theories as to what might be going on. But, we'll end up with more confusion than logic if we try to work through them in this thread. Let's go off line on the TS, ISV, and Shark Tuner interaction until we can gather some more data.

John Speake

The ISV doesn't need a ground to the engine bloack, I didn't mean to give that impression :-) It gets all the electrical connections it needs through the two pin Bosch connector.

Rod, if you had one ISV in the air path but no power, then the loop is broken. Also, the second ISV with an electrical connection but airpath not connected is similarly ineffective.

The loop is - ECU detects idle speed is too high or too low, send a correction signal to the ISV, ISV responds, LH checks idle speed agian, corrects again as necessary, ad infinitum, many times a second...

worf928

The ISV is not grounded through the body of the unit. The wiring diagrams are pretty clear on this. And they have notations for electrical items that are body-grounded - for instance the head light lifter motor - that do not appear for the ISV.

worf928

Check your continuity as I outline in the previous post; I think you have a short to ground.

If I have some free time this evening I will do an independent check with one or more ISV setups that I do know work and will post the results.

Alan

I also note that the ISV appears to have a 3rd terminal for an additional unused input... anyone know about this one - it appears to have a secondary coil that may also need to be pulse grounded...? presumably this part was used on other vehicles - it would tend to impy two seperate control mechanisms though that would be rather odd in terms of a closed loop system. Maybe it was just an alternate configuration for a variable voltage control mechanism or an alternate coil spec? Anyone?

Alan

aggravation

I'm trying it now, I located a connector labeled W, the bottom right corner but don't know how to tell which wire is #13. The WSM's don't seem to identify it for me either...
I did determine there is no short to ground from pin 33 on the LH connector, harness side.

worf928

Look very closely at the connector. You will see tiny numbers molded in the plug. The inboard set of 5 terminals is the "1" the out board set is the "2". The individual terminal are 1 through 5. So, W13 is the middle terminal on the inboard bank on the W plug. On your 88 W13 should have two red/yellow wires on it.

worf928

The wiring diagrams from 87 to 94 show only two connections to the ISV. I've not seen an S4+ ISV with more than two pins. However, I have not seen a GTS ISV. But, the part numbers are the same for '87 and '94.

The S3 ISV do have three pins. The S3 ISV is mechanically different from the S4.

Are you sure your not looking at the idle/WOT?

worf928

Check that you have continuity from pin 33 to one terminal of the ISV connector.

aggravation

Thanks! I have now done all the checks. I have continuity from 33 to one of the pins, continuity from the other pin to W13 and no continuity, instead infinite resistance, to ground.
Looks like harness problems are out.
I'm going to proceed with SharkTuning the map in the idle range like John suggested.
After checking the harness for shorts I plugged the ISV back in to be ready to do the SharkTuning and took a little ride to see how it behaved, with the engine warm the idle is smooth at 1000rpm's. If it is true to it's previous behavior it would start idling at 1200 rpm's once the car warmed up a touch more.

We'll see what the SharkTuner does for it. I don't want to be tuning to hide a symptom but it is already running great with the exception of the idle being high so it's not like I'm changing the WOT or even medium load part of the map.
The only wild cards I can think of at this point is the EZK has never been replaced...don't know that it could give me the high idle though...
And the replacement MAF is used so maybe it is the source...

I'll do some logging to see how the data looks at all stages of rpm's and load if the idle goes to normal after the tuning and if they look good then hopefully that will be the end of it!

I'm still open to any suggestions in the meantime, I like learning how this beast works!

John Speake

EZK does not affect idle . Do some datalogging with the ST so you can evaluate what is going on.

Check out O2 sensor adjust and idle stabiliser on the System monitor screen.

Alan

No not the TPS - I do understand its not wired to on S4 models - but on the diagrams the ISV looks like the extra pin on the unit exits - see the 87 diagrams for the most obvious indication (pin numbers) - later diagrams show the internals but no Pin ID. On 85/86 models all 3 pins are wired & both grounding IPs are driven from the LH.

You'd think it might be the diagram is just a vestigial hold over - but it appears to be a newly drawn diagram for '87 with more detail...

Alan

aggravation

It was idle stabiliser bouncing around 52% and the O2 was pegged on 20 too much so I just finished installing a new O2 sensor just to be sure. A quick drive didn't seem to change anything but the data logging will have to wait until morning, ran out of time