Murray

I while back I bought a set of Autothority chips and installed in my stock 89S4. I have read the threads about S4's not benefitting from these but they were inexpensive enough to warrant the experiment.

They did make it livelier in the midrange and changed the exhaust note too. I liked the (perceived) performance change. However, they also raised the idle to around 1000rpm. I did not like that so I removed them.

Later I installed an X-pipe and replaced my O2 sensor. For the heck of it, this weekend I decided to try the chips again to see if the X-Pipe and O2 sensor made a difference. Well again it felt much livelier in the 3K rpm range and up and the exhaust note was even deeper and more pulsing. (I like the sound)

Now the strange part is that the idle is now lower than normal at around 600rpm when fully warmed up. If it idles for a long time it will occasionally stumble at this low rpm and hunt for idle a bit before smoothing out. If I rev it up a few times (blip the throttle to about 3k) it will settle into a smooth idle at 600-700rpm.

Would the addition of the X-Pipe and new O2 sensor account for the change in dle behaviour in thw AA chips? Is there a way to adjust the idle up a bit on the S4 (I don't have access to a shark tuner)?

Thanks for any feedback.

Murray

AO

The chips should not have affected the idle IIRC. I believe the idle map and such are the same. So I think it was probably coincidence.

However, the addition of a new O2 sensor may account for this. If you have not done so, you might try a battery resent (although unplugging the LH should have accomplished the same thing). The LH goes through an adaptation cycle. It can take a while for the LH to "re-learn" things.

The X-pipe should not have had much if any effect on things either except if your car had the auxilary air pump and it was disconnected. There is a vacuum line to the control unit for it that needs to be capped otherwise you will have a vacuum leak - but that would cause the idle to increase, not decrease..

Murray

I did remove the belt for the smog pump and the hard line from the pump to the old cats is disconnected. Everything else was just left in place. Do I still need to cap that vacuum line? If so where?

Thanks,

M

AO

#30 in this pic.

davek9

You may want to also check the throttle position switch to see if the contacts are closing in the idle position.
I've seen a lot of miss adjusted or sticking throttle cables too.
The switch has two sets of contacts, one set is closed at idle, opens when off idle to enable cruise map, then at about three quarters throttle the second set closes to enable WOT map.

Murray

Here's an update on this. I have done a battery disconnect, checked the throttle position switch and made sure there are no vacuum leaks at the air pump. I also reinstalled the stock chips. With the stock chips back in, the idle is still low; approx. 600 or so. It is however, much more stable than it was with the AA chips in there.

So are there any things that would just cause a low idle. Its not hunting or stalling, just lower than normal.

Thanks

John Speake

ISV stuck, or failty LH. The idle speed should always be stabilised to 675rpm when engine is at normal temp. 100-200rpm higher when engine is started from cold, dropping to 675 when at 80degC.

Murray

Thanks John. I'll try one of the procedures for "unsticking" the ISV that's posted on Rennlist. Your website also indicates that the diagnostic tools like the Hammer can reset the idle speed on a 928. How does that work? and how available are these diagnostic tools?

Thanks

John Speake

If everything is on good order, then you shouldn't need to use a diagnostic tool to adapt the ISV loop.

Without a diag tool, resetting the stored adaptation parameters in the LH ECU by disconnecting the battery ground strap for 10 senconds will clear out any bogus values.

Does the idle speeed hunt up and down at all ?

Murray

When I put AA chips in this last time it would occasionally start hunting for idle if it got really low. With the stock chips in there it idles smoothly, but at about 600 when warm. Reacts fine when in gear or with AC on. Will drop a bit lower than 600 when I come to a quick stop and will quickly come back to 600. It has generally always idled at 675 until now.

Speedtoys

Dump the AA junk, find someone that knows how to use a shark tuner after all of the requisite intake and exhaust upgrades.

Murray

I have gone back to the stock chips. I am looking to solve a low idle issue with the stock chips. I would love to find someone who could shark tune my car or provide a set of chips from a well tuned 89 with X-Pipe and EIS (my next purchase!)

Speedtoys

Sharktuning without good intake and exhaust mods..is an interesting waste of time.

X pipe with large xhaust behind it, and EIS are bout the right places to go.

You may ask Jim Corenman how he feels about sharing my 88 S4 tune with you that he helped me finalize in April.

Murray

Thanks Jeff. I will follow up with Jim on that. How much difference did the sharktune make for you?

Speedtoys

Right in the 20Hp area, or thereabouts.