mac109

I also have the occasional bounce and stall.....I have the 514 part number and assume it is the original ISV.

sml

I tested out the theory with the 531 vs 514 ISV part number difference.

Using my list below, I purchased a 531 ISV from type911.

Autopartsworld was cheaper but they could not confirm if it was the 531 or 514.

Installed the new 531 ISV this evening.

I did not disconnect the battery to reset the DME adaptation settings.

There was no difference in the small idle bounce or generally driving gear changes etc.

Even though there is zero difference, it's nice to change-out a 20 yr old part.

---------------------------

pricing as at 12 feb 11 in USD ...

vertex auto: $249 but lists the 514 part
pelican: $320 for the 531 bosch part
pelican: $538 for the genuine porsche
autopartsworld: $146 bosch
type911.co.uk: $192 bosch
design911.co.uk: not available
porscheshop.co.uk: $396 bosch (called auxillary air valve)
RMeuropean: $302 bosch - shows picture of 531
autoatlanta: $307 bosch
ebs racing: request quote - too hard
dc automotive: $215
patrick motorsports: $324
rockauto.com: $263 bosch 531 part
autobarn.net: $237 bosch 531 part

dlpalumbo

I purchased the 531 part from Rock Auto. I was hoping that the 531 part would have a different adjustment or calibration than the 514 part. My theory was that the 514 part was adjusted to a lower default airflow that caused the idle to undershoot before the ECU could recover.



This is actually the new piece. The valve is against the adjustable stop so it can't get any wider. The opening on the new piece is identical to the old piece and I can tell you now that the new part, 531, behaves identical to the old part, 514. The 514 part costing over $100 less though.

So I began to wonder if I couldn't adjust the old part to have a wider gap, thus a higher default idle speed, and thus a reduced idle bounce. The adjust screw is encased in epoxy. After much drilling, scraping and patience, I managed to coax the adjustment piece out with an easy out. If there ever was a hex head, it was gone now, so I glued a hex bolt into the hole in the adjustment's head.




I could now adjust away.




After many attempts at much wider and much narrower gaps I can report that THIS DAMN ADJUSTMENT SEEMS TO DO NOTHING .

I guess its only use may be to reduce emissions when you lift the throttle.

So the good news is that the cheaper 514 part seems able to replace the outrageuously priced 531 part. The bad news is I still dont know for sure how to fix the idle bounce.

Pursuing the "it needs more default idle airflow" theory, leads one to the throttle plate. I have in the past removed all the intake up to the throttle body and sprayed cleaner blindly into the throttle hoping to clean it up. This didn't work, either because its not the problem or I didn't succeed in cleaning anything that well.

So, one thing to try is to take the throttle body off and give it a good cleaning.

There is a way to adjust the throttle plate and I found the adjustment, but I needed a mirror to see it way under the linkage. I couldn't really get to it to fiddle with it. I think if I take the intake off again, I might be able to get to the screw, however, I'm not sure I could run the car to do the adjustment as the AFM and maybe the ISV would be disconnected.

If anyone has a suggestion on how to do this adjustment, I'd like to hear it.

Other than that, I might try cleaning the throttle plate again, this time with more intent.

The next thing to consider would be fuel pressure. Like the deficient airflow theory, if the fuel pressure was low, the default idle fuel metering might be insufficient and the ECU would have to recover by adjusting the ISV.

Ideally one would like the idle to be on the high side so the ECU could gradually adjust the idle down. Instead I have this undershoot condition which causes an overshoot, thus the bounce, before eventually hitting target.

Makmov

FWIW files.

When I got my car the idle was so bad it often stalled. Undestand the car was sitting for 5 years with even started once until recently before I purchased it.

Just driving it improved the idle but it was still very bouncy.

It came with a K&N filter that didn't fit correctly and I replaced it with a proper Mahle filter.

I replaced the DME relay and it helped but it was still bouncy.

I repalced the O2 which also improved drivablity.

I cleaned the ISV and gained another small improvement.

A couple days ago I replaced the fuel cap and replace the Fram fuel filter that I came on the car with also a proper Mahle filter and it's run flawlessly for three days now.

Not sure if it was just the fuel filter or maybe the seal on the fuel cap was starting to leak. I know it kind of sounds like a real long shot but the idle is up just a little all the time to about 850 where it should be and the bounce has completely dissapeared.

I don't believe it myself.

I was just about to order a new ISV, too. However, I think not, at least for the moment.

sml

I think I have read every thread on 964 idle problems.

There were 1 or 2 people that said their car never idles correctly until a Bosch Hammer system adaptation.

The majority said that the battery disconnection technqiue was the same as the Bosch Hammer system adaptation.

To try to resolve the idle dipping (I may or may not have a LWF), I have tried:
- new ISV
- Steve Wong chip
- new coils
- new fuel filler neck & cap
- checked for vacuum leaks
- new air filter
- cleaned AFM
- fuel injector cleaner fuel additive
- new oxygen sensor

I have tried the battery disconnection technique 20 or 30 times ... when cold, when hot, idling for 10mins, blasting for 10 mins.

The car continued to have an idle dip .. when the revs dropped.

Today I drove to the mechanic with the usual minor slight idle dipping.
Bosch Hammer system adaptation.
I drove home without idle dipping.
I didn't touch AC compressor, fans, lights.

My conclusion is that the DME reset with the battery disconnection technique is very different to the Bosch Hammer system adaptation.

dlpalumbo

Thanks SML, I'll give it a try.

Anyone know if the Durametrics software does the adaptation?