Driving along, put in clutch and brake to stop at a light, idle drops down to 400 RPM, shoots up to 1100 RPM, oscillates for a bit and settles at around 725 - 750. Once in a while it will stall.

14K miles....going in for 30K service next week.

A search of the archives leads me to think it could be a bad ISV...thoughts?

 

P.S. - it wasn't doing this until I just installed a new Optima Battery....or at least I hadn't noticed it.

 

DC,

Yes, this could be a bad or dirty ISV. When you push in the clutch and come off the throttle, the only way the engine gets air is through the ISV. If it responds slowly due to dirt or gunk preventing it from opening quickly, you could get an RPM dip like you mentioned. The DIY for cleaning the ISV is simple enough, so give it a try.

It doesn’t make sense to me that the battery is at fault, but there is your experience and the other recent post mentioning the same thing. I suppose weirder things have happened…

Tom
’95 993

 

Isn't there a period of adaptation when power is disconnected from the ECU and re-connected? Could this have some effect?

 

DC, as you recall Steve W's advice before a service: bottle of Techron, then Italian tune-up on the last tank of gas before the tune-up. In the last 30K miles, I have had a half dozen occasions of stuck at 2500RPM when I put the clutch in. Always solved with the Techron treatment. I plan to have the ISV cleaned at the 90K next month or so.

 

I am picking that up tomorrow and will be stretching her legs over the next week as well as on the 80 mile trip to the dealer.

This might be the down side of buying a low mileage car.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by DC from Cape Cod:
<strong>Isn't there a period of adaptation when power is disconnected from the ECU and re-connected? Could this have some effect?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Yes - two or three drive cycles (cold start, drive for a while, then shut down). Sounds like you've done at least this many.

Tom
'95 993

 

I've done 2 trips - each 2 ways. Two were 10 minutes each and two were 15 minutes each.

I am due for a long drive this weekend and another next Thursday.

 

Silly question - could this be a vacuum leak?

 

Follow up - Apparently installing a new battery causes the ECU to lose its memory. Thus, when power is re-connected, the ECU starts of with curves from the factory and it takes a little while for the ECU to re-adjust to the car.

Car is now fine - problems where most obvious during the first few minutes after re-installing the battery. After a 170 mile round trip to the dealer for some service, the car is now like new.