Got Her Running...Finally (Erratic Idle)
 

Well Folks,
The bottom end rebuild is complete and she's finally on the road and running quite well...except for the fact that an old ghost showed up. I have an erratic idle problem that popped up again. It doesn't do it all the time but when it does, it's pretty annoying.
I can turn off the ignition, start it up again, and it runs ok for a bit, but then starts again with the erratic idle. I can hit the gas to cause it to idle at 1200-1300 rpm and it stops the erratic idle, but then I'm idling too high (which is way less annoying than the alternative). As many times as we've had it running during the rebuild process, it's never done it until yesterday. I figured if it was a vacuum leak, it would do it all the time.
Any ideas?
Thanks,
Mike

Check the TPS Throttle Position Switch
http://www.clarks-garage.com/pdf-manual/fuel-06.pdf

How erratic is it? As in, what is the rpm fluctuation? I have a fluctuation of about 50 rpm but I'm sure it's nothing to worry about and the car runs just fine regardless.

How Erratic Is It...?
 

Thanks for replying one and all,
She normally idles between 1000 and 1200 rpm (mostly stays at 1050 rpm). When it does the erratic idle/rev thing, it runs from 750 to 1200 over and over again.
It was doing it quite a bit today and all the way home until I got it in the garage and then I couldn't get it to do it at all. I turned it off and on again several times, but it ran decent between 1000 and 1100 rpm.
What do you think?
Thanks,
Mike

Perhaps your ICV is on its way out? There are testing and cleaning methods out there but it's such a pain to get to.

At this point, I'm willing to endure a bit more pain to fix the problem. How can I test it to see if it's going bad? Clark's Garage only covers this procedure on later model 944s and I have an 1983. How much of a difference is there?
Thanks,
Mike

p.s. I did find a page to download the Porsche 944 Workshop Manual in pdf form. I found this online and I've been trying to find the page on the ICV, but haven't yet. Anyway, any Porsche 944 owner who does repairs could use this info. It comes in six separate files and it's my way of saying thanks for the help. Here ya go: http://rapidshare.com/users/Z1NM2B password is "pdftown.com"

NA engine have very little differences between the years.

it's most likely a vacuum leak in one of the hoses or a gasket. use a spray can of carb cleaner or starter fluid and spritz it near potential leak spots. the engine rpm will jump when u find the leak location.

Thanks. I did read that somewhere but I haven't yet gotten around to trying that. Check out my previous post to get your Porsche 944 workshop Manual! All the help is much appreciated!

There are lots of solutions, here's a remedy that has worked on mine 944 Foot To The Floor: Erratic Idle Problem Porsche 944 (Square Dash Model)

massive,

I have the ICV/ISV on my '87 & '88 924Ss.

I understand that your erratic idle solution was specific to your car.

Your comments:
(quote) "Fortunately the fix for my 1984 square dash model didn't require checking for vacuum leaks. The problem was actually dirty electrical contacts on the Auxiliary Air Regulator and Water Temperature sensor on the radiator. This occurs due to the constant heating and moisture that the engine bay is subjected to." (unquote)

Dirty contacts on your Auxiliary Air Regulator or the ICV/ISV on later cars, or any connection can cause erratic idle issues. Everyone should should clean all connections and the grounds on engines. (Porsche Tech bulletin)

The Water Temperature Sensor or Thermofan Switch could affect idle but usually it will cause an overheating cooling system problem.

Erratic idle can be caused by the DME Temperature Sensor located next to the water temperature sensor at the top front of the engine. The DME gets the engine temp to monitor the amout of fuel to the injectors. Cold engines need more fuel.

Erratic idle can also be caused by leaks in the FPR (fuel pressure regulator), FPD (fuel pressure damper), leaking injectors, throttle intake body needing a reseal, bad grounds, dirty electrical connector contacts on top of engine (Porsche Tech article) or the vacuum leaks you have mentioned.

Just my opinion.

I have viewed all of your DIYs and am impressed at the degree of completeness. Well done.

John (aka-kind fellow :) )

Yep totally, now I know what to check if my current solution doesn't yield results :)