"inherent SC CIS problem"
 

I appear to be having a problem similar to NOSTATIC. While driving down the road the car drives fine.... but come to a stop and the idle searches up and down till it dies... If I "manually" stablize the idle it stays generally, well....idle, but will still search a little. I phoned the P.O. and he said that twice a year he would take the car in and have them "tweak" the FI and that "inherent SC CIS problem" would go away. he said he would have it done in the spring and the fall and the car was good. My question is... what are they "tweaking" and can I do this myself? Brian

Hi Brian.

Shouldn't have to tweek it every 6 months. I've had my car for seven years and have only had the CIS looked at a couple of times. Try doing a search for Auxiliary Air Valve (AAV ), or it may mean you have a vacume leak and it's weakening your mixture. To find a vacume leak spray some carb cleaner on the various hoses and if the idle goes up it means it's sucked some of the ether into the engine through the leak.

Good luck, Bill '79SC Euro.

Preface: I am not an expert. (nor do I play one on television)

If you have the adjustable type WUR, the PO might have been having the pressure adjusted. I understand that the idle problem might change with ambient temp. That might explain the 6 month interval.

I also understand that while adjusting the pressure on the WUR changes not only the warm up period but post warm up as well.

Any experts out there care to comment.

My 79 started doing the same thing after the weather cooled off. I've been tweaking the decel valve screw a little at a time and have improved the prob, but not fixed it completely. Some people have the decel valve disconnected and reported that it fixed CIS issues they were having. I haven't tried that yet.
Mark

The engine will hunt at idle if the fuel mixtue (02 sensor) is not correct. I have an 80 SC with K jetronic fuel injection with Lamda. It would hunt at idle after inital warm-up. I adjusted the mixture using a dwell meter attached to the 02 test jack in the engine compartment. The meter needle would cycle back and forth in in sync with the idle. I adjusted the mixture until the meter needle stayed fairly constant in the middle of the guage. I have the Bosch fuel injection management book. The book describes the different fuel injection systems and how to troubleshoot them. The book described how to use the dwell meter if you don't have an 02 meter. I don't know if the 79SC came with the Lamda and 02 sensor.

'79 has an airpump...no O2 sensor. I beleive all years ROW SC have an air pump too.

My problem has only happened once or twice at sea level, but was persistent yesterday at 7000'. Don't think it was totally temp related as I've driven at night with about the same ambient temps as yesterday in the mountains...BUT the humidity was much lower yesterday in the mountains.

I drive my 78SC year round as a daily driver in temperatures as low as -25F. Here is what keeps a CIS system running.
1. Take out the AAV (Refer to previous posts).
2. The deceleration valve should be connected and set properly. (Should take a few seconds to return to idle when warm.)
3. Set the fuel rich if you don't have O2 sensor. (3 to 5%).
4. Set the idle to 1,000 rpm when warm.
5. Use fuel injector cleaner at least once a year.
6. I think the WUR is blamed for many things it doesn't cause, but it's a nice expense part that’s easy to replace. If you’re paranoid do the pressure tests. (JC Whitney sells the pressure tester for <$100.)

According to my sources, adjusting the WUR does not affect fuel pressure at oprating temperature. It only affects fuel pressures during warmup.

What's this about removing the AAR? I find this curious. Without an AAR, the engine would run like poop while cold. Right?

Before you go nuts with the hardware, make sure you have replaced your gas filter, run Techron through the system on a hard run, and used a bit of Heet or otherwise to drive all water from your tank.

Typically, as the weather changes, you start to include more condensation-caused water in your gas mixture. Combine this with the Ethanol oxygenated gas and you may be due for curious results.

So really what I guess I'm saying is do all the basics prior to playing with other peripheral parts. That means dumping the oil after the Techron run, maybe replacing the 'plugs, and getting all of the crap out of your gas tank. Probably wouldn't hurt to get a fresh air filter if you have not done so in the last two years.

Once you've done this and had your CO checked/adjusted (engine well warmed up) I think you would have license to check hoses, etc. to be sure there are no leaks and everything is working well.

John

I believe the Warm-Up-Regulator functions throughout the operating range, but predominantly at "warm-up" and under "load" or acceleration.

Jerry M
'78 SC

There is one thing to know about WUR's, they need the little helper heating element or they will not lean the mixture even after the engine is warmed up. Following engine work in which the CIS is removed, it is possible that the electrical connector to the heating element is either damaged or not making contact upon reinstallation. If this is the case, the car will run pretty good when cold, pretty good after heat soaking 10 minutes with the engine off, but will hunt in all other cases. This problem is easily confirmed with an Ohm meter at the 24 pin connector.

Well, I don't have the answers and I'm not the expert, but I believe both JW and Tyson told me that when you adjust a WUR, you change the warm-up fuel pressure curve, but the top of the curve (operating temperature) stays the same. I mean, once the diaphragm quits throttling fuel (and thereby changing fuel pressure), then the WUR is not much more than a simple connection between the incoming fuel and outgoing....that, the exit fuel pressure is the same as the input fuel pressure. So, no matter how you adjust it, at full warmup, incoming fuel pressure=outgoing fuel pressure, or at least the effect on fuel pressure is 'fixed' outside the adjusting geometry.

At any rate, I really don't know and I'm not trying to be argumentative. Just reporting that a couple of trusted guys who have modified their share of WURs, say the adjustment does not affect fuel pressure except during warmup.

I said take out the AAV, not the AAR which needs to be there.

The preceding posts prove my point about WUR legend and confusion.

I think you may have too lean fuel/air mixture. I had the same problem with my 78 SC Targa, and after a few minor adjustments on the air sensor plate, and the fuel mixture screw, the problem went away.

Steve

"A Porsche does more then just go fast in a straight line"