1980 Bouncing idle, dying, not a happy car..

[catron1]

Hello All,

So....Long story short, I got my car back. "1980 911 SC"

I had it painted in NJ, and had some mechanical work done in NJ as well.

As for the mechanic, I looked up shops on the NJ PCA site, and found the shop, so..idkwtf

The valves needed to be adjusted, oil change, air leak, etc. From the receipts listed below you will find that the WUR was weeping a little fuel, that was returned to Parts Heaven, and a "Rebuilt - New" one was sent out and installed to correct the problem. .anyways, picked up the car and it ran great. I was about an hour into the drive when the car felt like it was loosing power and slightly backfiring during shifts. I got the car back to DC experiencing poor, and I mean poor fuel economy.

Worked on the car over the weekend installing various stuff the paint shop threw away to the tune of $200 in various bolts and trunk carpet set, and noticed that when I started the car to drive it barley started, hesitated, backfired, and the idle would bounce from 1k to 2k then die.

I've done some research and read several things to attempt, namely looking at the Oxygen Sensor wires to make sure they are connected, the pop-off valve and make sure its not loose and J-B Wield it back in place if so, Someone said a relay under the seat?, and to correct the mixtures.... I am puzzled by the mixture part because the mechanic I took the car to had done the proper adjustments.

I have included a couple of pictures of what was done to the car before I picked it up, I have literally put only 140 miles on the car driving it back here from NJ....

Any help would be very, very appreciated, and the Porsche gods will smile upon you..AKA Thanks......

[bordin34]

Two things come to my head. Ignition timing being off or the valve lash getting tighter as you drove forcing a valve to stay open a bit.

[Charlie Stylianos]

Do you have the CIS fuel pressure gauges? More likely something amiss with the CIS or a vacuum leak.

[Cliff Claven]

x2, CIS issues. hard to diagnose without methodically running the tests. check your pressures off the control pressure regulator (because it's "rebuilt"), and then run tests on the fuel distributor. only way to adjust fuel distributor properly is by measuring the exhaust gasses. but you might want to do a leak down as well, just to make sure.

[catron1]

I don't have the equipment to check gasses, or pressures..

I will look for a vaccum leak though, and everything else I can..

[Charlie Stylianos]

Is your o2 sensor connected? Lambda "brain" getting power?

Check to see if pop-off valve is installed correctly and/or a cracked airbox.

Before trying the following, you have to be sure your fuel pressures are within spec and no vacuum leaks.

only way to adjust fuel distributor properly is by measuring the exhaust gasses.

This can be set by ear and its very accurate for best performance. If tuning CIS w/ lambda, disconnect the O2 sensor first. Using this method your idle CO% will fall between 2-4%.

The trick to find your engines happy CO is to get the engine at least running and with the airbox cover and filter off, SLIGHTLY lift the air sensor plate via the exposed elbow with a finger, knuckle or whatever. All is needed is very slight pressure to notice any change in RPM. If the engine RPM increases it wants to be richened. This is also true if you were to pull down on the sensor plate. If RPM's increase, then it wants to be leaned out. Make very small adjustments with the 3mm allen as necessary. The trick is to get the engine at a max RPM so when you either push or pull on the sensor plate, the RPM's will drop (from either being too lean or rich).

[Cliff Claven]

^^^good to know! was not familiar with that method.

[Dr K]

Is this a great site or what!!

Matt de Maria is a master with setting CIS. Not too far from DC (in Gaithersburg). See PM.

[turbo23dog]

1980 911SC has a rudimentary brain controlling the CIS. It's located under the passenger side front seat. It has a 4 prong relay controlling its power. If this relay goes bad, your car will run Like crap. Something to think about...

[catron1]

I did a slight idle adjustment to 1.2-1.5k, It runs like a top, with no more surging. When you let it idle at 1k it starts surging again, I think it needs to be leaned out, its running very rich.

I had seen this on youtube, great video..., I still need to take it to someone who can dial it down better than I can..

Porsche surging idle repair-How to--HD - YouTube

[BlackTalon]

Did you try the relay yet? Did you check for vacuum leaks? You really should do both before you start fuching with fuel mixtures, or you may make things a lot worse.

[catron1]

I did both, the relay was good, and I couldn't see any air leaks. The only thing that I had seen that was suspect was the oil breather hose was loose, but after getting it straight, it didn't make any difference to the surging.

All I have done so far is adjust the idle up slightly so that the surging stopped, problem is that the surging only stops at 1.2k, and it smells rich.

[Intubator]

Here's an old school trick to find a vacuum leak, you may have tried it. Get some carburetor cleaner with the tube attached to to the nozzle and spray it at all of the locations (one at a time) where you might have a suspected leak while the engine is running. The cleaner is combustible and you will located the leak when the engine idle increases and slightly smooths out, indicating the area of the leak where the cleaner is being sucked into the combustion. You obviously want to be conservative with this as it is flammable and I would not do it on a super hot engine on a 100 degree day...

[Noah]

http://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies.html

[Intubator]

Hey Catron1, Did you figure this thing out?

[catron1]

Hey Catron1, Did you figure this thing out?

Funny that you ask!

I have 86911TLCAB helping me out with this hopefully over Black Friday "Wife Permitting"..Which I'm trying to massage the situation...

But...

I am putting together all of the parts that I need for fixing the system, and I am looking for another CIS box as I write this. So I will keep you in the loop for sure.

-Bill

[Charlie Stylianos]

and I am looking for another CIS box as I write this

Is you current CIS air box cracked?

[catron1]

I don't want to do all of the work with doing a partial drop, replacing lines etc. and it be a cracked box and not have one.. So really it's a backup of sorts.

[Charlie Stylianos]

A vacuum leak/cracked air box is pretty easy to diagnose with propane. Maybe just a pop-off valve that has become unglued?

How To Find A Vacuum Leak - EricTheCarGuy - YouTube

[86911TLCAB]

just a quick look shows many lines on the CIS are old and rotting...so figured a good way to start was to pull the CIS and just swap them all out...at least then we know the air system is lock tight...i pulled the oil cap last week with the car running and there was no change in rpms...so figured i would teach bill how to take it apart, and give it a good cleaning, freshen up all the air lines and gaskets...and drink a few beers at the same time...plus gives me a good excuse not to go shopping on black friday...