79 911 SC missing, popping & rough irratic idle.

[ngc414]

I just picked up a 79 911 sc yesterday. The car sat in storage for a little over a year. It runs very rough. The idle is irratic and will miss, pop and stutter. The idle will also surge high in the rpm and dip back down. When you drive it it seems to run pretty good in the upper RPMs. I have done alot of work on cars, but no porsches. So I need advise. I planned to start with the simple stuff (plugs, wires, fresh gas, check timing & oil change) any other suggestions or things to look for?

[Paulporsche]

Welcome. When yoiu can, post a pic of your new project.

First, use the search button here. You will find a wealth of knowledge on CIS and any other aspect of these cars.

Get a Bentley's Manual for your car. Wayne's "101 Projects" book is also very helpful. You can also download from online the Bosch manual for CIS.

You should get a fuel pressure gauge for CIS cars from JC Whitney. This way can you tell if your system is functioning correctly re fuel and control pressures, and the WUR and fuel distributor.

Of the top, the fact that the car sat so long suggests things like bad gas, clogged fuel filter, stuck air sensor and fuel distributor plunger, and possibly clogged WUR. (warmup regulator).

It could also be as simple as your mixture being set too rich, which often causes idle hunting. OTOH someone may have enrichened the mix to make up for some other problem.

Many of us also do specific things to these cars to promote smooth running, incl plugging the vacuum retard to the dizzy, and the top vac line to the decel valve. While some advise that it is not necessary, many of us have had a popoff valve installed in the airbox to help eliminate airbox explosions usually caused by a too lean mix @ startup.

Make sure the dizzy shaft rotates and springs back easily. Oil the wick @ the center of the shaft.

Good luck, utilize the search function and tell/show us your progress.

[ossiblue]

Paulporsche really said it all. I will only add, since you are new to 911's, that these cars need to be driven and sitting for a year can lead to so many minor problems from dried seals, cracked hoses, sticking CIS components, and crap in the fuel lines that the result is what you describe. Have patience, diagnose carefully, read as much as you can about CIS, and ask here often. Once you get things sorted, drive the car regularly and enjoy the dividends of your labor.

[DaddyGlenn]

Post your location. Perhaps one of your neighbors is a Pelican and can lend a hand.

[ngc414]

Originally Posted by DaddyGlenn

Post your location. Perhaps one of your neighbors is a Pelican and can lend a hand.

Thats a very good idea. Im in Wadsworth, OH. Its west of Akron and 45 min south of Cleveland.

[ngc414]

I just checked the plugs and they are gapped at .049, The parts guy said to gap them at .028. Is that correct? I imagine that could be part of the problem. I also checked the pop off valve and it is not leaking, although the burnt hole in the air filter matches exactly where the pop off valve is. Here are a few more pics of the engine. please let me know if anything looks incorrect.

[porsche930dude]

Im sure those taped up plug wires have alot to do with it. I think your right go for the tune up before anything else. Also run a few tanks of gas through it with lots of fuel system cleaner that might just get things loostened up. Do that before you change the oil so it wont get contaminated. Good luck

[ngc414]

What should I gap the spark plugs at? I did a search, but cant find anything for a stock ignition.

[porsche930dude]

.7-.8 mm or .028- .032 in.

[ramonesfreak]

has nothing to do with how your car is running im sure, but whats going on with these bolts sticking out? is that normal?

[ramonesfreak]

its hard to see your green distributor wire? is it ok? just to be safe, i'd replace that coil with an MSD High-Vibration Blaster Coil. mine was original like yours and died a few weeks after i got my car. keep the old as a spare in the trunk

[j_mancini]

Originally Posted by srandallf

has nothing to do with how your car is running im sure, but whats going on with these bolts sticking out? is that normal?

That's where the air pump used to mount...

[fred cook]

Park the car in a dark place, start the engine and look in the engine compartment for "lightning bolts" coming off the coil wire or plug wires. They could be shorting to ground or cross firing. If you need new plug wires (very likely) those made by Magnecor are very high quality and are offered at a reasonable price. See our hosts parts section to order. Good luck on your project!

[Paulporsche]

It may just be the photo, but is that a number 6 wire on a number 5 spot on the dizzy cap? BTW you don't need to buy the factory $tainless $teel braided plug wires.

If you go from the Bosch or Permatune CDI and Bosch coil to an MDS, you can increase your spark plug gap from .028 to .040 or .045.

As others may have mentioned, backfiring through the intake usually means a too lean mixture. The WUR is often @ fault.

Sounds like you did not have a PPI done. Have you checked compression, leakdown, and checked for broken head studs?

[DaddyGlenn]

I, too, think you are on the right track with a good tune up. Since I assume the maintenance history is questionable and you stated the car has been sitting for an extended period, I’d go through a routine to clean it out and get a good baseline on new ignition parts. This is what I would do:

Place an order with our host for; the Bentley manual, the 101 projects book, cap, rotor, plug wires (I went with Magnacore wires), plugs, oil filter, fuel filter (check the part number on your old one to make sure you order the correct part), a set of silicone valve cover gaskets, and the special valve cover washers. You will need the valve cover nuts, too but you can get those cheaper locally.

If the gas in the tank was there when you bought it, drain it. Otherwise burn it down to near empty.

Add a bottle of Techron and only ten (10) gallons of gas

Replace the cap, rotor and plug wires.

Set the timing and idle

Check for vacuum leaks and fix any that you find

You should be running a good bit better at this point but there is more to do to get to a good baseline. Next, drive until you have burned through the gas then add another bottle of Techron and another ten gallons of gas. Drive it again until you have gone through the 10 gallons.

Drain the oil

Change the oil filter and fuel filter

Adjust the valves

Refill with oil.

If you are not running right by this time, we can dig some more.

[ngc414]

Thank you for all the great advise and support. I am ordering all the tune up parts today. I installed the plugs last night. The old ones were coated with black residue. They were also gapped at .045-.048 for some reason. If you look at the fourth pic down on my last post, is that some kind of emmissions recirculation deal? The black plastic Y shaped piece on it has a hairline crack.

[DaddyGlenn]

Originally Posted by ngc414

{snip}....If you look at the fourth pic down on my last post, is that some kind of emmissions recirculation deal? The black plastic Y shaped piece on it has a hairline crack.

That is your heater. Air flows through the big plastic tube to the fan then splits and travels through the hoses to the heat exchanges on the exhaust pipes where it is heated before it is sent into the cabin to cook your toes.

The little electric fan is to keep the heater working when at idle.

[tcar]

Where do you live? Where's the car from?

I see surface rust here and there. Midwest salt on roads or on one of the coasts?

Plug/coil wires look bad - tape.

Symptoms are same as my cd box going out last month.

[ngc414]

The car is from Ohio. The car is very solid, just a couple very minor surface rust spots in hard to get to areas. No more than most newer cars in this area. I see they have some cheaper after market plug wire sets on this site. I was hoping to save some money and buy a set. Any one have any problems with any of the pug wire sets? Looks like this site has everything I will ever need to get this car tip top again.

[ngc414]

Its kind of hard to see but between the rubber hat and the injector manifold there is a thin shaft with a circle shaped handle (see pics below) Is that the adjustment to adjust for lean and rich??