randyrap

My 83SC had run flawless since I purchased it in January. That was until today. It now has difficulty finding an idle and maintain running after restarting it. Cold starts are not an issue. With the engine warm, the car does not want to idle regardless if it has been sitting for 4 seconds or 40 minutes. The symptoms are the same. The car will start immediately and rev to 1500 rpms and quickly drop only to stall or shoot back up to 1500 and drop again usually stalling by the 2nd or third time. Even if I hold the revs up for a short period and let the throttle off, the engine will keep searching for an idle. Only after driving the car for a minute or two will the problem rectify itself and the idle stabalize at 950. I checked the pop-off valve, air box, lines, hoses and even tried disconnecting the O2 sensor. Judging by the exhaust pipe, the engine is not running too rich.

I know there is an abundance of info on CIS however I can't seem to find anything such as what I am describing.

Any suggestions????????????

Avenger6

A suggestion for hot start problems on CIS cars: Reach behind the fuel distributor and disconnect the plug there. It is the connection to the cut-off switch for the fuel pump. By disconnecting that wire, the pump can run non-stop from when you turn the key on, instead of shutting off again after 3-4 seconds. This will allow you to turn the pump on, wait 15-30 seconds, and then start the car. Letting the pump run for this time will let it completely re-pressurise the system, and should cure the problems you describe.

My car has a bad check valve in the fuel pump, which lets the system pressure bleed back into the tank when the car is shut down. When the engine is hot, it seems to lose pressure faster, plus the cold start injector will not fire when you start a warm engine, so it is hard to get it started and running when hot. I don't want to replace the pump ( the only way to replace the check valve, since it is inside the pump) so I run with that wire disconnected. I just have the habit of turning the key to "on" and waiting for the system pressure to come up. On my car, I can ususally hear the bypass valve in the fuel distributor pop and let a few bubbles escape, and that is my signal that the pressure is up.

The wire can be re-connected any time, since you are just unplugging it, not cutting it. The cut-off switch is there to keep the pump from running on in case of an accident or other reason for the engine to have stopped running with the key is still on. You have to make your own call about the risk of having it disconnected, but at least do this as a test, and you should find the problem goes away. Then you'll know that you have either a bad accumulator or bad check valve, and can repalce them if you want.

epbrown01

Can you describe this plug, especially by feel as I can't see behind the fuel distributor on mine. i feel mostly hard lines back there, with on rubber plug that seems to come from the rubber boot.

I think I've got a similar issue, but not as severe - my car is hard to cold start but does okay warm; I think I lose pressure, but slowly. I'm not replacing the pump until I get my pressure tester, though.

Emanuel

Hladun1

Does your car have an AAV; this could be the culprit. When the engine is cold the airflow through the AAR and richer WUR keep the idle up. The AAV is spring loaded and it could be opening and closing on high vacuum. The AAV serves no useful purpose and can be removed, but you've got to get the plumbing right. What it's supposed to do is provide a little more airflow on startup (it's like holding the throttle open). The problem is that it closes once you have manifold vacuum, engine slows, vacuum goes down, valve opens, engine speeds up and develops vacuum to start the process all over.

GoodWife

I just got our new 75 Targa out of the shop for a similar reason, only it wouldn't start when warm...period. Left me stranded the 2nd time I drove it. Started fine when it was cold. Thought I was flooding it, but turns out it was the check valve as avenger6 mentioned above. Seems the previous owner replaced the fuel pump with a weird brand and the check valve was removed to accomodate it. I now have a new fuel pump and check valve (for a price of course), and the car is now starting and running great cold or warm.

bones

Ig the check valve doesn't check out ....sorry.....don't forget the fuel accumulator.

randyrap

Hi Bones.

It is not the accumulator. If it were, then a vapour lock would cause the engine not to restart only after the engine has been warmed and sitting for a while. In my case, the engine has difficulty warm starting even after being shut off for a few seconds.

Time to get a CIS fuel pressure guage and figure out what the problem really is.

I was hoping someone on this forum would of had the exact same problem and knew the remedy.

What is an AAV and where is it located?

Thanks ................................ Randy

jonw440

On my 83SC it did the same thing. I needed a new fuel distributer.
If I remember correctly There is a "plunger" type thing. I would move it up and down a few tones WITH THE KEY OFF! Then it would start fine.
I sold it before I replaced the fuel dist. I think it was like $500.00. I was told you cant rebuild them.

K Smithson

Randy,

The AAV is the auxillary air valve. Basically a valve with an electrically heated element inside. Closes off as the car warms up. Bumps up the idle when it's cold.

If i recall it's on the right side of the engine, and is fairly hard to access (of course). There is a testing procedure, but I'm at the office and don't have my books!


Kirk

82 911SC

randyrap

Hi Kirk.

The AAV is the round part above the red one in your diagram. The red part is the Auxillary Air Regulator.

I removed the hoses from the regulator and put them together to see what would happen. WOW ....... RMPs went to 3000 and the trottle adjustment screw was useless.

Tomorrow I'll reattach the regulator and play with disconnecting the Auxillary Air Valve and see if that helps my idle problems.

Thanks ............................ Randy

Kirk930

Randy,

Oops! Guess I was wrong........just learned something new!

Kirk

randyrap

I ended up leaning the fuel /air mixture an 1/8th of a turn and setting my idle speed from 900 to 1000. Guess what ............. my idle problems are solved. Weird stuff.

Thanks ..................................... Randy