New to the 944 - help me ID these parts

[jasonmx5]

I'm trying to diagnose a rough idle problem where the car idles really low and then just dies, but if I disconnect a vacuum line between "D" and "C" the idle jumps up and holds steady. Unfortunately, being new to 944s, I'm not sure what "C" and "D" are. Car is an '83 and I just got it running after sitting for over a year, so any advice is greatly appreciated!

[speedracing944]

I think D is a vacuum canister and it looks like C is a check valve which only let flow go one way. My '83 does not have C. You are getting a raised idle when you disconnect these because you are introducing a vacuum leak into the system. You have something else going on.

Is there black soot coming from the tail pipe?

Speedy

[jasonmx5]

Couldn't feel any vacuum at then end of either hose when I disconnected. Disconnected another hose where I could feel vacuum. When I disconnected that hose, engine nearly died until I put my finger over the fitting. No black soot. Ran it up to about 5K rpm and got a good bit of moisture. Recently replaced the speed and reference sensors would too great a gap for the sensors cause the idle problem?

[speedracing944]

I am not sure if the sensors would cause that problem. How did you set the gap? Unless you moved the mounting bracket I would think you would be OK. Did it idle like that before you replaced the sensors?

Speedy

[jasonmx5]

Wouldn't start before I replaced the sensors. I bought the car not running, so this is the first time I've heard it run at all. I had to remove the entire bracket to get the sensors out, so I dropped the bracket back in, installed the sensors, botttomed them, and then backed them off a hair to set the gap. Fired right up the first time after I did that, and actually runs pretty smoothly, except for this idle problem.

Problem seems more prevelant when the car is cold - barely holds an idle for about 10 seconds before conking out. Once warm it will hold an idle, but if you hit the throttle, when it tries to settle back down, the idle drops below 900 rpm, then sometimes recovers, sometimes stalls out.

I suspected a vacuum leak, but haven't found one yet, or a bad regulator or sensor somewhere, but - again, being new to this car - not sure where to start exactly. I suppose I could systematically eliminate things by using proceedures on clarks-garage.com, but I was hoping someone might be able to narrow my search if I could describe the problem and Identify the stuff that I'm not sure about.

[speedracing944]

It might be a vacuum leak. Does it pop and sputter at idle? Is it sluggish to respond when you blip the throttle at idle but respond better when the revs are higher, above 2500 rpm?

Speedy

[VII]

unless I'm mistaken, C is supposed to be between the brake booster and a vacuum line that runs along the firewall to the cannister. I have an '89 but I'm almost positive that C is the check valve for the brake booster. There are a handful of vacuum diagrams floating around and I bet one of the problems you have is mixed up vacuum lines. Do a search to find the diagrams. Best of luck.

[Techno Duck]

A and B are for the fuel vapor purge. The vacuum line connects to the thermovalve on the rear coolant pipe on the head.

D is a vacuum tank, helps control surges in vacuum.

C is a check valve as mentioned. Forget on the n/a exactly but it connects to the brake booster fitting, the fitting also connects the larger vacuum hose to the intake manifold. Usually it's right off the brake booster and runs along the firewall if I remember right, I don't remember what it connects to though. I would double check all routing.

[jasonmx5]

Cool. from what I can tell, the check valve ("C") is defnintely not routed to the brake booster in any way, but I'll double check. From what I can tell, the check valve is currently in line between the throttle and the vacuum tank. There doesn't seem to be any mention of the check valve in any of the vac diagrams I have seen

[exitwound]

On my 86, there is a check valve connected to the brake booster.

[jasonmx5]

Originally Posted by speedracing944

It might be a vacuum leak. Does it pop and sputter at idle? Is it sluggish to respond when you blip the throttle at idle but respond better when the revs are higher, above 2500 rpm?

Speedy

It does sputter at idle and sluggish when you hit the gas, but it is fine above 1000 rpm. Have yet to drive the car as it also needs a slave cyl. that I have yet to replace and I've discovered an oil leak that will need to be addressed.

[Gary2397]

The C is call check valve. It should not be there. Its location is at
the brake booster. On the posted pictures, the purple line goes
to the vacuum canister and its brake booster. I hope this solve
the problem.

[jasonmx5]

These photos help a ton. Where does the one that is coming of the throttle and toward the firewall route to?

[Techno Duck]

The end going under the intake goes to the FPR and FPD (it T's off at the fuel rail). The other end goes to item B for the fuel vapor purge.

[jasonmx5]

Ya. I think I just answered my own question with this:


Now I'm just scared as to where everything else is routing . . .

[nightheart]

My 83 has the vac routing in the owners manual or this should be under the hood.

[zedsn]

If you fix your vacumn lines and still have the idle problem check your idle contol valve as well as the hoses that go to and from your control valve. Sometimes they crack with age and let excess outside air in causing an idle problem. You can check your idle control valve to see if it works correctly on Clarks garage and you can clean it out as well if dirty inside. The valve has 2 wires going to it and is at the rear of your air box down below if i remember correctly.

[jasonmx5]

Thanks. Upon closer inspection, I found several loose hoses. I tightened up some clamps and that seemed to help quite a bit. Still a little rough when cold, but significantly better. Also, my brake booster does not have a provision for the check valve to come off of it.