Cogito_Ergo_Zoom

Acquired a 993 in January on a handshake deal and I have to admit, probably unsurprisingly considering the way I bought the car and the lack of due diligence, we're off to a bit of a rough start. Apologies in advance for the lengthy post.

The car had a lot of deferred maintenance, most of which I was forced to address when the car broke down on me on a roadtrip from Austin to Houston last month. Since I acquired the car it has seemed down on power and exhibited unusual idle issues (chuffing, stumbling sound that cycles almost like a thermostat) when fully warmed up, along with some shifting issues I'll address in a separate thread. The throttle response at low RPM is as dull as a butter knife, lacking in overall torque, and my original instinct (which turned out to be correct) was that the VarioRam system probably wasn't functioning correctly.

Some basics about the car and work that was done at the workshop in Houston last month:

• Mileage: 75,960
• New plugs, wires, rotors, caps
• New DMF & clutch
• New 1st/2nd gear synchro blocker rings (still not right)
• Refreshed shifter bushings (linkage and shift feel/precision are still crap)
• New engine mounts
• New alternator & power steering belts
• New PSS10s, lowered and aligned
• New Michelin PS2s
• Compression & leakdown test. Results: "excellent" on all cylinders.

After $20K of receipts, I expected the car to be running like a top. Once the shop sent me pictures of the condition of the wires, plugs, etc., I assumed that was the root cause of the performance and idle issues, or the latter by a failing DMF. It was not. The performance and idle issues persist, so that has sent me in search of vacuum and VarioRam problems in my garage.

Thanks to some of the excellent archived threads and Rennlist contributors here, I've been methodically working through the vacuum system with my MityVac and multi-meter and found the following so far:

1. First VarioRam actuator ignition "cycle" test: Upper actuators working correctly but will only cycle once or max twice on stored vacuum. Resonance flap actuator not working and covered in oil and grime.
2. "K shaped" vacuum distribution fitting collapsed. Replaced with new.
3. Vacuum modulator for fresh air flap on blower motor assembly will not hold vacuum. Ordered updated replacement.
4. Cleaned up resonance flap actuator, disconnected from switch-over solenoid, and pulled vacuum. Held vacuum with no leakdown for minutes.
5. Tested solenoid pigtail, getting 12 volts. Switched resonance solenoid with known good solenoid and tested again. Resonance flap appears to be working properly? (See video)
6. Second cycle test: all 3 actuators now cycle on ignition key on stored vacuum 6-7 times easily.
7. Per the factory WSM VarioRam test procedure, attached MityVac vacuum gauge to the fresh air flapper vacuum line and started the car to build vacuum. With engine running at idle car pulls a steady 20-23 inches/Hg on the gauge. When shut down, the vacuum holds for awhile but steadily bleeds back down to zero over the course of a few hours. Unfortunately that MityVac gauge is not accurate enough to measure a 0.02 bar drop in pressure over 3 minutes, per the factory test protocol.

Questions I'd like get opinions on:

1. Based on the above behavior, do I now have a healthy vacuum system or is there more test work to do? What would you test next from here?
2. What is a normal overall vacuum "leakdown" with engine power and ignition off? Is the behavior I described in #7 above normal or should that vacuum resevoir be holding stored vacuum for much longer/indefinitely?
3. I searched, but does anybody have a good smoke test protocol? I've thought about pulling the vacuum distribution fitting off the check valve and connecting a smoke tester there and also at the brake booster. Good idea, bad idea? Anywhere else?

Resonance valve after solenoid repair/replace: Hot idle behavior:

Thanks in advance.

Floyd540

Congrats on your new to you car. When you get the issues sorted out, you will have many miles and hours of pure enjoyment ahead. As to the current condition, everything that has been done has no effect on the poor running condition you are describing except for plugs but I don't think so since it is a twin plug ignition. What all of these cars have in common is that all the rubber and plastic parts are almost 30 years old and they have aged out. (think what 30 year old tires or fan belts would be like.) One area that gets overlooked is the rubber intake manifold boots that are held on with hose clamps. . They fail by cracking and creating a vacuum leak that can start out by being small or so large that the car will not run. People will spend a lot of time chasing down all the vacuum hoses and devices but the boots seem to get overlooked. Not saying this is the real current problem but the boots need changing anyway as they are shot.
Others will have better info.

Cogito_Ergo_Zoom

Thanks, I'll add those to my list of things to check as well.

pp000830

Hi Cogito,
Looks like you have done a good job sorting out the car. Many times the vacuum actuators are not in good condition as you experienced. The diaphragms in them were originally black rubber the replacements are clear silicone rubber and much more durable. The 2nd video of exhaust sounds sounds rather normal to me. A 993 does not exhibit a perfectly smooth exhaust rumble at idle. If you haven't cleaned out the Idle control valve with a little spray carb & choke cleaner doing this can smooth out the idle to some extent. When the valve is connected and operating it has a distinct vibration to its body.
I would not worry about the loss of vacuum when the car sits too much. As long as it builds a good vacuum while running, I would think, this is all you should be concerned with.
Enjoy your new ride,
Andy

Cogito_Ergo_Zoom

Thanks, Andy. Many of your posts on other threads have been very helpful in the troubleshooting process. I did further testing of the vacuum system last night and I think I found what I'm hoping is the final problem. The check valve that connects to the vacuum distribution fitting will not hold vacuum and will slowly leak completely down and drain the reservoir in about an hour. I'm also getting a constant stream of fresh air through the cabin AC vents, even with the fan on 0 on the CCU, so I suspect there is still work to be done.

I tested the VarioRam multiple times and it can be cycled with the ignition switch at least 6-7 times with all 3 actuators functioning correctly now, so as you said it's probably not critical but I'm going to replace that check valve anyway. I plugged the fresh air flapper vacuum line last night and took it for a test drive and it's running like a top now. All the low-end torque, mid-range, and throttle response it was missing before is there now.

I know these things don't idle like an inline 6, but I'm going to finish up the vacuum work, clean the ISV, and see if that doesn't improve the situation.

71-3.0-911

If you can cycle the actuators that many times without starting the car, I doubt that your issue is a vacuum leak. ISV is a good call next.

CosmosMoon

I agree to check the ISV - it's a PITA to get out if someone hasn't come before you and switched around the clamps because the clamps can sometimes be upside down on the hoses and difficult to reach (set them up with all screws on top facing you before putting the ISV back in). You'll find threads on it here for getting it off - once you do it a couple of times it's easy. I soak only the very end of it - the end that the hoses connect to - over-night in kerosene (or similar). Don't soak the electrical part
If you hold it and wiggle rotationally very quickly (think the motion you make when revving a motorcycle - but faster - or like one of those drum-toys with the two ***** on strings that you spin w two hands), you should hear the flapper inside clicking back and forth. If you don't hear, it definitely needs a clean - if you do it hear it then it still might need a clean!

That occasional ticking sound in your idle video is a little odd though.
.

Cogito_Ergo_Zoom

Yes, I just took a break from wrestling with it now. I didn't have a problem loosening the hose clamps and I have it nearly out of the flange that it sits in, but there doesn't seem to be enough room to fully clear it and it's jammed up right against the VarioRam actuator now. Careful about the rear hose and bending the metal pipe out of the way too much as well.

Im sure it's just a first time thing but this feels a little bit like one of those "trap jobs because of the lack of working room.

Worst case scenario I suppose would be to loosen the motor mounts and drop it about an inch and that would give me all the room I need.

Cogito_Ergo_Zoom

Finally freed it. It was pretty gunked up but not terribly so. Cleaned up pretty well with carb cleaner but decided to let it soak in mineral spirits overnight.

pp000830

Hi Cogito,
Sounds all good.
The fresh air servomotor is usually the first to fail where the fresh air vent in the hood may stay open. When the servomotor starts to draw too much current or fails to operate at startup testing the CCU shuts it down and ignores it. On the upside, it is the easiest one to replace the top center under the plastic shroud below the windshield in the frunk. If it still turns at all the easiest way to get it out is to release the metal plunger rod from its clip that holds the arm to the plastic actuator lever and if necessary turn the ignition on and attempt to cycle it so its arm lines up with the slot in its mounting point allowing one to remove the screws holding it and lifting it out. Just because it moves doesn't mean it works properly. The rebuild kit comes with a new retaining clip for the arm if the original one falls into the abyss. Also a failed actuator will show up as a fault with an OBD Code reader that can access the HVAC module.
Check pricing on a new replacement. If it is more than a couple hundred dollars you can consider the rebuild kit discussed below to save some coin:


See the below pages:
https://993servicerepair.blogspot.co...ditioning.html
and
https://993servicerepair.blogspot.co...ning-hvac.html

Best of luck with this.
Andy

guards red

Hi,

One thing worth checking if you have a slow vacuum decay on your 993 is the valve at the back of the engine behind the blower motor. Back there is a zinc coated plate that supports the two knock sensors, the crank position sensor, the emmissions control valve, the brake vacuum for the servo (only on two wheel drive cars) and the main vacuum feed for the various vacuum actuators. This latter one is the one you need to check. It is connected to the vacuum system by the "K" piece you have already replaced, one of the branches of which is connected to the vacuum reservoir in the left rear wheel arch.

The valve is the piece on which the "K" distribution pipe is attached and has a barbed pipe fitting. The valve is a one way valve allowing the engine to supply a vacuum that is stored in the vacuum tank. The valve allows that vacuum to remain once the engine is turned off. A slow leak here will see the vacuum disipate. Note also that the vacuum tank has an elbow fitting that can also leak. You will need to take the door side wheel arch liner off to check it, the tank is low down in the area that the oil tank is on the other side.

Hope that makes sense.

Regards
GR

INTMD8

Try running it on each distributor separately. Maybe the belt has slipped/broke.

Also would verify firing order is correct. When I bought my car the plugs/wires had been done previously by a shop and two of the wires were swapped.

Cogito_Ergo_Zoom

Thanks, @guards red. I had found one of your earlier posts and checked it earlier this week and it is steadily leaking down. I've spent more time troubleshooting and driving the car this weekend, and the VarioRam is working fine now in high vacuum situations after changing the faulty changeover solenoid valve & the distribution fitting, but, as you pointed out in that thread, in sustained full throttle driving the symptoms return when the reservoir is exhausted. So the check valve is definitely going to have to be changed, only question is do I try to do it in situ or leave it until I bring it back to the shop that did the original work.

I also got the ISV cleaned and back in the car. Using a little Super Lube synthetic grease on the gasket and inside of the hoses made the reinstallation a cinch compared to getting it out. It definitely helped some aspects of the idle, but the problem is still there, strong enough to shake the motor pretty strongly in the motor mounts intermittently. Again, this seems to happen most noticeably when the engine is fully warm.

That led me to connect a vacuum gauge directly to the manifold port, and what I observed has got me a little concerned. Vacuum seems very low at about 11"HG and there is rapid flutter in the needle. Vacuum increases to over 20" when I raised and held the RPM to about 2,500 and the needle steadied. On a "normal" motor with a standard intake manifold, that would lead me to suspect badly worn valve guides or some other valve timing issue...

I realize the VarioRam system may be unique and standard diagnosis rules may not apply, but 11" seems very low and I haven't been able to find any information on what's a normal reading directly at the manifold port? Any expert feedback on what a stock, healthy 3.6L should be exhibiting would be appreciated.

Video of the vacuum gauge reading:

Cogito_Ergo_Zoom

Thanks, Andy. Spent some time going through the rest of your test protocol this morning and I'm glad to report, other than the previously mentioned bad vacuum actuator on the heater blower assembly in the engine bay and probably the fresh air servomotor in the front, the HVAC system seems to be operating normally. I can hear the recycled air vacuum actuator operating and both sliders direct the air as designed.

Cogito_Ergo_Zoom

I checked the coils last night and both are fine. The car will run on either distributor. I haven't double checked the plug wiring order, but I feel like this would be triggering a CE light and the car, other than eventually running out of VarioRam vacuum because of the faulty checkvalve, is otherwise running smoothly at high RPM, no backfires, etc..

Next step I plan to take is pulling the MAF to clean/test and then smoke test the intake manifold while it's out. That it's only pulling 11"HG at the manifold at idle just does not seem right to me. After that I'll check out the O2 sensors and then fuel system. I started preparing for that by running a bottle of Techron through it last night.