930 CIS Issue - Low Idle and Hard Cold Start

RarlyL8 · RarlyL8's Garage

Got a head scratcher goin' on here. A 930 engine was recently transplanted into an '84 Carrera. swap is complete and running but has CIS issues.
When warm the engine runs as expected. Cold start is difficult. The engine will crank much longer than it should and will belch a rich puff of smoke when it finally fires. The idle starts off at about 500rpm and chugs to 800rpm. The WUR checks out in spec through all conditions. I replaced the WUR with another just to verify - no change.
What could cause a LOW idle? The AAV is functioning properly. If you block off the AAV during the first few minutes of cold start the engine will die.
Every CIS problem I have ever encountered caused a HIGH idle, never a low one. Also, very important - this engine has minimal CIS - consisting of only the fuel head, WUR, AAV, and cold start valve. CO is an eye watering 8%, when reduced to the spec 3% the engine runs poorly.

Any thoughts appreciated, this car needs to get on the road!

RarlyL8 · RarlyL8's Garage

Have I stumped you all or are all the CIS guys too busy helping others?

beepbeep · 03-13-2006, 06:00 AM

Plugged cat? CIS-thingmajig plunger is binding? If car runs poorly @ 3% CO it means that something else is bad.

Check system and control pressure, then check if barn door is moving freely, then reset CO @ 3%.

Wideband lambda is good for this kind of things.

Hladun · 03-13-2006, 08:48 AM

Air,fuel and fire; that's what it takes. Seems like you have fuel. How's the ignition system? How does it run when warm and/or revved? (Sign of ignition problems) That leaves air...air leak, something blocked? You've taken off CIS parts, is the plumbing correct? I don't have a turbo, but I think it should idle 1,500 to 2,000 cold.

Huh · 03-13-2006, 08:56 AM

How is the thermo time switch looking? Is it hooked up?

javadog · 03-13-2006, 09:19 AM

The engine is probably just pissed off that you installed it in a Targa chassis.

A few questions:

What year/engine type did you use?
Did you change out the fuel pump?
Did you retain all of the stock ignition components?
Have you checked to see if the retard/advance at idle/off idle and the advance when cold is functioning correctly?

What, exactly, did you remove from the engine?

We'll get to the CIS in a minute.

JR

RarlyL8 · RarlyL8's Garage

Thanks guys, here's what we have:
- Car runs properly but rich when warm. Idle's at 1000rpm and smooth to redline under load.
- No cat, Euro exhaust
- Air plate moves freely
- Control pressure is within spec
- Thermol time switch has been removed
- Thermol time valve has been retained
- Engine runs poorly if set to CO of 3%
- Timing is set at 5*atdc, no other ignition checks performed.
- Engine is '78 49 state 930.

This engine is nearly identical to the engine in my car. My engine has even less CIS equipment on it and it runs perfectly. I simply don't understand what could prevent the engine from idling up like it should when cold. The AAV is functioning as it should, if you block it off the engine will die. The idle screw is full out. It acts like it is not getting enough air bypassing the throttle when cold.

javadog · 03-13-2006, 09:58 AM

Is the system pressure within spec?

The ignition timing should advance about 15 degrees when first started from cold, if the thermal time valve is operating correctly. I'd check this first.

Have you made sure that the distributor internals are well-lubed and it can achieve it's full range of advance/retard?

JR

Huh · 03-13-2006, 11:38 AM

Did the car run fine without the thermal time switch before? The thermal time switch should give the enrichment for cold start until the lambda sensor gets to temp then it operates via the thermal time valve.

Paulporsche · 03-13-2006, 11:47 AM

have you checked to see that the AAR is opening far enough? Staying open long enough? Have you checked to see that the sensor plate @ rest is @ the proper height?

WERK I · WERK I's Garage

Quote:

Originally posted by RarlyL8
The idle screw is full out. It acts like it is not getting enough air bypassing the throttle when cold.

Why is the idle screw full out? I think the system is out of wack. Someone may have had a AAR problem in the past and got around it by closing the throttle body fully and using the air bypass circuit on the AAR for hot AND cold idle. When the new AAR was installed, the idle problems you just described reared its ugly head. When the car is fully warmed up, plug the AAR and adjust the idle adjustment screw until you get the desired idle speed(950 plus or minus 50RPM).

Paulporsche · 03-13-2006, 02:00 PM

Oops, Werk1, I see he has no AAR, only an AAV. That may be the problem right there, even in AL.

I was recently having cold start/warmup issues, even though the CIS seemed to check out. Turns out I had a broken head stud that was causing a lean condition until the car warmed up.

WERK I · WERK I's Garage

Paul,
Good catch. Thanks for spotting that.
Without the AAR, it makes it even more difficult to get a good idle on a cold start.

Tripster · 04:21 PM

Just got home and by-passed the thermal time valve, NO change, car still turned over several time thin chug a lugged to life. I killed it and pulled a plug. It was lightly coated with black sutt, but not enough to kill it, im sure as it warmed it would burn right off, it was not that bad. Hot plug cold plug??? # DENSO W24ESR-U
Also, the plug that I removed has a .023 Gap.

RarlyL8 · RarlyL8's Garage

System pressure is within specs.
The dizzy has not been checked out (yet).
This engine was purchsed recently, we know very little about it. I have a call into the mechanic that delt with it previously.
The AAV is functioning properly.
The idle adjustment screw is full out so that we will know when the problem is cured (and adjust it back).

This engine is very similar to my own, one difference being that mine has even less CIS equipment on it. In climates that stay at or above freezing you don't need an AAV. All I have on my engine is a cold start injector and a WUR. That's it, and it runs perfectly. It could be that we were too quick to blame the CIS for this problem and it is ignition related. The dizzy and spark plugs will be checked next. I also am not fully convinced that the cold start valve is functioning properly. A full time leaker could sure cause the symptoms we are seeing.

Here is a picture of my engine. Note the absense of any time switches or auxiliary air devices.

Tripster · 03-13-2006, 05:33 PM

Just ruled out cold start valve, I found a fitting that fit the fuel head and plugged it off. Car ran the same, chug a lug.
Also, plugs are on .024 not .023. I did clean them and put them back in,, no change.

Tripster · 03-14-2006, 05:07 AM

I am not one to waste allot of time on a problem like I have on my hands right here, this has to be something very simple. So what I need to know is where can I get the information on this CIS, how every component works and when it should work. Some times you just need to go to the basics. Symptoms are as follows.

1. Very hard to start, then it chugs for 2 mins then clears up.
2. Will idle up at all, 5-6 K cold, then 1000 K warm
3. Runs great when warm.
4. Co has to be @ 8%, @3% it runs terrible when warm.
5. Drinks fuel, 8-10 miles per Gallon
6. Pissed off Carrera,,,,, and owner.

javadog · 03-14-2006, 05:53 AM

There are a number of books on Bosch injection systems. There is also a bit of coverage in the aftermarket (Bentley and others) books on the 911SC that might help. The factory manuals have some info, if you're willing to wade through them to find it, and the books Porsche publishes at each model year to describe technical changes to the cars are also helpful.

For the idle problem, I still think you need to verify the correct operation of the distributor.

The next thing I'd check for the hard starting problem would be the resting position of the metering plate.

Lastly, I'd start checking for intake leaks.

Perhaps it is also worthwhile to figure out if some of the major components (fuel distributor...) have been changed in the past and the wrong part put on the car.

JR

Paulporsche · 03-14-2006, 08:54 AM

Tripster,

There is a lot of info here via the search function on CIS. Also try Jim Williams. He has a great site full of descriptive CIS info. The Bentley manual also has component descriptions and specs. Typical CIS problems include WUR, AAR and decel valves being out of spec, fuel and control pressures incorrect, vacuum leaks, clogged fuel filters, plunger and sensor plate incorrectly set, bad fuel accumulator or check valve, clogged fuel distributor or injectors. Other non injection problems typically include CD/coil, plugs, wires, cap, rotor and points (where applicable). Later years can exhibit problems w/ DME and O2 and other sensors.

Finally, as iI mentioned earlier, I had a poor start/warmup situation recently which seems to have been caused by a broken head stud.

Tripster · 03-14-2006, 10:31 AM

Paul, thanks for that info, actually Jim Williams lives here in Huntsville, I talk to him a few weeks back before I had this problem. I am going to check the Distributor tonight to make sure it moves free inside. I think after that I may pull the Fuel head to see if any thing is going on there. After that, I may pull this engine out of the car, have the body painted and think about a Carrera intake. I am frustrated enough right now I can justify scraping this CIS system. I would have thought Porsche could have done a better job than come up with this set up.