CIS troubles...

Kanipso · 09-18-2005, 04:12 AM

I am having a problem with my 82' 3L CIS motor. When it's fully warmed up. (Oil is at 200deg or better) It likes to idle up on it's own.. If I leave the car in nuetral and blip the gas the engine will stick at 2000rpm on the way back down. If I drag it down with the clutch it will Idle at 1000rpm for a quite a while. This only happens when its warm. When cool it's crisp and always comes right back down..

I've done the obvious. New manifold boots etc... Could it be the warm up regulator? I am not running the 02 sensor either..

Ohh, it also does something else I think is strange. When Idling, I'll open the oil tank to check the level the rpm drops to ~600 and barely stays running. If I replace the cap idle comes back up to 1k...

What the he!!?

ejames19 · 04:34 AM

Hey Kanipso, welcome to the board. Need pictures of the car!! Anyway, first thing about your idle. Running your O2 censor in some cases solve idle hunting problems and after the car is warmed up I would count out your WUR, I am not the pro on this maybe someone else could jump in and help you out. Second, with the car running if you remove the oil cap the rpm's are going to drop and the car may shut off, that is a good thing it shows you have oil pressure, this is normal, be worried if when you remove the cap and nothing changes.. Hope this helps.

Kanipso · 09-18-2005, 04:49 AM

Here's a pic... It did the same thing with the stock exhaust and a working 02 sensor... I installed headers and exhaust and ruined the sensor in the process.. (smashed) It is mounted in the header currently but is really only pluging the hole.

safe · safe's Garage

Quote:

Originally posted by ejames19
Second, with the car running if you remove the oil cap the rpm's are going to drop and the car may shut off, that is a good thing it shows you have oil pressure, this is normal, be worried if when you remove the cap and nothing changes.. Hope this helps.

I think that is a common missconception. Its just an indicaton of a missing restrictor between the the airbox and oilfiller tube. I would fix the problem. Mine doesn´t drop in idle the slightest.

How stupid would it be of Porsche to make it normal for the engine to drop the idle when opening the oil cap when you are supposed to check the oil level at warm idle??

To the problem: Have you checked the "deceleration valve"? It could be leaking.
Check out this site: CIS primer

Kanipso · 09-18-2005, 06:11 AM

What about this? This sounds like it would cause the high idle after warm up... Thoughts?

Auxiliary Air Valve:
Provides bypass air around the throttle when the engine is first started. When the intake manifold vacuum reaches 5 - 6 inches, the valve closes. The closing is independent of engine heat. Part number 0 280 160 400 pulls in at ~8" vacuum. This regulator supplies air to the intake manifold during warm and hot starts when the auxiliary air regulator is closed. This was added in '76.

Failure mode: When not closing properly, can cause high idle speed , or idle speed to oscillate.

Kanipso · 09-18-2005, 06:16 AM

I think you got it.. The decel valve sounds like the problem. I'm going to disconnect it now and try it....

Kanipso · 09-18-2005, 07:22 AM

Ok I tested it w/ the decel valve disconected. No change at all. I guess it's possible the valve diaphram is ruptured thus always bypassing air?? Thoughts?

Gunter · Gunter's Garage

When removing the cap, it is normal for the RPM to drop ~100 or so, it has nothing to do with oil pressure, or any flow restrictor in the breather hose; it's a vacuum issue.
Porsche had to design it that way to meet emmission standards.
If you open the oil cap and there is no difference in RPM, it means that you have a vacuum leak all the time that is masked by idle/mixture adjustments to compensate.
AAR, or Dec. Valve, could be suspect or a sticky sensor plate.
Check the sensor plate and basic setting closely.
Do you still have the plug, or can you set your mixture with the 3mm Allen?
There are many SC's running with the OX sensor disconnected.

Kanipso · 09-18-2005, 08:49 AM

That's what I thought. Most SC's I know of are running without an o2 sensor. They run great. My car runs good too... just the annoying high idle.

I had the mixture adjusted when I did the exhaust. To verify it was ok I put in a new set of plugs last night. The olds ones looked good. Light brown color, no black deposits. So I think the mixture is ok.

Why is a replacement AAR so damn expensive??? $300 is crazy.. I can't even find the Dec. valve. Does anyone have a part #?

I don't really care about the rpm drop with the cap open... I can live with that.

Got to love the pcars... (no really)

Scott R · Scott R's Garage

I was just on the same wild goose chase as the one your on, got luck in that the other day the "timing" valve spring a huge fule leak. Anyway, with the timing valve disconnected my high idle went away, and now that its replaced a whole slew of weird idle issues have been solved.

It's something to check at least.,

Kanipso · 09-18-2005, 09:30 AM

Are you talking about the frequency valve? Pictured below? What happened when you uplugged it and ran the car??

Megasquirt is looking more and more attractive!

Scott R · Scott R's Garage

Yea that's the guy. As near as I know it control's the "warm pressure" in some way. So when my system would run under warm conditions this guy was letting to much pressure past. When I pulled his electrical connection it was like everything was on warmup.

When I plugged him in, the idle would climb on up to 2000. Then as I was driiving one day it busted and started shooting high pressure fuel out from where the plug attaches. Damn thing cost me just short of $200!

Gunter · Gunter's Garage

Normally, the RPM turns rough if you disconnect the Frequency valve by pulling the relay under the pass. seat. That relay is connected to the Lambda brain, it gets power from the same fuse that operates the dome light. The Lambda brain, and relay, gets neglected over time; you may find some rust on the connections, use dielectric grease. The duty cycle of the Frequency Valve can be checked but it is best left to a Porsche shop.
You can test the AAR easily. When cold, disconnect the outside hose and with a mirror look inside. You should see an opening shaped like a half-moon, that's good. Reconnect the hose and warm up the engine. Shut off engine, disconnect the hose again, use the mirror to see the inside. The half-moon opening should be completely closed. If it is, the AAR works. You can also take the AAR out and test it with a 12V supply but be carefull with the electric plug; it has a small wire clip to hold it in place. That clip has to be unlocked with a small pick.
I suggest that you get a Bentley manual, read it and get familiar with the CIS components and what they do, otherwise you are just guessing.
Also, to make room in the engine compartment, throw out the AC, cruise control and fan blower.
Unless you know your system, you'll have the same problems with Megasquirt. These cars are 25 years old and I am always amazed that people get upset when parts fail or complain about the cost of new parts.
Anyway, good luck.