928ntslow

1982 Euro AT CIS 300hp car.

Of all my 928's, I have to say that this car is the most pleasurable to drive and is just solid with excellent power on demand...when it's warmed up.

That being said, here is the issue I need to figure out....

Car starts up on first twist nice and strong in the mornings. Idles solid and even. Drive about a mile and as it warms up, the idle surges, meaning it falls approximately 500 rpm's from normal idle while in gear and rises back. This only happens when at a stop whether in gear or not. I have to keep my left foot on the brake and the right on the throttle giving it a bit of gas to keep it from dying.

After the car has reached operating temperature, it idles smoothly again and does not die at a stop. Actually, it starts up fine the rest of the day and doesn't repeat the surging until it has sat overnight.

It was suggested that the AAV(Air Auxiliary Valve) is the culprit, but I have already looked at that. It just feeds air to the throttle body when cold and closes when warm. Works fine at the two extremes, but I don't know how it would affect the middle part where the idles surges.

Anyone dealt with this issue before on a CIS? I am sure it's an easy fix, just don't know what is causing it.

TIA

Dennis Wilson

Keith,

Have you checked the leads to make sure you are getting 12 volts to the AAV and WUR once started? If not, that could explain to eratic warm up. I would also check the ground(s) on these connections

Dennis

V-Fib

Yes to the above and don't forget to check all the vacuum lines.

SharkSkin

Keith, with CIS the most critical factors other than ignition timing are fuel pressure and vacuum. If possible, put a pressure gauge on the WUR and a vac gauge attached to manifold vacuum and watch them as it warms up.

If fuel pressure is stable(should change slowly as car warms up) then look for an air issue. For example, start the car in the morning and run it for ~10 seconds to get the juices flowing, then shut it off and remove the aux air line from the front of the plenum and block both the hose and the fitting where you detached it. See if the problem persists with this air circuit cut off. If it won't idle at all without this, give the idle screw on the front of the TB a couple turns.

If the fuel pressure swings wildly during this surge then you may need to clean out the WUR and the screen in the WUR line coming off the fuel distributor.

I know US cars have a thermal vac switch that can cause similar odd behavior near the switching point if the hoses are swapped -- kind of like the heater valve, it doesn't seal well if the flow direction is reversed. The Euros have a temp switch instead, on the small water outlet to the hot water valve on the rear of the passenger head. Just mentioning this in case the Euros have a thermal vac switch elsewhere.

My vote is AAV as well though; IIRC there is a long bi-metal arm and heater -- if this is cracked and flopping around it could cause the symptoms you describe. Also a cracked hose that sometimes seals itself can cause this symptom. Note that losing power to the AAV or WUR should not result in a rapid change in operating parameters. Both use bi-metal strips that ought to take a bit to change position. On second thought, the WUR may cool rapidly due to the fuel rushing through. Also check to see if your cold start valve is getting a steady 12V until the temp switch engages, if all else checks out do a flow test on it.

devilinblack

I know that improperly set idle mixture will cause surging and that this problem often becomes worse as the seasons change and the air becomes a bit more dense. I'm not sure if this would happen only when warming up though.

Here's a couple threads on CIS stuff with some good info.

http://forums.pelicanparts.com/showt...s+mixture+idle
http://forums.pelicanparts.com/showt...&highlight=cis

Might be worth looking into if everything else checks out okay.

jpitman2

I had a similar problem a year or so ago. Start fine, move off, stop at lights < 1mi away, surging, occasionally dying. At total cold start, the idle was lower than spec - under 1000rpm. I pulled the AAV, and tested it for full open by putting in the freezer - only opening 60%. I drilled out the rivets, bent something inside so that it was closer to full open at 0C, reassembled with M6 bolts. Now a really cold start will idle ~11-1200 briefly, and the surging has gone.
jp 83 Euro S AT 51k.

928ntslow

I probably should have posted the info below in my original post, but foolishly made the assumption that is wasn't necessary.

History
-pulled the motor and had the heads resurfaced due to to hard water and head gasket failure. Of course
all parts in the heads were checked and new parts replaced if needed.
-All new hoses and vac lines (including brake booster and check valve)
-Rebuilt the fuel distributor
-Replaced WUR
-12v to AAV, WUR and CSI checked
-All of the above is well functioning and triple checked. Gauges run at 3 points of the fuel delivery
system....all is well functioning.
-AAV is open at cold

That should answer a lot of the questions posted.

There IS however, a valve that I had disconnected when I did the motor refurb. Attached to the right side head is a 12v valve that receives fuel from the FD that ran to the WUR. I was informed that this thing is a hot start valve and is virtually worthless, so I had eliminated it.

Now where to?

Dennis Wilson

Keith,

Jon in AU had a problem with his hot start valve not long ago. I'm not real sure about how they function or if disconnecting them will cause a default problem. May want to do a search of the archives. He was able to find a replacement for his by contacting the guys at www.924board.org . Since it is a ROW only product, I'll please the 5th on this item.

Dennis

SharkSkin

Seriously, look at the internals on the AAV. Simplest thing is to take it out of the circuit as I described and see if the problem goes away. Also, how much vacuum do you have at the manifold? Can you check whether the car smells rich or not when it's trying to die(may need a helper)?

One of the biggest pain in the *** things about troubleshooting cold start/warm up issues with CIS is the time it takes to cool down for the next experiment. I feel your pain there, that's why I am suggesting things that will quickly tell you if it's fuel, air, or neither.

Also, you may have checked your fuel system with a gauge at some point in time, but my suggestion was to have it in place and observe it while this problem manifests itself. At the very least you can conclusively rule fuel in or out. You can do this test at the same time as blocking the AAV fitting on the plenum.

CSI may still be partially blocked... have you checked its flow pattern?

928ntslow

AAV is open at cold and closed at warm. I have checked it. Taking it out of the loop will cause the motor to not run properly. I have not checked it at warm since its closed any way.

No vac leaks. Not many vac lines to begin with on a CIS, all new lines. Line to HVAC is plugged....on the "+" side. All fuel system is clean. Checked this several times. no screens are clogged. CSI snaps open properly and flows properly.

As I had said, I was very thorough when I had rebuilt this thing.

This may help....

I recently went to have the car smog checked and it failed CO which means it may be running rich. Idle is about 1K when warm and the A/F mixture was swagged by turning clockwise until the motor just about dies and then counter-clockwise about a 1/4 to 1/2 turn if I recall correctly.

I could stick the gauges back on and see what happens at the WUR, but I know the FP and FD flow quite well. The flapper was cleaned well when I had the motor out. Without the FD on it will teeter with the slightest tap of the finger.

I seriously doubt having the HSV disconnected would cause any issue.

Sorry if it seems like I am being resistant to performing the checks, but I have been down this road several times since I have had it running chasing other previous CIS issues.

SharkSkin

I understand -- it's a pain in the ***.

I understand the car will not run properly with the AAV blocked off, probably at too low an RPM -- but if it still randomly drops several hundred RPM(or dies) like you're seeing now it will have been conclusively ruled out. OTOH if you don't see the RPM drop like this, you know to dig further into the AAV without having done more than remove one hose.

While your fuel delivery and pressures, AAV, etc. may be fine while warm and while cold, your problem is in an intermediate state and IMHO you need to try to troubleshoot while in that brief intermediate state. My suggestions above were primarily geared toward that end, especially the third paragraph in my previous post.

Basically, you've already had everything apart, I know you were very meticulous putting it back together. You don't want to touch anything you've put back together, that you "know" is right. Unfortunately, that's the nature of CIS. You have to open things up here and there to troubleshoot.

BTW, do you have a vac limiter? If so, have you verified that it closes completely and that the diaphragm is not leaking? I had both problems with mine(well, in addition to an EGR vac line issue), and the car would flub off idle letting the clutch out, as if it were not getting fuel. I'm not sure exactly how it would manifest on an AT, but it's worth checking.

Another too-obvious suggestion -- double-check your vac hose routing.

SMTCapeCod

Surging is a common indicator of the mixture being rich on CIS.
My car also has rebuilt WUR...I wonder if the warm up curve could be a bit too steep, causing it to be OK for start and warm running but too rich in the middle.

Of course, if the baseline mixture is set to keep the idle at 1000 rpm...that high baseline might skew the whole thing to run a bit richer?
I'd try to get it running well at the factory idle and see whether that helps things warm up in synch.
FWIW- that didn't cure mine, mine starts good, after about a minute goes through a half dozen or so oscillations before settling to normal again. No stalling (yet).

928ntslow

Yea Dave...PITA, but I DO appreciate all the suggestions! The fuel line fittings tend to get stripped inside and out if they are removed too often.

Not sure about eh vac limiter...never heard of it and don't recall ever seeing one. This is an ROW car and all that USDOT federalization crap was yanked off when I had the motor out. No air pump either on this engine.

I will do the check on the AAV...easy enough. Vac lines are routed properly.

SharkSkin

The vac limiter is shown for euro, illustration 107-05 item 21(PET). It's item 6 on the diagram below(from 78-80 tech specs book) and is called out for the M28/09 engine.

hupp

Keith,

Let me guess, you must have a stop sign about three or four blocks from the driveway where this happens. Right where the CIS is in some funky halfway " is it warm or not warm" mode. Your idle CO is adjusted too rich ..... it doesn't take much. I've experienced the same behavior with my CIS, leaning it out a bit cured my problem. Give it a shot, its easy enough -- lean out by about a quarter turn or less. Remember, go past the point you want to be and make your final adjustment to the rich.