1983 944 surging idle

[Magic944]

My 83’ 944 has had a problem where it surges a few minutes after warming up/driving around. It is only noticeable at idle or moving very slow and also sometimes goes away. I’ve seen that a possible reason for this could be the DME temperature sensor, but I have not found very much info about replacing it. Does anyone have any ideas on what else it could be as well as how to change the Dme temp sensor?

[944 Ecology]

As always, Clarks Garage to the rescue:

https://www.clarks-garage.com/shop-manual/elect-19.htm#dme-temp

[Magic944]

Thank you so much

[walfreyydo]

Surging idle not likely related to DME temp sensor, and before changing it you should probably test it first.

More likely you have a vacuum leak (or issue with ICV) as mentioned in Clarks Garage Engine Troubleshooting
https://www.clarks-garage.com/shop-manual/ts-01.htm#idle-surge

[OK-944]

I had exactly this issue on my '87NA - with the culprit being a poorly functioning ICV (Idle Control Valve), which I believe is similar to the ISV (Idle Stabilizing Valve) on your '83.

On my car this is basically a stepper motor which works both electrically and in conjunction with the pull of negative (vacuum) pressure from the intake manifold to which the ICV/ISV is attached, via. a vacuum hose.

I can test the ICV on my car by disconnecting its electrical lead and jumping the two outer contacts (there are three total) to a 9 volt battery and listening carefully to ascertain that the rotor within flicks back and forth, otherwise the ICV itself might be the issue...and if so it is possible to remove it, bend some tabs to pop its cover (don't lose the O-ring!) pull the rotor/stator assembly out and clean this up, also possibly bending the three brushes inwards to refresh contact with the inner rotor.

Reassembly can be a bit frustrating as you will be working against some pretty strong magnets within the assembly to get things back together. Don't forget to reinstall that O-ring (check it first for cracks) as this is needed to hold vacuum, and re-bend the metal tabs and you're good to go.

But if the ICV does pass the 9 volt battery test, the problem likely lies in the "S" shaped vacuum hose, either in its connections or, more likely, that it has developed cracks...which is actually pretty common as the whole assembly is located more or less out of sight underneath the intake manifold, which also makes it a bit tricky to either service in place or remove - without removing the intake manifold first.

Such a check and removal of this valve with the intake manifold in place is possible with the aid of a long screwdriver or hose clamp removal tool, a good flashlight, and a well rounded vocabulary of colorful language.

[grendiers]

I had a similar situation, but surging at startup. After a couple years of frustration, I checked the throttle plate. It was fully closed. I adjusted it per the factory specs, and no surging! 1989 951. Not sure the fix is hiding some underlying issue, but I’m going with it!

[Monkey Wrench]

it would be crazy to suggest an aftermarket supplier would charge more for a "Porsch" part than another vehicle if the part is the same but you may find some of those ICV's are identical to those used by Volvo of the era. If you can ID yours and compare what it looks like to Volvo, it may bring other parts sources to light, perhaps used parts.

rubber hoses that have anything to do with recirculating crankcase smog have a shorter lifespan due to rubber rot caused by oil etc. oil makes rubber turn to mush over time.

[Magic944]

Thank you all for the ideas. I’m leaning toward the Auxiliary Air valve (early car ICV) being the problem. I currently don’t have 9v batteries to do the test Ok-944 mentioned, but Clark’s garage has instructions to clamp the vacuum hose leading to the intake manifold.. when I went to do this the hose was very stiff and I’m not sure how I would go about clamping it. Anyone done this type of test before, or have any ideas?

[OK-944]

I have a hose clamp that's basically a pair of Vice-Grips but with thinner, "soft" (rounded, non-toothed) jaws. Most hardware stores and some auto supply shops should have these.

But if that hose is old it may also be very brittle...which in your case I suspect as you'd said that it is "very stiff." So I'd suggest first getting a 9 volt battery and doing that test before messing with the hose.

Another approach would be to simply remove the intake manifold and replace one or even both hoses underneath it, and also test the air valve and try to fix it if its wonky. While these valves are a bit pricy to replace new...you can either look for a used one - or, if I'm not mistaken, I believe that there is an air valve made for Audi which may work at less cost...but someone else here will know better than I.

If you decide to remove the intake manifold...just make sure to get yourself a set of gaskets for it ahead of time...otherwise you might be tempted to just reuse the old ones if they "look like" they're in good shape.

Finally, removing the intake manifold means that you'll be either needing to at least contort your fuel hoses or I think in your case also disconnect these as in your car they run over the manifold if I'm not mistaken. At any rate...if your fuel hoses are as old as your car, you may discover at this point that its time to replace them.

Even better...if your fuel hoses are as old as your car - take advantage of the fact that you'll be disconnecting them - and go ahead and replace them. Believe me, you'll be glad you did! (A great resource for top quality 944-specific hoses is Len Cummings, who frequents this forum).

[Monkey Wrench]

I suggest sourcing the hoses then bench test the ICV. If the hoses are hardened up its also likely there is a big hole in a spot you cant' see. It might cause thing like the motor mounts to degrade if it's barfing up crankcase fumes. the hoses might be radically different in price depending on the source, Ive never found a very complete rubber kit for the whole car but I'd look around, You may find silicone hose kits. some do the smoke test to look for leaks, that might be a good idea too.

my 88 ford van has a similar issue i think the ECU isn't sensing the temp correctly so it stalls thinking it's warm when it isn't. When warm it's fine, I know its all different but I got similar advice to clean the throttle plate area for that vehicle.

what I did was ordered about 10 feet of some various fairly heavy duty rubber fuel hose sizes, I figure I can check when I get in there and if they fit , great and if not then I can look for metric sizes. I dont mind having a little selection. I figure the heavier fuel rated hoses are going to be ok for vacuum, might be a bit thicker walled. the hose and fitting retailer said something about "fuel hoses for marine applications"..

[Magic944]

I think I’ll end up doing the battery test just to be safe. I’m not completely sure if the hose is hard to clamp because it’s brittle or more because it’s a 3/4 inch hose with relatively thick walls? I figure that if the problem isn’t the auxiliary air valve then I’ll look towards the hoses.

[Magic944]

When you connected the 9 volt battery did you just use a snap connector?

[walfreyydo]

Alligator clips on the prongs of the connector. You should hear an audible click or feel movement within the solenoid. Sometimes easier to remove from the intake first and test on a bench. Clean if necessary so you restore movement (these often get clogged with gunk - carb cleaner works well).

[Monkey Wrench]

a couple of small wires from your battery will provide 12 V, The 9V battery just a handy source I think..
I'd just check to make sure you have your polarity etc correct.

stubborn hard old hose. try a squirt bottle with detergent and water, wet it down and then when you want to pull it off TURN it first. once the soap gets in there you should be home free. soaping or , less graceful but, spitting on hoses helps to get them back in too.

the soap test is how a ( gas) welder checks to see if his hoses are tight and not leaking too, so if it has pressure, not vacuum, the soap test can detect a leak, if it leaks you' ll see bubbles. they just fill a bottle with a bit of windex or dish soap and the rest water. Remember once I forgot to and saw my regulators light up, good think I looked up when I was grinding and saw it in time.

If you want to study it in operation you might use thin wires and get them to connect as well as the standard connector, then hook up a small watt test lamp in parallel with the valve. then you can see when it's on or off and if there is any significant change in voltage you'll see the bulb glow brighter or dimmer. you can use a meter but sometimes a little bulb can sit there connected and be studied more easily. If it's a very sensitive circuit then the bulb can cause issues because it draws power and hooking in parallel lowers the overall circuit resistance. It might not work well with a timing position sensor or a O2 sensor but i think this is just a 12V device..

If I want to monitor spark I just put one across the primary of the coil then you see it flashing when its cranking or idling , proves you most likely have a spark.
as the primary basically gets switched on and off to generate the high voltage spark.. You can see the little test light sort of blinking in unison. It is very easy to clip a small bulb across those two wires on your coil.

sometimes people are mystified and think they have spark or don't , or suspect the spark is intermittent.. The reason I like that is then you can just watch the light if having start issues etc.

I like to add a little bulb to the fuel pump circuit, light is on, so my fuel pump has power, good to know, saves scratching your head.. a tiny bulb won't add a significant amount of resistance to that pump circuit.. one could likely add a few of them in specific places to monitor and make troubleshooting very simple
if you have a no start condition.

you can always add a switch so the bulb is not always on when you dont want to use it to test

another way about this is to simply make yourself an easy place to connect it and use the same bulb . a couple light bulbs in the trunk can do a lot and I hate keeping my expensive meter in the car, a bulb is cheap and very small and light. easy to understand , easy to monitor over time. if you get stuck on the road you might pull out the glovebox bulb and use that , like you are Macgyver ;-)

[Magic944]

I have the battery and wires now. Does anyone know which side to hook the positive and negative clips to (as seen in picture). I’m also very new to everything and am wondering if the type of wire matters when doing this?

[OK-944]

On my '87NA the ICV has three contacts...and I use the two outer contacts. I'd guess that in your case you'd just use the two existing contacts - but maybe verify this first.

On my car it does not matter which battery terminal is connected to which ICV contact.

Two lengths of 14 or even 16 gauge single strand "project wire" with alligator clips at each end works great for this. Just clip one end of each wire to each of the ICV contacts, and then clip the other end of one of those wires to a battery terminal...then touch (don't clip) the remaining wire to the free battery contact and if all is well, the ICV will respond very "heathily." In other words, an audible sound more percussive just a light click. If you feel the ICV as this happens, you'll feel that there is definite movement on the inside.

If no response or only the faintest of clicks...the unit likely needs either a good cleaning or replacement.

But again...do verify the procedure for your (two contact) unit!

[originalowner]

The early car idle valve, called the Auxiliary Air Valve, or AAV, is completely different then that of the later car. The early car valve lets more air past the throttle to increase idle speed while cold. It contains a heater and bi-metalic coil that closes the valve as it heats up. I seriously doubt that a 9v battery can power the heater in it. With 12V battery power applied, it will slowly close over a few of minutes.

The later car valve is controlled by the ECU and switches open and closed rapidly to actively set the idle speed of the car. The ECU determines what idle speed it wants based on the coolant temperature.

[walfreyydo]

https://www.clarks-garage.com/shop-manual/ts-01.htm#idle-surge

[Monkey Wrench]

thin wire is ok to check the valve. bell wire is ok for that. you only need heavy wire to carry heavier current loads.
if you pull that rubber boot back on the wire there might be a place you can solder to where the wires connect to the terminals. If you solder some test leads on you can always just clip them off or short and tape up later. If you dont want to delve into the schematic try hooking your meter between negative battery post and either terminal and the one that reads 12 V is hot. the meter shoudl tell you if this is a constant hot or if the voltage is varied somehow.

you can disconnect the batttery and hook your meter from negative to either lead and if one reads o ohms or near that it is probably grounded. keep in mind things can be turned on or off by switching the ground or the hot and the DME may be switching the ground, Im not sure which way its wired.

if you connected a small light bulb , like one used in the dash or similar you might be able to see when the light is on and off when it's running, that visual may help understand better about when it has power and when it does not. you can do similar with a meter if preferred.

i suspect the thing has a coil of wire inside it that acts as an electromagnet so when power is applied it pulls one way. if the polarity is reversed to the coil then it would still energize the coil. you could also check between the two with a meter and read the resistance of the coil. you can compare to others. your meter can tell if it's open ( broken wire) or shorted, I think you can expect some resistance, exactly what , not sure but it would not be zero ohms or oen line but somewhere between. in other words some amount of resistance. I can't say offhand, it might be 100 to 2000 ohms, just a guess.. if you have a spare to compare to you can expect that to be similar.

I think from what is said it's either open or closed and not open part way based on voltage but could be wrong.. some might have 3 wires at that connector.. If you can check with a meter then youd see either a varying voltage or simply 12 V being switched in or out.

Id be careful about feeding power to the Wires or grounding them, You don't want to blow your ECU by doing something weird lie backfeeding wires from your battery..


I noticed in clark's it says you can feed in 10 PSI to look for a leak, I guess one might inflate a baloon and connect that, and if the balloon is full of smoke that might work as a poor man's smoke injector. Ive heard of vape pens used.

[Magic944]

Thank you all for the support. I ended up buying some smooth tooth pliers and clamped the line linking the aav to the intake manifold as said in clarks garage. That’s what did it. She ran like a beaut with it clamped. Now that being said.. the process of changing the aav. Does anyone know if it’s possible to do it without removing the intake?