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uh oh.. ('76 deville EFI question)

Started by Hankk17, March 24, 2012, 10:45:05 PM

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Hankk17

I decided to finally look at my super fast idle problem on my '76 SDV today.  No matter where I would drive it - highway or just down the street, whenever I'd stop or attempt to stop the engine would race at a very high idle and would never kick down making it difficult to stop.  So today I decided to take a look for real and I discovered a potential disaster.. the idle speed valve assembly itself has actually split in half.  There's a metal plate on the passenger side of the thing that looks like its the other half of a microswitch assembly with a little shaft that something pivots on.  Well when I took the air cleaner off, that metal piece was just hanging over the throttle body... so I disassembled the valve and took that part off and put it all back together.  Thankfully things still ran OK.. so I pushed on and turned down the fast idle adjustment screw on the front of the throttle body and actually managed to retard the idle speed back to a reasonable RPM - ~800 or so.  I just got back in from driving it about 50 miles and so far so good.  ever since I've picked the car up I've noticed that it chugs pretty badly when I start it from cold so I'm starting to think this valve hasn't worked ever or at least since I've had it anyway.

So does anyone know where I can buy a replacement?  I haven't looked very hard yet to be honest but it seems to me that rockauto wouldn't stock something like this lol.  I'm also very seriously considering ripping all the EFI out and going back to a carb just for my own sanity's sake..

fun fun fun.

-Hank
Wherever you go... There you are

bcroe

I understand those valves can still be bought.  If not, I might have an
extra.  Plugging the hole would be a quick fix, but the engine might tend
to stall when cold.  Chugging sounds like a mixture problem.  That is
controlled by the ECU and the engine temp sensors.  Easy to test for
proper cold enrichment. 

Taking off the EFI works, but the conversion is involved.  Easier to just
fix it.  Bruce Roe   CLC # 14630 

Hankk17

just got up after a nice late sunday morning sleep-in and ran outside to turn the car over on a chilly march morning and sure enough I had to stay with it to keep her going.  So, I still think the valve was doing nothing but the high idle speed was what was keeping it running.. but I also hear what you're saying Bruce about swapping in the carb.  I have access to the parts and someone to help me, but I like the "unique" feature of having a '76 with EFI.  you don't see many around anymore that aren't sevilles.

So yeah Bruce - if you can put your hand on one let me know and let me know how much you want for it.  I did go surfing around last night for a new one and all I can find are ebay listings... nothing "new"

Thanks!!

-Hank
Wherever you go... There you are

jagbuxx #12944

Hankk,
My guess is that you may also have a fault with the coolant temp sensor. These act as sort of "choke" and signal for enrichment when cold. Once the coolant is warmed up and the car runs well would indicate this part as failing.
The car use 2 of them interchangebly, one for coolant the other as an air temp sensor. The part is also shared with Sevilles and other EFI Cadillacs thru 1980 when fitted with the 350 motor
They can be measure with an ohm meter. I have pulled many of them from junked cars through the years and when tested, about 15-20% are out of spec.
Make sure ou get either a '76 shop manual or at least the EFI supplement. The system is fairly simple by todays standards and as you note, it does make the car more distinctive.
I have quite a few them squirreled away along with other EFI parts and list them occassionally on Ebay.
Frank Burns #12944
76 Coupe d'Elegance EFI Galloway Green Firemist
70 deVille Convert San Mateo Red
61 Coupe Deville Bristol Blue
41 Series 61 Deluxe Coupe 6127D Black
08 STS 3.6 1SC  Thunder Gray
16 GTI Gray
03 T-Bird Black
16 Grand Cherokee Summit, Granite
19 Tiffin Phaeton 40AH
07 Corvette Blue
20 MB S450 White

"Whatever the occasion, there
is no better way to arrive than in a Cadillac.

waterzap

Leesburg, AL

Gene Beaird

Agreed with Jagbug.  Test the water temp sensor that's in the water jacket in the intake manifold.  The one on our 79 Seville was open.  I recently replaced it, and the car now starts and runs a LOT better cold.  Before, when I started it, it would take a couple of times trying to crank it over to get it to actually light.  Then, it would run for a few seconds, and die.  Now, while it still took a couple of times trying to get it to actually light, when it did, it stayed running, and the RPM eventually came down to near normal.  I think I have another issue with the idle speed control, they are problematic, the car is behaving a lot better now. 

Do some searches on this forum, as Waterzap, Bcroe and myself have had several of these conversations lately.

Gene Beaird,
1968 Calais
1979 Seville
Pearland, Texas
CLC Member No. 29873

bcroe

Looks like I have a good cold idle air valve, from the junk yard.  Not sure
which engine its from, but maybe its not that critical.  Email me to
arrange getting it to you.  bcroe@juno.com   Bruce Roe CLC # 14630