1979 Eldorado - 350 Olds motor - fast idle problems

I understand this is a very old post but I thought I would answer a couple of the questions which seemed open:

• The large spring is what keeps the FIV (fast idle valve) open when the "Heater" is cold/ not applying pressure to close the valve. So yes the large spring is important. Gravity and vacuum would tend to close the valve and you would have no fast idle without the large return spring.
• I am adding a photo of the original coolant/air temp sensor. There are two and they are the same PN which is 1609968.

I'm also posting a diagram showing the FIV parts in the TB. The gap between the plunger and the "derby" is what allows more airflow and a fast idle. Once the actuator is heated the pin extends and it closes the gap between the plunger and the "derby" (valve guide). I didn't show the large spring but the post above shows it. I worked for around 2 years to finally come-up with a plug and play replacement. The other temp sensor in the photo is also my creation.

There was also a clip at the bottom of the plunger. That part is not important and some are discovered to be missing. That means either someone already removed it or it was ingested by the engine...

I plan to post a technical thread on this topic but the 70's EFI technology crosses engine types and Cadillac models so I found this thread while trying to determine where I should post the tech thread. In both of the parts I created I tried to really understand and correct common failure modes.

Scott

Hi CarScope,
There is a failure mode referred to in the "blue" EFI manual as a "latched" condition. It's that clip which can become latched but to be fair it needs to be inserted a long way and probably during assembly. A latched condition would hold the plunger into the derby so far there is no bypass and thus no FIV function even though everything might be ok. If the hat/derby is upside down (should have the taller end down and plunger should enter from the short side) it would cause the derby sleeve to ride higher up on the plunger and would likely eliminate the function as well (or even crack the derby).

On the misfire I don't know if you are aware of it but there is a Seville based website where all of the diagnostic trees are listed (I think the entire "blue book" is there). They're pretty clear and they direct you to the appropriate tree based on your main symptom. I think for misfire they suggest checking everything spark/ignition related first but if you are at a shop and you can check the fuel pressure easily you may want to check that. Here's the link to the Seville site:

Almost everything can be fixed and because a couple of us are trying to keep these things running they aren't crazy expensive because we've covered most of the bases. There's another member named Bruce Roe (a little more active on the CLC forum) who is a retired electrical engineer and he's a magician when it comes to the ECU's. He also suggests an external fuel pump relay. The pumps can take a lot of power and they route it inside the ECU (some are claiming the ethanol containing fuel is causing pumps to get hotter). As the pumps require more draw a common problem is burning one of the ECU pins and so the external relay prevents that. I did a write-up on my 79 Eldorado. I was able to unpin the factory connectors and make all of the connections within the existing plug with the exception of a ground. Here's the link for that thread including photos:

I do have some used springs, plungers and "derbies" so once you know what you wish to do just send me a "DM" (Direct message).

Scott
PS: The middle manual is the "blue" book.

One other simple thing to check is the coolant and air temp sensors. Sometimes they're a bit difficult to unplug but they are easy to test. You just need to know the temp and check the resistance. If the FIV was latched or otherwise not allowing bypass and especially the coolant sensor failed with too low resistance the car could be running pretty rich. I'll attach the resistance curve from the factory manual.

The sensor and FIV are quick changes. The external relay is more involved. I posted all of the info which would make it fast work on the Eldorado but Bruce mentioned something about the purple wire function being specific to the Eldorado. Probably the best would be comparing the original pinouts on the Seville to the diagram I posted.

Sounds like the owner is lucky he has someone willing to take the time to understand the car.

If the sensor(s) need changing, very common, I recommend Teflon tape. The torque is a little inconsistent in the FSM instructions (attached). I would describe it as snug but not overly tight and roughly 12-13ft-lbs; not so easy to measure due to location and wires though.

Scott

See diagram attached...
There are actually 3 coolant temp sensors but only one coolant sensor for the EFI. The EFI sensors are 2 wire. There is also a warning light temp sensor (single wire ~240F), a stop driving now sensor (single ~260F) and even a 4th which looks like a sensor but it's really a normally open switch/delay for the blower circuit. I wish Cadillac had offered a gauge package for my Eldorado.

Edit: To clarify the EFI air and coolant temp sensors are the same PN. I didn't count the air sensor in the total of coolant sensors.

Scott

The blower delay on the Cadillac has a single wire and grounds through the sensor body to intake. I also have a 1979 Toronado and it has a 2 blade connection located on the heater valve. So same body style and different idea for a basic function.

I'm not certain if they gave the Seville anything more than the Eldorado but the Eldorado has a speedometer and a fuel gauge (photo attached). It also has 2 lights for indicating good economy (green) and "lesser" economy (amber). Everything else is idiot light. I only discovered the economy lights when I was replacing a broken gear for my trip odometer. I checked all the bulbs while things were apart and the green bulb was blown. The dash was also nicely illuminated once all the bulbs were working again.

There was full gauge package for the Toronado which included coolant temp, oil pressure, and volt meter. Even the Toronado basic gauge package had a temp gauge.

Scott

These are for my '79 Eldorado from the electrical trouble shooting manual... if the wires are the same color these should help you.