Some quick history.

Got the car 2 years ago as a non-runner. It has been running well, based on what I know, for over a year. Starts first time and seems to run smooth. That said I have not driven it much, average once a month for short distances, up to recently as I have been working interior projects.

Yesterday I took it out for the Austin meeting followed by several other errands. It was in the low 90's and in traffic the temp gauge was nearing the second white line but the dual electric fans seem to be keeping temps under better control than the old viscous belt fan. A/C was on and working.

At the last stop I started the car and the idle was erratic and around 500 RPM. The engine did respond to throttle but when released again dropped so low as to almost stall. Normal warm idle is 800 RPM. I got it home by keeping the rpm up at stops with throttle.

I did notice fuel pump whine that I have never heard before and it cycled with the rpm but I thought it might be volatge related as my RPM.

Once home and after the car had cooled for a couple of hours it started right up as usual, warmed to 800 rpm and had no fuel pump noise that I could hear over the engine.

I have previously put in new fuel pump, filter, fuel lines, in tank pump and had tank out and cleaned.

I have yet to get around to putting a fuel pressure tester on the car so don't have any of those values.

Is this a pump issue, fuel pressure settings or something else?

 

If you find the answer to this one let me know. I have the exact same problem. It runs great if the ambient temp is about 84 or below. If its in the 90's, as you, it does the same thing. Once the water temp rises to around 185 on the gauge lookout!
Mine has been this way for about 3 years now...

 

I see that you're in an OB. Interesting that we have the same symptoms. Its probably 2 totally different root causes.

 

Seems like hot pressure is too high. Your car should be too early for the hot start valve.

Or else something is engaging that also causes a vacuum leak.

 

Sounds like to me a hot start valve and / or a Warm Up Regulator

that is engaging fuel into the intake long after it is supposed to back off

I was fortunate enough to get a new WUR and my 79 runs so much better

instant cold start and idle and also quick start when hot...

800 mile round trip to SITM and no issues

even got about 20+ mpg during the trip......!

Had tested the cold start before and it was OK...

Good luck......

 

Your 32v 5.0 is a totally different problem

Probably a ISV issue or temp sensor II

You may need to diagnose the problem with a Hammer device for a record of what is going on....

Someone else will chime in

 

I am leaning towards replacing the temp II sensor since it appears original.
The ISV is a bigger deal. Don't you have to remove the intake to get to the ISV?

 

To the OP: Do you still have the deceleration/ vacume limiting valve in place? I found that mine was causing strange idle speed issues that would come and go.

 

It is still in place. Can it be deleted? If so do you just block off the plumbing or does some need to be connected. I remember there being a few vacuum lines connected to the assembly.

Only thing I have deleted is the air pump and associated plumbing.

Does anyone have a theory of operation for early pressure CIS systems? I need to figure out what all the components are suppose to do to figure out what might be going a miss.

 

I have my CIS cliffnotes you could use. PM me your email.

Also, you could search CIS and WUR and get up to speed quickly.

 

Since you haven't run the car much, and before you dig in deep...

Run some Berrymans or Techron (highly concentrated in 2 or3 gallons of fuel) thru the CIS system, FP relay jumpered (car not running). Cycle it thru for 30 mins, rinse and repeat.

This is kindof a stationary fuel system flogging. You could do the same thing under load, with the same ingredients, while working you car hard. These CIS cars like a good flogging.

 

Jim
Shoot me a PM with your email address and I'll send you some good videos (3 big files) which explain it all. It wont' be able to send for at least twelve hours.

 

Here's one...

 

If the car still produces good power when asked, I doubt that its wur giving high hot control - this usually kills power badly. I would do the flush with Berryman's and see if that helps. I have 1 very strange fitting on mine, apart from the hot start valve. This last is a solenoid in the line to the wur from distributor head; its connected to a temp sensor on the head heater outlet, and its job is to dump control pressure when temp is sort of half hot, only while starter is engaged. My temp sensor went high resistance (when it should have been 0) once, and I had to replace it with a 944 unit.
The other thing is a multi pin cable plugged into side of the distributor head - when I got the car and had hot start problems it was disconnected , which improved when I reconnected it. Have never seen any documenation that describes what this does - pretty sure I dont have CIS-E, as none of the other parts of this are visible.
I try to drive mine at least once a week, but have missed out a lot - ran a bottle of techron in a fresh tank the other day, but I dont have any issues at all with the engine, even at second white line temps.
I have had a cold idle issue once which was the Aux Air valve needing some attention. Maybe check for hoses cracked/leaking, or the AC extra air solenoid failed - if AC was on at the time?

jp 83 Euro S AT 54k

 

You may be on to something with the fuel pump noise. The CIS system is very pressure sensitive. The wiring on the early cars is a little on the weak side. A common problem is the failure of the starter to turn over when the engine is hot. The hack cure is to add a relay at the starter to send more power to the solenoid. The real problem is the gauge of wiring going to the solenoid is not thick enough to operated the solenoid when temperatures get hot. Resistance increases with temperature so a wire that works fine when it is cold may be marginal when hot.

I found on my 78 the fuel pump fuse holder had been burnt and the juice going to the pump was too low. I by passed things to get the car running and later made some changes to over come the increased draw from an aging pump. Yes you replaced the fuel pump but you still might have a marginal current flow when the car is hot. You might consider a temporary parallel wire to the fuel pump. This will provide a better current path. If this fixes the problem then you can make the patch permanent.

Good luck