I could not get the idle down below 1800, I took the advice from the excellent suggestions within 914world-garage and replaced EVERY gasket in the vacuum chain, including fixed a leaky plenum. """But mine looked so good - it can't be leaky! """ It was VERY leaky!

When I rebuilt the plenum (both sides of the support columns were leaky) and put it all back together, the resulting idle was way too low. I now have the reverse problem!

If I open up the ARR (remove hose) the idle is still low. If I take off the air cleaner and loosen the idle screw (all the way) still around 800-900. hhhhmmmmm.....

Throttle works, car will rev.
When driving the car it runs ok, however it does not have the power it used to have.

Engine is popping/missing, though the audio is not optimum, check out the video:

https://youtu.be/p5uM67DXJnk

Looking for next steps, what would you do next??????

Background; '74 2.0 all STOCK with 20K miles, I have rebuilt:

throttle sensor PCB
Throttle control - does not leak, very smooth control, set spec on the electrics.
MPS - tested and perfect
PCV - seems to work
Injectors - just back from Hurst injectors - all on spec
Distributor - clean and spiffy, advance works
plugs - new
AAR - tested and works
Computer Control Unit - I have 2, have swapped them and they both perform the same.
Flow Down - on spec
Dwell set
Timing set

Many thanks in advance

CTC911CTC

***********fixing my own problem:

https://members.rennlist.com/pbanders/idle.htm

“ My idle doesn't change when I open the air bleed screw. What's wrong?
Very lean idle mixture: When the mixture is very lean, the air bypass has no effect on the idle speed. Go to a shop and have your idle CO measured and set to spec on a shop-quality analyzer. “

Next step, Mr. Anders suggestions!

is the CHT plugged in?
you are still getting air in.
2.0 liter runs rich OOTB.

Here is how I figure it out.
Remove everything from the plenum except the hose to the MPS.
Tape over all the other holes, including and especially the AAR valve.
Now start it...
Assuming your timing is correct, you should have full control over the idle with that bleed screw now.
If not, its the MPS at fault...its the only thing you left connected to the plenum, right?

if you are good, then its just a process of elimination to find the fault as you add back on hose or system at a time.

rich

Dwell and timing done since the low idle raised its head? In what order did you do those two? If correct and all components of the DJet are correct I'd suspect the MAP sensor. If you have a variable resistor or potentiometer you could try varying the signal from the CHT to see if that helps.

**************PROBLEM SOLVED************

Picked up this car in October 2018,

I have fixed 100+ problems, some are listed above. I believe it is NOW ready for the road, it has not been registered since 1984.

When I pulled the Plenum (chasing the too rich issue) I was able to remove the CHT. Could not get a wrench on it prior. I replaced it. As I wrote above; after I got the fixed plenum back into the car, the idle adjustment screw had no effect. This according to the all knowing Anders, is the result of a car running too lean. which also caused the popping....

So I went back to the old CHT (I had not tested it, just changed it because of it's age and it is on near everyone's list of things to replace) and I found that it was open - No Good. Ahhhh, so this could be why the car is now LEAN!!!!!

Click to view attachment

I then went to the MCU and turned the dial from the all left position (I used to be chasing too rich as the result of the CHT) to something in the middle and now the car is running at what seems to be the correct mixture. No More Popping.

Changing the CHT if there are any rich/lean issues seems like a good place to start!

Next getting an O2 sensor from Mark Henry to vernier the mix-dial/idle-screw!

THANK YOU ALL TEENERS FOR THE SUPPORT!

Out of curiosity - what is the part number on the CHT that you took out?

I don’t know the part number but I got mine from Pelican Parts.

The car was stored in 84, with 20K miles, nearly everything in the car was original - I am assuming the CHT was original as well. '74 2.0L,
______ Porsche #______________Bosch #
'74____311 906 041 A_________0 280 130 012
'73____022 906 041 A_________0 280 130 017

I brushed the rust as gently as I could, here are some pics of the numbers.

Click to view attachment
Click to view attachment
Click to view attachment

Is that a "041" is see there?????? Not sure........

Looks like it _could_ be one of those?????

Did the new CHT sensor not work correctly? Or did you just put the old one back in to test it?

I took the old one out after I took the plenum out. At that point I was able to get a wrench on it and replace it. I had a few failures going on, vacuum was bad and a cht was open. Rich and lean at the same time!

So the CHT is just a thermister.

It is easy to check with a DVM and the corresponding temperature. The resistance values are on the B Anders site.

What invariably happens is that over time the ground connection gets oxidized or....the wire contact gets loose.

Without a good ground to the CHT the car will run like crap....or not run at all if there is no ground.

My quess is that the oxidation between the CHT and the head oxidized and when you broke it loose then put it back in you cleaned the ground connection up.

I think McMark was making one with a dedicated ground...I put it in my old car and never worried about it again. 914 Rubber might be making them now.

Test the old one anyway just to be sure.

Cutting a slot for the wire in the side of a deep well socket makes r&r a breeze. 0 need to take the tin, or anything else, off. Sockets are cheap. Time? Not so much.

In this thread there is a picture of me testing the thermistor Mr.! grin.. I was able to get the OHM meter to register metal-to-metal (base of the CHT thermistor) zero ohms. In the picture it is WIDE open! new one installed and working great,

Thanks for the help! car is running good, first time since 1984!