Idle Problems 1973 Volvo 1800ES

I am having the following problems with idle:

• After warming up, the idle is running 1000 rpm (specification is 900), and it surges or fluctuates between 900 and 1300 rpm. 
• If I take the throttle up above 2000 rpm, it will return only to 2000; that is, it will not return to 1000 rpm. 
• If I block off the idle air momentarily, it will go back down and run at 1000 rpm. 
• If I shut the engine off at 2000 rpm, it will re-start immediately at 1000 rpm, touching nothing but the key.  

Hopefully this link that shows the problem works:
studio.youtube.com/video/p3Qtj3VjAkg/edit

I have gone through all components settings and done all tests that I have capability to do,but ask me any specifics on this. 

I thank you for any and all assistance. 

Charlie

Hi Charlie,

I could not open your video. What I understand is that you have heavily fluctuating idle. High rpm comes from air not from fuel. Fuel can only bring down rpm if A/F ratio is too bad.

I found in Bosch service manual that warm idle shall be 900 rpm on engines with manual gearbox and 800 rpm with automatic gearbox. You have an idle-run adjustment screw that should allow you to bring it down to that value. Remember that car rpm meter is not exact.

Now the question is where your high idle of 2000 rpm comes from. It means that a vacuum leakage on manifold opens and does not close again. Candidates for such a bahaviour are:

1. Leaking vacuum hose on manifold - also the one to MPS
2. Brake servo
3. MPS itself with leaking diaphragm - did you do my vacuum leakage test on it
4. Manifold sealings
5. AAV loose - You can check by closing hose to AAV. That must not change idle-rpm on warm engine

Thank you for the quick reply. Sorry you could not open the video. I am able to, so I am not sure how to fix that.
I have done a vacuum leak test of the system with a smoke tester. The only leakage is very slight around the engine side of the throttle shaft. The AAV is blocked off fully. I have vacuum tested the MPS, but I will check into your method, which I have not looked at yet.