Startup idle rpm all the time (1977 2.7 CIS)

[HenrikL]

First some background: I bought this car a few years ago. It was running, but the idle varied between 900-1500 rpm. The PO had lots of trouble getting the car through the annual environment and safety check, because the CO level was too high.

During my rebuild the long block has been rebuilt by a reputable shop and I have replaced a cracked air box as well as all rubber fittings, gaskets and hoses in the CIS.

Today it was time to start the engine for the first time after the rebuild. The car starts easily and idles at 1900 rpm. The time passes and I see and feel that the engine warms up. However the idle stays at 1900 rpm. After about 15 minutes at 1900 rpm I turn the engine off to change the oil.

Where do I start tracking the high warm idle problem? I cannot adjust the ignition until I get the idle to 900 rpm and the mixture and idle bypass screws are still as set by the PO (possible to compensate the cracked air box).

Have searched in the forum and found lots of high idle threads, but no one like my problem where the idle stays at the startup rpm.

[redstrosekNic]

I would try adjusting the idle using the idle screw... If you're concerned with re-setting the screw to where it is, just keep track of how many turns you turn it. If you can turn the screw in all the way without affecting the idle, you know you have a large vacuum leak. You really should have the CO checked with a meter to make sure that's correct before you run the car excessively. Good luck and keep us posted!!

BTW...I learned from this forum that it takes a few turns to affect the idle on the early CIS cars using the idle screw. Don't expect a difference in idle right after a quarter turn.

[Walter_Middie]

Typically if your car had an air leak, someone would have richened the mixture to compensate. This makes the idle OK, but high CO (running rich) at all other RPMs. Now that you have fixed the air leaks, it is probably running rich at idle too. There is an air screw to change the idle - turn it in (clockwise) to restrict the air flow and reduce the idle speed. There is also a small 3mm hex head screw that changes the mixture at all speeds. There are threads on here on how to set this by trial and error.

[Walter_Middie]

[HenrikL]

Thanks for the help! Is there any "default settings" for the mixture and idle adjustments? I'm thinking that it would be better to start from somewhere known, rather from the possible incorrect settings from the PO.

[redstrosekNic]

If you can read the stickers in the engine compartment, they should say... My '75 is about 950 rpm for idle, and the CO is 1.5%. I would run the CO a bit higher, though... Perhaps 2%.

[HenrikL]

Ok, some more work has been done on the car. I started by checking the AAR. It gets power and closes after a few minutes.

Then I started chasing air leaks. All hoses, o-rings and gaskets were changed when the air box was replaced. I sprayed half a can starter fluid over every part of the intake without any change in rpm.

Then I started turning the idle bypass screw. I could turn it in about one turn before if bottomed out on the compressed spring. No change in rpm. Turning it out made the rpms increase after about three turns.



I wonder if the throttle stop screw has been messed with? Is there some procedure to reset the throttle butterfly? If the throttle doesn't close then I guess it would be impossible to lower the idle, just like my car.

[Targalid]

In the Bosch CIS manual, it says there is a stop screw on the throttle plate which can be adjusted up or down to change the base position of the system. That may be what is needed. You should be able to see the adjustment screw by looking in through the air box. It positions the plate up or down in the main throttle body. The Bosch manual is worth printing and keeping close by. I keep my well worn copy along with Calling911's procedure for adjusting the CIS without gauges together to help me remember the details.

Bosch K-Jetronic Fuel Injection Manual

[T77911S]

make sure the decel valve is not open before adjusting anything else. it is that "acorn" looking thing to the left of the idle screw.
it works off of vacuum and is adjustable. hi vacuum opens it.

you said you checked for power to the AAR, but it is closing?

BTW, that screw on the throttle plate does kinda look like it has been adjusted. i dont think mine is run all the way in like that.

[HenrikL]

Originally Posted by T77911S

make sure the decel valve is not open before adjusting anything else. it is that "acorn" looking thing to the left of the idle screw.
it works off of vacuum and is adjustable. hi vacuum opens it.

Checked and it is closed!

Originally Posted by T77911S

you said you checked for power to the AAR, but it is closing?

Checked - closes completely after about 5 minutes when connected to 12V.

Originally Posted by T77911S

BTW, that screw on the throttle plate does kinda look like it has been adjusted. i dont think mine is run all the way in like that.

Success! The throttle stop screw was of course stuck and I had to remove the throttle housing and carefully heat it with a propane torch to get the screw to move.

With the screw adjusted so that the throttle closed, but the arm rests on the stop screw I started the car again .... and 1800 rpm idle. Bugger!

Looking closely I realized that the throttle linkage was too tight and prevented the throttle to close. I slacked the linkage slightly by the gearbox and voila - 1000 rpm idle.

I would not call the idle stable and the engine does not sound too happy, but now I can at least adjust the ignition, CO-level and do such a basic task as check the oil level.