jwillman

Have not driven the car much over the last 2 months and noticed recently on one of the rare drives that my warm idel would occasionaly surge / oscilate between 750-800 and as low as 400. It would seem to run fine under power but come to a light and the idel would sometimes be stable and other times surge between idel setting and 400ish RPM.

Saturday it did it again so I adjusted the idle up and it seems to idle fine at ~1000 RPM.

Assume I am just masking an issue by setting idle higher so whats the proper fix? Am I just not driving it enough? Know the CIS does not like to sit.

The Forgotten On

It is probably a vacuum leak in the bases of the intake spider, had a similar issue on my L-jet 81. Got rid of most of the surging.

Check your plugs to see if any cylinders are running lean, that should at least give some clues on what could be wrong.

kawi825

I had a few intake runners that sucked the gaskets right I'm, had the same surging between 700-1000

Jetdriver69

I had the same thing on my 82 5 speed. Changed the old O2 sensor and no more surging.

The Forgotten On

He has K-jet so there is no o2 sensor.

SeanR

Best bet is an air leak. Always fun to chase down.

This one time, at band camp, the only time it would fluctuate was when the engine was real hot on a nice Texas summer day. Long story short, the air leak was one of the couplers joining the intake snakes to the main intake body. When it got hot it expanded enough that the rubber didn't seal it. A new runner boot and things were fine.

tailpipe

You need to adjust the fuel mixture about 1/4 turn clockwise. I find my cars surge lean when the temps are colder in the winter then I have to adjust it back in the summer. Welcome to CIS

R.Pires

Hi,

That's funny, I have a fluctuating idle but only with the engine real cold. When it starts warming up it stabilizes on 700/750.
Could this also be a vacuum leak? And why only with a cold engine?

Regards

PS: Does anyone has a vacuum diagram of a 83S Euro, mine that was supposed to be inside the bonnet as long gone and I can't find one anywhere! Thanks!

jpitman2

Surging cold sounds like a problem in the aux air valve , or its plumbing. To find an air leak , spray something lightly flammable (that wont hurt anything) on every joint or hose connection, one at a time, listening for a change of engine note.
jp 83 Euro S AT 55k