79 - Low Idle
 

Symptom: So for about a week at cold start my beloved shark would tach at 3k then drop down to 2k after normal warmup which is 1k higher than normal. Now at cold start she does not reach 1k and idles at roughly 300-400. Any suggestions where to start? :(

Maybe start with the AAV test.

<iframe width="853" height="480" src="https://www.youtube.com/embed/FO6BFmDrdSE" frameborder="0" allowfullscreen></iframe>

Please tell me the music will play when performing this test !!!

My US 82 Auto show that rpm but idles like a Cadillac. A little rough on take-off but very livable.

Tino

Warm-Up Regulator
 

Hey Gryphon - Another possible reason for your idle issue may be the WUR (Warm-Up Regulator). It is responsible for setting your fuel pressure at the air/fuel control arm in the fuel control unit while the engine passes through a cold start to a warm engine.

One other comment - To perform the pressure tests needed to diagnose most CIS injection problems you must (buy or borrow) have the proper adapters, test gauge, shut-off valve and fuel line setup. J.C. Whitney used to carry a nice very reasonably priced unit. They are well worth the purchase if you intend to maintain an early Bosch CIS car.

Here is one of the many discussions on the WUR - although normally factory set, they can be adjusted to tweak the final pressure setting. The Bosch CIS components and operating principle is the same no matter being installed on a Saab, BMW, Mercedes, Porsche, etc....

Pelican Technical Article: 911 Warm-Up Regulator Adjustability

Keep Us Posted on your progress, Michael

CIS Pressure Gauge Set Up -
 

Here are a couple of photos of the CIS Gauge - and a couple of the tests being plumbed up. If the +12 volts supplied to the interior heater element is missing on your car the resulting fuel pressure regulation will not be correct and can produce all kinds of idle and run symptoms.

About half way down the page is a photo of the gauge set up -

FUEL INJECTION TESTER FOR CIS-K-JETRONIC BOSCH SYSTEMS - Page 2 - Rennlist Discussion Forums

This is a description of the WUR test procedure -

Pelican Technical Article: Testing Bosch CIS


Here is a Utube procedure for running a CIS pressure ops check -

https://www.youtube.com/watch?v=h7drhxjJ2mg

Michael