Car is a 74 djet. When I first start it cold it idles steady at around 1200rpm. After a minute or two it starts to jump back and forth from around 500rpm to 1200rpm or so. Any suggestions on what to look for? CHT? AAR?

i got the same problem; it believe its a vacuum leak. I tried isolating it by spraying starting fluid here and there, but could not find it. My next project is Removal and cleaning of the dizzy.

This is the way the idle gets warm, it jumps around until its warm just like you do when you're cold.......

i would check the AAR and its adjacent hoses, if its a cht issue it may really be an ecu issue and or as well.. the wierdness of it and that it happens in only 1 or 2 minutes usually ARR leak makes high idle, PVC valve issue?? sounds like it is going lean on the mixturte after 2 minutes ect..

below is copied from the ecu doc. link: http://members.rennlist.com/pbanders/idle.htm



My idle is rough and surges when it's warming up
Lean idle mixture during warm-up. According Brad Mayeur, a 914 expert, who worked on these cars in the '70's at a Porsche dealership, poor running during warm-up due to lean mixture was a common problem on the 2.0L engines, not as common on the 1.7L's. The factory "fix" for this problem was to install a spacer between the CHT and the head. The spacer delayed the CHT's response to the changes in head temp, causing the ECU to deliver a richer mixture. I had this problem, and first made my own spacer, then got a very nice replica spacer from Brad, which totally fixed my warm-up issues. Locate Brad using Google if you're interested in getting a spacer.

first of all you must set the idle mix when the engine is hot and after 10 minutes of running. Most people change the idle mix when the car is still in warm up cycle and then never get it right!
After you get a nice idle mix and rpm setting, about 950 rpms, then see what happens the next time you drive it. Yes, it should start up and idle at 1200-1500 rpms at first and usually there is some hunting as the engine warms up which is atleast 5 minutes of driving...
If it still is hunting alot check the hoses to vacuum leaks etc and finally install a CHT spacer to slow down the response of the CHT.