Erratic idle

[EJP914]

Have '72 1.7 with stock fuel injection. Car starts and idles fine when cold. Tach shows 850-1000rpm when cold. After the engine reaches operating temp it doesn't idle at all. I have to keep my foot on the accelerator at intersections or stop lights to keep the revs up so the engine doesn't die. I've set the idle with the adjustment screw with the engine hot and cold, but either it idles too high or hardly at all. Any suggestions on how to cure. Thanks for all responses.

[John Rogers]

It may be the aux air regulator? Check the hose diagram on the site here and you'll see where it connects. To test it when cold it should let air in so the idle is high and when warm it will close so the regular idle adjustment controls the idle speed. To see if it is working, when the engine is cold, unhook the inlet line and plug it and the idle should drop to 900 RPM or so. If the engine stalls, then the idle is set too low. If you get no change, then it may be leaking. Good luck.

[Dave at Pelican Parts]

Is the head temp sensor plugged in? Is it working correctly?

--DD

[randoid]

Maybe your timing is adjusted incorrectly. I would have that looked at first seeing as it's easier and MUCH less expensive then the Aux Air Reg to fix and diagnose.

--
Randy

[JP Noonan]

My 75 2.0L (same FI as the 1.7L) had a similar problem. Ran great until warm. In my case it was a bad inline resister some PO had put inbetween the CHT sensor and the harness. If you don't have one then I'd agree with DD check that the CHT in working properly. Look at the Tech Article section on this site and the 914 club site, there is a D-Jet testing article that tell you how to test the CHT sensor.