Rough Idle/Dies When Cold

[Steve L]

I have a 74 1.8. When cold the idle is very rough and occasionally dies. At revs above idle it runs fine and when warm it even idles fine. I have done all the ignition checks/replacements and all new vacuum hoses and seals. I think it's either the cold start valve or the auxilary air regulator. Any assistance is determining which part to order (if any) would be greatly appreciated. Thanks in advance.

Steve Lawrence

[John Rogers]

Might be the Aux Air Reg. It is easy to remove and when cold air should pass right through. You can see the valve open. ook up a 12v dc power to the pigtail and ground to the body and it should get warm and open is a few minutes. Ours was stuck shut when we got our 1974 and it caused a very low idle when cold. I soaked it in WD40 for a couple of days and it is fine now.

[Dave at Pelican Parts]

There are a number of test in the Haynes manual chapter on the fuel system. They are a bit scattered through the chapter, but dig through and find them. They can help you test the various components.

This assumes the stock 1.8 L-jet FI, of course.

Easy tests for the AAR: Air should flow through it when the engine is cold, and none should flow when the engine is hot. Pull off one hose and try to blow through it. (Engine off, as removing the hose makes for a BIG air leak and the engine will generally run REALLY crappy or die.)

The cold start valve only works when the starter is engaged, so it almost certainly isn't the problem. (Unless it is constantly spraying or leaking.)

The other main temperature-dependant part of the system (other than the engine itself) is the head temp sensor. That lives down by the #3 spark plug in the head. Haynes has a picture. Check the resistance from the plug to ground. Should be ~1500 ohms when cold, ~100 when hot, as per Haynes.

Good luck!

--DD