My car went from running good to not idling. Suddenly, no warning. I used my 72 Valiant for multiple errands today w/o incident. Then on the last one I put it in gear and it stalled. It started right back up, but won't idle. I have to keep my foot on the gas to keep it running. Where should I start to diagnose my problem?

Vacuum leaks would be where I'd start.

Use the idle screw to bump the idle up to where it will keep running. If it's too high, then you'll need to get a helper to avoid hurting things.

Valve lash, if appropriate. Check you valves.

When did you last change the fuel filter?

Oil level OK?

CJ

_________________
Part of Tyrde-Browne Racing

I will look for a vacuum leak.
The valve lash was set a couple thousand miles ago. How often should it be checked?
How would the oil level affect idle?

A quick indicator on valve lash:

If you hear the tell-tale putt of a miss at the tailpipe you have a tight valve. If your loosening up in a couple thousand miles, you are:

A. Driving like me, really hard, or

B. Experiencing valve recession.

There are other factors that play into frequent valve adjustments, but that covers the bulk of poor idle quality issues.

Oil level: Low oil level will result in higher temperatures, more contaminants entrained in the oil remaining, and excessive wear and friction. This isn't a sudden onset like you experienced, but it's worth exploring.

Another consideration; Check your timing, and verify you aren't seeing a lot of variation in base timing. If it's bouncing around a lot, you may have a spring perch that needs adjusted in the distributor, or your vacuum advance may not be functioning correctly.
As vacuum drops out from the ported vacuum connected to the vacuum advance pod, it may be backing off advance between neutral and drive. There should be enough advance to idle with the vacuum pod disconnected.

How old is your timing set? Virtually all timing chains and gears are shot at 100k miles. This is not a sudden onset, unless the vehicle has been sitting for many years, then taken out and driven. A tight, very old, and rusty chain will very rapidly wear to an unusable state. Likely not what your issue is, but something that bears mentioning. It can, over the course of a long series of drives, result in the cam retarding.

Most likely, running errands with repeated heat cycling, your stack gasket (Manifold) has developed a vacuum leak.
Don't forget to check for damage and leakage of all vacuum lines. If they are old, replace them.

CJ

_________________
Part of Tyrde-Browne Racing

Could be as simple as some trash in your needle valve.Clean it and see.I just had this happen to my 63 Valiant. HyperValiant

_________________
1960 Hyper-Pac Valiant(rolling test-bed)
1963 Valiant V2OO(Son's summer project,- he just turned 15 )
1972 Valiant 4dr(Daughter Kelly's repair in progress)
1974 Valiant (v8) daughter Kelly's work in progress

Or you could have sucked some dirt into the idle circuit. First thing I'd try if you don't see any obvious vac hose-leaks is what I call a "vacuum surge". The idea is to raise the engine speed up then "seal" the top of the carb briefly to create a STRONG vacuum to try a suck any junk through the carb circuits.

So there are two ways to go about this- the "he-man" approach is to remove the air filter & its bail clip- then use your hand to seal the airhorn. The second method involves pushing the choke flap shut (less sealing, but more safety). Either way you start the engine - set the idle screw high or have a helper goose the throttle to keep it running. Then in one motion you force the throttle wide open while sealing the airhorn (hand or choke blade). Ideally you uncap the carb JUST before it stall & raise the rpm's to clear the RICH-rough run (there'll be lots of black stink out the tailpipe). If it stalls hold the gas to the floor & crank until it restarts - it'll run rough until it clears the excess gas out. Repeat if needed. Sometimes that helps.

_________________
63 Valiant Wagon
225 - 4 bbl

Thanks! I will check on all these things, but I drive conservatively. The engine is VERY worn. Piece by piece getting a new one together. Just hoping to keep running and driving until then...then on to the transmission

Vacuum leak wins!

You have a PM about the intake.

Rick

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Check your PCV valve, if it is stuck open, it will produce a vacuum leak at idle. Simple to test: remove the hose from the PCV valve - or the PCV valve form the valve cover - and plug it. If the motor then idles normally, the PCV valve is bad, and must be replaced.

Olaf

_________________
Aspenized