Ok, so my idle with cold engine is almost 100% smooth. Needle barely moves.

Hot is a different story.. Needle moves up and down a little (one needle width each way).

In fact the car just seems to not run as well when up to temp as opposed to cold-ish...

I know the lumpy idle is a long story, but I seem to have it sorted when cold (replaced coil and tightened all vacuum lines)...

Any thoughts? (I do still have a slight leak between manifold and downpipes... Not major)

 

Are all the injectors ticking nicely ? On these cars they all fire together twice per engine revolution, so a dodgy injector need not stop the engine running reasonably well. A "screwdriver stethoscope" should tell you each one is OK or not.

Doug Dwyer may have something to add too.

 

The slightly trembly idle of the Ser III 4.2s has frustrated many owners. Darn few ever achive glass-smooth results, it seems.

Since the ECU commands more fuel when the engine is cold....as well as the idle being higher thanks to the AAV....cold idle is generally better, yes.

Having the injectors professionally cleaned often helps. Don't forget new injectors seals when you reinstall them.

Clean throttle body, all valve adjustments within spec, no vacuum leaks, ignition system 100%, all cylinders even compression....all these things can influence idle quality.

Sometimes a bit of tweaking with the AFM mixture adjustment will improve idle. Unless someone has already been there you'll have to remove the access plug. Make adjustments slowly....it takes a few moments for the system to react to each tiny turn of the screw.


Cheers
DD

 

Thanks for the advice guys. Will tinker this weekend and post back.

 

I am not sure if this applies to electronic ignition distributors, they might be more tolerant of mechanical slop.

In the days of point and condenser distributors, mechanical condition meant a lot.
My friend and I found that lobe configuration was not uniform at all Model A Fords. Some idled and ran better than others. In these and later distributors, I found that shaft wobble meant a lot. My 57 Ford F100 freeway tank had a well worn distributor at one time. If I carefully set point gap properly, it would not start and run!!! However, if I set it a tad loose, the engine would spin a bit and then fire and run quite well. Idle was not good, but passable. A better distributor and this anomolay went away. Issue, sloppy shaft bushings.

My turbo'd Corvair had a similar issue. I found that latter GM sixes had bearings and bushings on the distributor shaft. A bit of mix and match and, I had a much better distributor. the car ran so much better.

Pertronix distributors receive a lot of p[raise and with good reason. But, if a fresh Pertronix replaces a well worn OEM, the car will run better. No question. However, if the OEM were properly freshened, would the oimprovement exist and if so in the same magnitude????

Over the years, I've learned that good ignition is the place to start to get a decent engine. Even some very well worn ones will run quite well with top notch ignition.

But, low compression is hard to make up for, if possible at all.

Carl.