When at a red light, stop sign I get a split second small roughness in motor every 4 to 5 seconds, any ideas.
Thank you

 

Minor faults can be hard to trace and the "could be" list can get rather long. Process of elimination, starting with the obvious candidates and drilling down, is ofetn the only way to find the fault

Could be a slight ignition misfire. Possible component problem (coils, module, etc) or wiring problem (loose connection, fray wires, etc). The later are comparatively easy to look for and correct.

It's sometimes hard to test components as a conclusive fault may not show up until a hard failure occurs.

One easy check is to run the engine in a dark garage and look for sparks "leaking" from the spark plug wires.

Does the problem occur or worsen after a long drive? Coils and modules are often Ok when cold but tend to give trouble as heat builds up. this isn't carved in granite, though.

A clogged and/or otherwise malfunctioning fuel injector can cause an idle roughness. Best bet here is to remove them for professional checking and cleaning. I've done so on many cars (including three Jags) and the idle quality has always been improved.

There are many other checks and others will chime in.

You "gotta start somewhere"....personally I'd go with ignition checks first.

Cheers
DD

 

DD is right regarding the dark garage test; mine suffers the same symptons and in the dark I can see (and hear) the distributor cap arcing and the engine chuffs at the same time.
Doesn't seem to do it under load though.

 

[QUOTE=Doug;716478]Minor faults can be hard to trace and the "could be" list can get rather long. Process of elimination, starting with the obvious candidates and drilling down, is ofetn the only way to find the fault

Could be a slight ignition misfire. Possible component problem (coils, module, etc) or wiring problem (loose connection, fray wires, etc). The later are comparatively easy to look for and correct.

It's sometimes hard to test components as a conclusive fault may not show up until a hard failure occurs.

One easy check is to run the engine in a dark garage and look for sparks "leaking" from the spark plug wires.

Does the problem occur or worsen after a long drive? Coils and modules are often Ok when cold but tend to give trouble as heat builds up. this isn't carved in granite, though.

A clogged and/or otherwise malfunctioning fuel injector can cause an idle roughness. Best bet here is to remove them for professional checking and cleaning. I've done so on many cars (including three Jags) and the idle quality has always been improved.

There are many other checks and others will chime in.

You "gotta start somewhere"....personally I'd go with ignition checks first.

Cheers
DD[/QUOTE
Does it hot or cold, will check in dark garage and go from there. Thank you

 

Yes,I do hear arcing, will look at in dark. Thank you

 

You might be in for an easy fix! A set of plug wires might all that's needed in this case :-)


Cheers
DD

 

Macdoesit, did you ever find the culprit? My car has just developed the same symptoms and I'm thinking it may be the wires but saw this thread and wondered what you found?

Thanks,

Allan

 

Still does it but not near as often. I checked for arcs from plug wires in dark garage saw nothing. Going to run injector cleaner a couple tanks of gas see what happens as it is now rough idle at start up.

 

I just fixed mine. As silly as it sounds, all I did was press down on the plug wires to make sure they were properly seated at both ends. I felt one of the wires move and make a more solid contact, problem solved!!

I'll probably replace the wires anyway as they are getting on in years.

Hope yours gets fixed as easily

 

Not silly at all!

There is a great tendency to overlook basics and assume a problem/repair will be complicated. I've fallen victim of this more than a few times. It actually takes discipline to start with the easy possibilities

Cheers
DD

 

Glad to hear you folks are making progress.

I just wanted to add a +1 to Dougs fuel injector service suggestion. I recently had mine done, not for a lumpy idle, but anyway, the car has never ran better. It also definitely idles smoother than before, although I didn't really think it was lumpy to begin with (Lumpy is my Series III, but thats another story)

My man had a few issues getting the fuel injectors out of the car, and we both suspect this was the first time they had ever been out (after 22 years) so they were well due.

I am now doing to do the same on my Series III and will likely add "fuel injector service" to any future old car "to do" list, such was the improvement I saw in the V12