Guy

Mostly a rant here but I am rather frustrated. The 79 has been coming along nicely and I have been trying to log some miles on it to help shake it down. Its been running decent but still has a very slight shake at idle that I have been unable to smooth out. Last Friday, I took it on a short drive. As I started it, I noticed it felt a whole lot better. As I drove, it got better and better. I stopped a few times at a traffic light and the car was absolutely smooth still. I was simply amazed and figured that after 275 miles since its awakening, it must have finally cleared its throat. Drove a few times over the past week and it was perfect every time.

Drove around 25 miles today and all of a sudden.....it started running a little rough at idle. Then started getting a little challenging to start when warm. WTF.

Now, I would be the first to break out the gauges and check pressures again but it was just dialed in 2 months ago and settings are dead on.

Nothing else was changed or worked on. How did it go from slightly rough at idle to NEW car smooth and back again???

Speedtoys

Yo..maybe edit that to a non nuclear-war fontsize?

dr bob

Maybe it's counter-intuitive, but when something is running just perfectly, especially a CIS car, I'd be logging readings for later reference. Then when it starts to act up, at least I have some reference readings to help with the analysis.

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CIS cars and dirt in the system, plugged or deteriorating little bronze strainers, and of course other things besides CIS issues. Start with the usual suspects, like ignition components, and get the system pressures. Look at plugs for variations. Plug In A Big Vacuum Gauge that you can read while driving. Make sure the alternator is charging OK and the battery is holding the charge. Do this easy stuff first, just to eliminate stupid stuff.

Dave928S

What the Doc said ... eliminate all the easy stuff by methodically double checking.

Have you checked the Aux Air Valve and WUR?

Guy

Thanks Dr. Bob, Fuel system is entirely new and clean. Pressures were dead on 75 miles ago but I will be checking again.

My green wire is looks original, anyone think this could be a culprit for the intermittent rough idle? It likely should be replaced anyway so I guess it couldn't hurt

Guy

WUR was rebuilt with a new o-ring and is surgically clean. I did a top end refresh but never checked the AUX air valve mostly because I have a nice cold high idle which drops down nicely once it warms.

I did notice that the idle was hanging for a second prior to coming back down. Can't find a vac leak, everything is new

Guy

Had a little time today so I hooked up the CIS gauge and did a full set of readings from start to finish. Everything was exactly the same as it was two months ago. I seriously expected that I was experiencing the symptoms of high warm pressure but it was 42 without vacuum.

The only change was a very, very slight shake of the needle when reading system pressure. It used to be dead steady. I have a new accumulator installed. Again , it was very minor.

Car was still rough at idle. Running like it had a misfire.

I then changed out the plug wires. No noticeable improvement although the old coil wire had a loose fit at the coil.

Then, with no warning. The car smoothed out again. Not quite at its best performance, but worlds better than yesterday. Took it for a ride and it did very well. I am not sure whats going on but I am going to continue to log miles. It may be related to the amount of use it got yesterday, lots of stop and go traffic with lots of little trips throughout the day. Maybe I Can reproduce the condiitons.

The good news is that this car ran perfect last week, as steady and smooth as my 997 which means whatever these issues are will be solved and it will be like that once again!

The Forgotten On

If you think your green wire looks original, replace it.

If it is a dark olive green or not even green any more, replace it as it should be a bright florescent green if it is new. They can cause all sorts of weird running issues.

linderpat

I also vote for a failing green wire as the culprit. Especially based on everything else you've done.

dr bob

There's a lot to be said for some good old-fashioned ignition diagnostics. I have a used-to-be state-of-the-art tektronix oscilloscope that gets dragged out once in a blue moon for a session with a car that has less-than-obvious problems. These days you can find USB plug-ins and software for this kind of stuff, and run it on a laptop or tablet. There's a slew of info available from a couple wires wrapped around the coil wire and #1 plug wire. Uneven firing voltages, shorted, open or leaky plug wires, dirty or mis-gapped plugs, all that in the spiky lines on the scope display. OBD does a lot of interpreting for you if you have a "modern" car to plug into. Absent that, sometimes the old tools and methods are still appropriate for the older cars.

Guy

I haven't used an oscilloscope in 25 years but your point is well made. Going back to basics so as not to overlook the obvious.

I find myself a little too "fuel" focused on these CIS cars

Guy

Ordering one now. It needs to be done regardless. My wire is olive and the connector looks like ancient history

Thanks!

AirtekHVAC

Hey guy, sorry if I missed it, did you rebuild your fuel distributor? That fixed my rough running problem. My "olive" wire is on the list....

Please let us know how it comes out.

Thanks.

vze2jshn

Pour a bottle of Techron in and see what happens.

Guy

Thanks, I have been running Techron over the past 250 miles.

Yes, I had Rebuilt Systems (on eBay) do it back in November. It was baddddd...... best 150 dollars I ever spent!