The Search for the Source of an Idle Surge, Pt. I

"Urambo Tauro" (urambotauro) 03/18/2016 at 19:00 • Filed to: wrenching, beater build, blog, murlequin

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Now that the !!!error: Indecipherable SUB-paragraph formatting!!! has all the critical stuff taken care of, its time to focus on some of the less pressing, but still important items. This was kind of a lengthy adventure, so I’m breaking the tale into two posts.

The original craigslist ad disclosed a “surge at idle” that I shrugged off, certain that it was within my abilities to solve AFTER I took care of the other stuff. The issue: when sitting in gear at a red light for more than a few seconds, the idle would start to fluctuate between 500 and 900 RPM, and after bouncing around for a few more seconds, it would sometimes stall completely.

Because it would happen consistently, I anticipated having to restart the engine by shifting into neutral when stopping. To my surprise, taking it out of gear prevented the surge from occurring at all. When the light turned green, I could put it back in drive and go, without holding up traffic.

The previous owner had been trying to fix it himself, but had not successfully found it yet. Cleaning the IAC didn’t solve it, nor did replacing the ECT sensor. The next shot-in-the-dark on his list was to try replacing the distributor.

Now I didn’t want to go around replacing parts without confirming the need to do so. So, I searched around on forums and such for help. Unfortunately, there were many possibilities that all seemed equally likely. Could be a vacuum leak, a timing issue, an EGR or IAC problem, electrical fault, etc... And no orderly flowchart of what to check first.

So I just started picking away at it. I checked the grounds, sprayed around for vacuum leaks, pulled out my meter to check the coils and other components... My attention was soon drawn to the distributor shaft, which had some play in it. It appeared to be the original distributor, so maybe the previous owner was on to something...

So I picked up a new one and decided to throw new plugs and wires on it while I was at it. I marked the old rotor and distributor positions, and pulled it out with the plug wires hanging off like dreadlocks. I stabbed the new dizzy in place, exactly the same way as the old one, then gapped and installed the new spark plugs. As I started to install the new plug wires, I realized that the old wires did not match the diagram.

This threw me for a loop!

Everything was one post away from where it belonged. I went back and forth several times, re-checking my new distributor, re-checking the old one, re-checking the firing order...

I determined that the old distributor had been installed incorrectly during the previous rebuild, and that the housing was clocked to make up for it. Techinically, this did not affect engine operation, so all I really had to do in order to get it running again was wire it up the way I found it.

Yeah... NO. I’m putting this back the way it belongs.

So I turned the engine over by hand until I had cylinder #1 @ TDC and re-stabbed the dizzy, turning the rotor so that it would point to the #1 stud on the cap. I then wired it all up- by the book this time.

I pulled the advance connector, hooked up my timing light, and timed it to 0° dead-on. After reconnecting the advance, it was time for a test drive!

Alas, that didn’t fix it. It would still surge and stall as before. In fact, not only was there no noticeable improvement, it kinda felt like it was actually slightly worse, and more prone to trouble...

Because I decided to set about replacing the distributor before I ever got around to checking the timing, I’ll never know for sure... But I have a hunch that whoever worked on it before may have advanced the timing. This might have been an attempt to fix, or perhaps cover up the problem, but it’s also possible that someone had simply set the timing by ear, without using a light. Come to think of it, when I pulled the timing advance connector, it appeared to be undisturbed within its bundle of wires, as if I was the first to open it and time it this way.

But no matter. All that effort turned out to be preventative maintenance rather than an actual repair. To be continued in !!!error: Indecipherable SUB-paragraph formatting!!! ...