Background: when it was working properly, on cold start it would go to 2000 rpm and when it warmed up it dropped to about 900. After low/barely any use for months (possibly years) it
started not reaching 2000 rpm and when fully warmed up it would stall.
Years ago, but only about 7000 miles ago, I neglected to replace the timing belt and it broke, taking some valves with it. Had a complete cylinder head rebuild job, new timing belt, new water pump. After that job it ran fine for quite a while. The current mileage is about 128K.

Past symptoms: at some point, it seemed like it was running really rich and the mileage was outrageously low, something like 5 mpg, but that symptom is gone. Possibly an injector was stuck open.

Replaced air filter, spark plugs, spark plug wires, distributor and rotor, but that didn't seem to make much of a difference.

Current situation: sometimes it stalls but it mostly goes to very low idle and has some misfiring, sometimes worse than other times. It seems that the worst symptoms have improved lately, not sure why.

The latest tests: with a timing light I noticed that cylinder 2 has very consistent spark, 4, 6, 1 and 3, very few misses, and 5 (longest wire) only has occasional spark per the timing light. Removed that spark plug (it's new and looks just fine), measured the resistance of the plug wire: 8.33 k Ohm, well within what the manual says: 8.5 for cylinder 2 (shortest wire) to 12 for 5 (longest wire). The manual says that the primary coil resistance should be between 0.72 and 0.88 Ohms. I measure 1.11. The secondary coil should be between 10.3 and 13.9 kOhms. I get 13.28.

Could the higher-than-spec resistance of the primary coil be the reason for weak spark all over? I'm tempted to just get a new coil but should this resistance difference be capable of such drastic effects? I've found this supposedly compatible coil:

https://www.rockauto.com/en/moreinfo...t=7060&jsn=116

But the primary coil resistance is 0.98 Ohms, also above what the manual says.

I intend to do a compression test as soon as I get my compression gauge back from someone that can't remember where he put it. But even if that cylinder had no compression, the spark should still be good and it isn't.

Any other suggestions?

Thanks.

 

Check your idle control solenoid. Low idle, stalling and misfures can all be coming g from that.

 

I presume you mean the solenoids of the idle speed controller. Per the manual the 6 prong connector should have the following resistance between various prongs:

2 - 1 and 3: 28-33 Ohm
5 - 6 and 4: 28-33 Ohm

My measurements are as follows:

2 - 1: 38.88 Ohm
2 - 3: 39.23 Ohm
5 - 6: 38.93 Ohm
5 - 4: 39.05 Ohm

A little over spec, but should this cause the problems I'm seeing? Years ago, I had to replace the idle speed controller because the engine would rev up then down then up, etc... One of the coils showed open (infinite resistance). A quick search has shown that the idle speed controller is about $400, so I'd rather not go buy one blindly if it's not needed. If anyone has a source that's reasonable I'd certainly like to hear about it.

Thanks.

 

Have you taken it out to examine it? It can spec OK on resistance, but may have some other issues - gunk buildup, ports clogged, other problems. My idle control solenoid failed in a mysterious way - the ring that holds the plunger came unglued, so the solenoid would randomly stuck closed or open. The computer would have no ability to keep idle correct because of that. The engine ran OK at mid to high RPM, but would nearly die or die on every turn and stop light when engine needed to be just at idle. The CEL code I had for it was Random Misfire...