I have an intermittent miss. Can't put my finger on it
This is old stuff but I am going through the process of elimination.
1) just put all new plugs
2) wire set is 5k old
3) injectors were just cleaned by Witchdoctor in Washington
4) Vacum hoses either replaced or inspected
5) fuel lines are all new from the tank forward
6) Fuel pump is about 10,000 old
Yes I only use Chevron and I have never put diesel in it.

At speed it doesn't miss, only low end city driving and it will pop back at times when sitting at stop light

Here is the scary part...I replaced the big belt about 5m ago
Inspecting it, my guess is that it's a bit loose. There is about an inch movement when cold. Its a Gates belt with a Porkentensioner. Could it have jumped a tooth?
The timing is right on the center mark.

 

what are the cam marks at when the balancer is at its mark.

 

after checking the timing ,
remove the intake tubes and run the engine in the dark,
look for jumping sparks from the wires,
and if the green wire is old replace it

 

Perfect advice...was thinking green wire also

 

I will give this a try tonight
Also I have a small vacuum leak behind the HVAC. I'm going to chase it tomorrow
v

 

In the dark
No sparks and no miss. Idles perfectly, when rev'd and held at 3m it doesn't miss a beat. Only under load when going through gears does it miss. Could this be a vacuum leak somewhere? Does vacuum need to build up? Is it that little hissing in the dash that is my leak and causing this?
When I pulled the plugs, all were running lean, maybe a bit too lean? All a bit toasty.

 

Usually the HVAC actuator leaks are not terribly significant in terms of the engine vacuum as they are at the end of long, small bore tubes. But I've never heard one hissing. It would be worth checking engine vacuum and seeing if the leak is significant.

 

Cam timing aside this sounds too loose-- depending on how hard you had to push, to get that inch of movement. The belt has 5000 miles but what about the tensioner? Was it new then also? If the tensioner is older, what was done when the belt was changed?

It could be an ignition miss, but your wires are pretty new. And toasty plugs would be more consistent with a lean mixture.

So tell us about the MAF... Has it ever been rebuilt? How many miles ago? How many miles on the car?

 

I put a new Porkentensioner in along with water pump when I did the belt 5k ago
The ODO says 112k and I think it's accurate. I have owned it a little over 3 years and I drive it about 10k per year. Mostly hwy ( Bay Area to LA) I have never messed with the MAF
Long hwy trips it runs great. In town is the problem

 

no MAF on an 80 928,
But it does have the famous green wire

 

I'll replace the green wire just to get that out of the way
Why are they so expensive?

 

Given the symptoms, especially "Only under load when going through gears does it miss.", my first thought is a minor fault in the secondary ignition.

The ignition system develops enough voltage to get to ground (earth). Under normal conditions, this means enough to jump the plug gap. The voltage required to jump the gap varies with throttle opening. This is because air is an insulator, and more insulation gets packed in the gap at larger throttle openings.

More insulation in the plug gap means that higher voltage is required to jump the gap (fire the plug). If the ignition system can develop this higher voltage, and if there is not a voltage leak at the higher voltage level, all is well. It is not all that unusual for a high-resistance connection or break in the secondary ignition system, or a fault in the insulation in the secondary system (including inside the coil windings), to cause a misfire at larger throttle openings.

 

^^^^^ Given that, how's the distributor cap and rotor? Any cracks or carbon buildup detectable inside the cap?

 

Absolutely, this is a good place to look, and WallyP's analysis tells you why. Back in the 70's CB750's would roll into my shop with those symptoms, all it took was a look at the inners of the spark plug caps to find the carbon traces that caused it. Easy. Not so easy was my XJ40, where it took time to find an almost microscopic hole in the nose of a coil that was causing the problem. Not always easy. One thing you can try is WD40'ing everything on the high tension side as a start- if the symptoms disappear, this is your problem.

 

Green wire all the way.....however its easy to look at cap-rotors to see if they are worn..... If you haven't changed the green wire its safe to say its original....which can lead to all kinds of bizarre issues