looks like fuel pump and regulator is working, injectors not leaking, pretty normal for it to drop a little. I would suspect something to do in the air intake and regulation. unplug fans and see if noise goes away. so long as you dont leave them unplugged for very long you ok.

 

I agree, it seems like the fuel components is falling of the list of prime suspects, will test one last thing though, disconnect the vacuum hose to the regulator while surging, just to see if the higher pressure will make any difference.
And will have a look at the fans next time the air intake stuff is off, disconnect them will tell if they making the noise or not.

 

As expected, disconnecting the vacuum hose to the regulator while surging made no difference.

I did a smoke test last night trying to detect any vacuum leaks.
Disconnected the brake booster and hooked up a piece of garden hose to the intake.Had bought a fat cigar the day earlier, engine off but warm so any gaps triggered by heat would be there, started puffing on it and blew in smoke through the hose, used half of the cigar.
Then looked around all over the engine bay with a light to see if any smoke would show up, used a mirror for the backside where the EGR is, but no smoke to be seen anywhere.

Before reconnecting the brake booster hose, I blocked the intake connection and started the engine, just to be able to exclude any possible internal vacuum leaks in the brake booster.

I haven’t smoked since the previous century, maybe this car will drive me to drinking too LOL, seriously I need to get this fixed, ended up in a traffic jam yesterday which was no fun when the surging kicks in, like sitting on an untamed horse.

One thing I did notice yesterday during the surging on the driveway was vibrations, not much but a little.

I finally got my Foxwell 301 yesterday, so next troubleshooting session I hope to be able to capture some live data using that, to be continued …

 

Have been scanning live data for two times now, but I likely will be needing to do again and in between to study how to catch things in there.

But so far the result is:

Codes check ok

IM readiness test ok

ETC 106-108*c (222-226*F), seems a bit at the higher end, but I don't know what it should be

Short time fuel trim stayed in between the -5 +5 area which from what I understood should be normal and should had typically been higher if any vacuum leaks

Long time fuel trim was mainly a 0 from what I could see

O2 sensors stayed below 1.0V, but when I ran a graph on one of them I did notice that the sinus curve tended to stretch in the surging phases

Also something called Sparkad V (timing advance?) fluctuated at surging, was 15 at idle but raised to I believe 25-30 at surging, could this be a indicator of bad ICM or opti?

 

Have been looking on some recordings and need to correct the above, both short & long time fuel trim had negative digits on both banks, values in the 0 to -3.9 range.

Also noticed the MAF moving 7 to 16 while the surging

 

The hot day we had here put the car in its most surgy mode, which was perfect for troubleshooting as the problem can be intermittent.

Started with a drive to warm up in which I monitored the Short time fuel trimas a graph on the OBD, and got up nice numbers this time, all within the -5 to +5 area.

When I got back on the driveway, I blocked off the vacuum connections cluster by cluster, first all four on the passenger side (HVAC, Fuel reg, hose to the valve cover and EVAP), then the four on the drivers side (PVC-line, EGR, Opti vent and brake booster), started up the engine in between to see if the surge was still there, which it was.

Though I had found something for a while with a real spongey rubber 90* connection to the PVC valve that I replaced with 10mm hose, and the surge was suddenly gone, but after a drive it was back again sigh...

Before ending today’s session, I sprayed carb clean around the injectors in case of vacuum leaks there, I’ve done this before but thought I’d do it again to definitely close the vacuum leak track as a reason for the surge.
I also measured the temp on the outside of the water pump with a thermometer, which showed 90* C (194*F), OBD says 106*C (222*F) which is what the sensor measures the coolant to be, and I guess the difference is reasonable

Think I’m soon ready to order a new ICM and coil now, was thinking Delphi

Below update
Parts being replaced so far:
IAC
TPS (but have put the old one back, as the new cheapo was crap)
Both temp sensor (due to dead gauge)
Throttle body gasket
Elbow
Fuel filter

Stuff that has been made:
MAF been cleaned with MAF spray cleaner (and unhooked while surge)
ICM mod (washers installed to separate the ICM from the head to spare it from heat)
EGR has been off, checked the diaphragm with a vacuum pump, cleaned the valve section with some brake cleaner, and also cleaned and lubed the diaphragm shaft
TB cleaned and re-torq with new gasket
Intake manifold bolts, studs and throttle body bolts all re-torqued
Pulled the vacuum hose off the EGR while surging to see what happens
Sprayed carb clean around the injectors to check for vacuum leaks
Recalibrated the IAC
All intake vacuum connections ( four on each side plus one on the front) has been blocked off to see if it had any impact on the surge, which it hadn’t
PVC valve checked (not stuck)
Gas cap off
TPS shows 0 in the live data, which I believe removes that as a suspect to cause the surge
Fuel pressure checked, 38 psi if just cranking and 32-34 psi engine running

Stuff that I have been thinking about to do next:
Run a OBD graph on the O2’s
Measure the vacuum in the intake while surging
Check for exhaust leaks around the O2’s
Somehow probe the IAC so I can measure voltage alternation while surging
Replace ICM and coil

 

have you changed pcv valve?

 

I had it out for a check, and it rattles fine so it ain’t stuck,
Plus I had the pipe connected to it as well as the PVC itself blocked off, and the surge was unaffected

BUT it strikes me now that you ask, that the hose at the other end of the pipe connected under the TB have just been visually inspected (while servicing the TB), so need to spray carb cleaner around that too to have covered all vacuum leak bases.

I add a pict on the block offs at the TB just to show how i did them

 

so you have access to a vacuum gauge? maybe try to see what vacuum is doing when idle goes up.

 

Interesting thought, I could hook it up on the Opti vent connection that is plugged anyway right now

I don’t have one, did lend one earlier when I checked the Opti tightness, but I could buy one

Thanks for the hint Craby!