Everyone has good ideas, so I'll just reply to myself to keep my work all kinda in one place.

I finally got a chance to ring out the harness at the ECU connector. Full results for that check are in the google drive folder. The only 2 things that didn't come out perfect were the throttle position sensor and the engine RPM signal.
- The TPS resistances all came back high (by between 12% and 22%) - maybe within the self-adjustment range of the ECU, but maybe not? Anyone have any wisdom on that?
- engine RPM signal came back with a very low voltage (~50%). May be due to the fact that the engine was cranking, not running? There's no rpm signal loss CEL (no CEL at all, actually), so I'm inclined to say it's just a glitch of my test setup perhaps.

At this point, looks like I need to start really digging down into all the vacuum connections. I sometimes smell fuel when the car has been sitting, so the charcoal canister connections may be wonky. I wouldn't be surprised if the brake booster was leaking too... I'm an electrical weenie by trade, so that's where I went first, but I guess I'll have to get my hands dirty after all!

Responses to others' posts below:

CeeBee1: I removed the hot air pipe long ago because 17-year-old me figured it was the quickest way to clean up the engine bay a bit. AMM reads fine resistance wise, though it's likely original.

Nahtanha: coolant temp sensor was replaced, reads good at the ECU connector

Rico S: all very good ideas! The (mostly) good electrical checks have now pointed me towards an air/vacuum leak somewhere for sure. A good cleaning of ground points is also pretty high on my to-do list.

Dave Stevens - I did toss in a new rotor and wires, but they unfortunately didn't change anything (that would be way too convenient)
--
My Volvo has lasted longer than some of my friendships...

"Just want to reiterate - when the engine has warmed up, it runs well and will restart on the first couple cranks with no bad symptoms. The above only happens on cold starts."

I'm surprised that there has been no mention of a Failed AMM--(Air Mass Meter)---what you refer to as the MAF.

The identical symptoms in my 87---with an earlier version of the LH injection system were cured with an AMM replacement.

Note that I know nothing technical about the 3.1 version or any version later than 1988, which incorporated the diagnostic 'light series box' to get Codes.

All I offer is --- get a hold of another AMM and swap it to see if if cures the problem. Though 3.1 AMM's are not that common.

Good luck

PS: one way(well known) that the AMM dies is that it gets cooked because the Air Box thermostat---sits in that box behind the air filter---fails to shunt the Hot Air from that silver pipe that runs from the Exhaust Manifold to that box---known a the Pre-Heater Hose. If the thermostat fails and the hot air dosen't get shut off after warm-up, the Hot Air toasts the sensor inside the AMM---.


SEE:

Failure of this part is the number one reason for MAF sensor failure on Volvos.

Many gas powered Volvos (and some diesel models) have a simple, thermostatically controlled flapper valve in the air filter box. This thermostat regulates the flow of fresh and pre-heated air in to the intake system. The purpose is to speed up the engine warm-up period in cold weather (primarily for emissions purposes but also for heater function.)

Pre-heated air comes to the air filter box through the aluminum pre-heat hose that is connected between the air filter box and the exhaust manifold or downpipe.

When this thermostat fails, it defaults to the pre-heated air position. This causes super heated air from the exhaust manifold to route through the Air Mass Sensor full-time. Left upchecked, the MAF will soon fail because the electronics overheat. It will also cause the engine to run very inefficiently as the engine management will excessively lean out the fuel mixture in response to the hot air. Engine management systems were never designed to run with ambient air in excess of 400°F.

Check your system on a day when the ambient temperature is above 50°F. The valve should be fully open to fresh air (not pre-heated.) If it is open to the pre-heat side, then you should replace the thermostat. Also, if the valve fails to reach full extension at hot and cold extreme, replace it.

This thermostat is part of an emission control which means we cannot give you advice on defeating this system. Keep in mind that the thermostat is really only designed to route hot air when the ambient air is below 40 degrees so this may not even be relevant in your environment.


https://www.ipdusa.com/products/5451/Air-Box-Filter-Housing-Flap-Valve-Thermostat-for-Volvo-Aftermarket-EL0320-1266826-103083


From the above IPD description: "It will also cause the engine to run very inefficiently as the engine management will excessively lean out the fuel mixture ""

It can no longer react to the ambient Temp---cause it's been toasted---at the MAF. THE MAF will ALWAYS RUN LEAN...even on start up cold...This is likely your problem...as was mine in my 87. The 'hi-tech' computer controlled 'Choke' is 'told' don't bother...it's all warm and good.

In Terms Of OLD SCHOOL carbed engines---it's like starting a Cold Engine without using the Choke ---stumble stall.... as in that Lawn Mower or Snow Blower--at 20 deg F........for the first few mins.

Go back to basics. Got spark and fuel? Both easily determined.

Now, from the archive of bad experiences SOME of the multitude of things it could be:

1/ Internal vacuum leak in the Brake Booster.

2/ Leaking intake manifold gasket (spray around joint with some burny stuff to determine a change in engine speed, therefore a manifold leak).

3/ The stiff, bright, green, shielded OXS signal wire is intermittantly shorting between its inner conductor and its shield.

4/ The case ground of the alternator is hinky. The alternator is isolated by rubber mounts.

5/ Ignition switch is hinky.


6/ The worst case scenario, a field mouse has been gnawing on your 240's wiring.


Richie (near The Burgh)

PS - Let us know how this shakes out. A 240 should fire up after about the third crank (chug, chug, chug) of the stater, then go down the road until it is call upon again. The good news is thse things are maddening, but usually something minor.

Littlefish,

You state the following in your symptoms:

"Symptoms:
Cold starts are generally hard, and result in a lumpy, unstable, high idle (usually up to 1500 RPM). Sometimes the engine will not turn over on the first try. Trying to rev the engine results in sputtering. Audio of representative starting, idling, and revving are available at the google link at the bottom. Spark plugs appear to be fouling consistent with running rich (pics at google link).

Being very gentle on the throttle will make it drivable enough to get going, then it will smooth out and run well after a couple minutes (colder weather = takes longer to smooth out). It seems to me that it gets better when the O2 sensor warms up and the ECU goes into closed loop mode, but I haven't tested to confirm that. Even then, it will sometimes idle above 1k RPM.

Just want to reiterate - when the engine has warmed up, it runs well and will restart on the first couple cranks with no bad symptoms. The above only happens on cold starts."

The statement I'm looking at is this:
"Sometimes the engine will not turn over on the first try"

My question here is this. When you turn the key are you stating that it will not crank, or it will crank, but won't start. If it is that it won't crank, then I would look at your grounds and voltages from your battery to alternator to starter. If you have any type of voltage drop, and in this case it could be significant when cold, that it is not making good contact due to the metals being cold and contracted, and only once things start to warm up that they expand and are now making a better contact, but still not optimum.

I'm only throwing this out there as you have not exhausted all of your possibilities, though you have looked at a lot of things.

Take a look and let us know what you find, if anything. If I've taken you down the wrong rabbit hole, I apologize, but it at least had to be asked.

Regards,

Matt
--
1989 - 245, 1990 - 245, 1991 - 245, and 1993 - 245

Hi,

I can understand the the TLRD statement as I too can write some lengthy posts! I call it a balancing of having some entertainment with a desire to help mixed in with a mystery puzzle play!

I agree with Dave Stevens on the ignition system and most of all a bad rotor button being in the middle of the system but that’s mostly on a no hard to no-start situation.
A bad coil to distributor wire can be a culprit too on cold wet situations.
If it’s running fine otherwise when warm I have a tendency to slide away from that being the total issue.

The plugs look to be just a little bit on the smudgy side, but we know it’s not running right.
The insulator noses are typical for new plugs. The older plugs tell of a little oil burning but no timing issues.
Just make sure they are ALL gapped at .028 thousandths.

The harder start when warm should not be happening, if the fuel rail is getting and holding its proper dose of fuel all the time!
The pressure can drop off overnight but the rail must stay filled up?
It’s the one reason that the pumps run for one second when you first turn the ignition key on.
Try turning it on several times before actually rolling the engine over to see if it helps!

You said you change the FPR so that’s eliminated. That leaves a leaking fuel injector, that is a rare but then there are four of them replaced 20K ago for an unknown reason or conclusion that it was a problem?
Did you do it or some parts changers type mechanics?
That could be an open issue still, if something was getting in them from the pumps and pass the fuel filter?
How old is the filter and the pumps in the car?
What’s the mileage on the cars engine, by the way?
What was the story on changing out the injectors, back, then to begin with?

I would suggest verifying that both pumps are working especially the tank pump. It can cause premature wear on the main pump by causing undue cavitation noise from the rollers on the main pump rotor.
If the wear get bad enough they will not roll smoothly and can develop minute flats spots that can make for pump hesitation to start up. We are talking about an old pump, as it can take a lot of abuse, up too a limit!

Since up are getting hard starting when cold and now hot it’s my prime suspect alone with a check valve on the outlet side that helps hold fuel up in the fuel line up to the engine.
That’s a lot of volume that it can lose and a reason for slow starts cold being worse and now warm as an indicator of something going south, The gasoline.
In the case, south is correct, back to the tank, no matter which way the car is turned! (:-) ???? (:-)

As a side thought, On the variations in idle speed?
With this being a LH 3.1, of which seem to be rare, I would check it very closely with an ohmmeter. It’s like a volume control on a radio that maybe doing the scratching thing, that happens to speakers, but to the ECU.
Look for smooth variations of resistance through it range of motion, especially, right at the first coming off idle.
It must repeat exactly at the idle stop setting.

YOU seem to be knowledgeable in the workings of the car by talking about close loop operations.
For people on this board who are electronically inclined they might tell you to take voltage readings somewhere instead.

Others, like myself, just might consider that the IAC might need a bit of cleaning inspection routine instead! (:). Like the pumps it can also age too!

Entertaining myself again!

Phil

I’d be highly suspicious of the ignition side. Something as simple as a worn distributor cap and rotor and old ignition wires, incl. the coil wire, can cause exactly those symptoms in my experience. These are all wear items and it's generally not worth any diagnosis if these are anywhere near overdue. I’ve also had a badly worn distributor in a rather high mileage 240 giving slightly similar starting problems, but I'd address those other issues first. Wet plugs pretty much eliminates the fuel side. BTW, your thoroughness is appreciated. It not only cuts down on our guesswork here, it also gives us a better idea of your level of experience and the general condition of your vehicle. Please remember to reply back with how you make out so others can benefit, not just for future reference by someone doing a search, but also that’s how we learn from each other here.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now