i did not read every word written on the problem.

did you check fuel pressure? can you check it while driving? sounds like the fuel pump is tired or wrong. every problem i've seen like you describe sounds like low fuel pressure and volume. even new pumps that are sold for these cars but are not bosch do this. so, no airtex, carter, walbro-nothing but bosch if you have to replace it. and yes, you could very well have a tired bosch pump. this ASSUMES the feed pump is working correctly. the main pump has no guts if it has to pull from the tank and push to the engine. verify tank pump volume and fuel pressure at the engine. good luck, chuck.

im listening intently to all these good suggestions.
I spent the weekend actually working on my 740 not the 240 just because I thought maybe I can fix it's issues up faster and then tend to the 240 with the problem of it failing to acellerate..

the 240 runs smooth as silk when it runs properly so some gremlin crept in , es I can try a different FPR or AMM. maybe the capacitors start to fail in the ECU I tried to recap the one in my 88 Van, almost the same thign really it had 3 or 4 little electrolytic caps. I failed because I clipped a transistor in a slip up so I set it aside and bought a rebuilt one.. I could try to recap one of the volvo ones.

withthe 740 its runnign funny but in a slightly different way, same engine but a year or two newer so it doesn't' have any memory, the check engine light is on and I keep wondering why. the older 240's had a thing on the back of the speedo that I'd reset, so the warning was just a reminder to change the timing belt but I could find no such switch on the back of my 740 speedo.

I thouhgt I might go back to square one and try to adjust the timing on the 240, and check the throttle switch. I noticed that when working on the starter issues that I had recently that if I left the ignition on and reached in there the idle air control valve was sort of vibrating. I pulled another and stuck it in there, changed the little vacuum line for the manifold down to the screen above the flame trap and the one from the FPR to throttle body, not much difference. I sprayed most of a can of throttle body cleaner and sea foam in past the AMM hoing it would perhaps claar some gunk if it was dirty in the throttle body area.
It runs pretty well on power, but idles and shakes in a weird way. I wondered if maybe the balancer shaft slipped or is mis-timed, maybe I should do the belts or at least pull the timing cover and check the marks are right. it doesnt vibrate that bad once it's going down the road under power.

the 240 is 1990 and has a TDC sensor, Ive had issues with that. in the 740 it has the hall sensor int he distributor and it's had issues too causing a no start, obviously both are working now as they do run.

in my ford van, the way the timing is set , there is what ford calls a "spud connector" its a little jumper you can unplug and it disables how the timing is over-ridden by the ICU which then allows you to adjust the timing with a light and turning the distributor. ,Then you plug it back in. Volvo doesnt' do it quite that way but I'd like to make sure the timing is right. if my timing isn't set right maybe that could make it shake like this?

im not finding any leaks, but I could look further. yes Ive seen how any leak especially between the intake and mass meter can make it run really bad.

new motor mounts might not be a bad idea. I've seen cars where I could take a 2x4 and sort of pry up upon the engine to see them broken. Ill check compression to see if any cylinders might have weak compression. maybe I should buy a new mass meter. I noticed that rock auto, at least for a while had just the element so it can evidently be changed,maybe cheaper?

It was all I could do to get the 740 on the road, the signal lights had an issue but it was just a bad bulb socket. I put all the dash back together. although it's shaky at idle , it runs better than the 240 with the stalling out issues.

I still have basically two issues, the 740 runs strong but shakes at idle, its not quite right. the 240 runs but goes very weak on power intermittently.

I think the issues are quite similar in that they seem to relate to them just not running smoothly. both seem to have engine lights on but neither is letting me extract any codes. the 88 740 wagon has no code reader and the 1990 240 doesn't return any blinking.

do the engine check engine lights mean that it has a code stored? or is this something to do with the timing belt and just need resetting? they aren't overheating.

although not related , my 88 ford van also has similar issues, it is missing and running very rough , but running.

I'm ok changing any part but diagnosing these issues seems to be making my hair fall out..

I have a spare 740 standing by, it has a busted windshield and I have a spare windshield but haven't driven it. but Ive been trying to leave it alone and keep it intact, if I need to pull a part for testing I can. its a 1990 and has the code reader.

I have a spare line from the fuel rail to the filter and pump and a spare fuel rail, I was thinking of using those fittings and just connecting it to a pressure gauge so I could install a gauge temporarily where the fuel is fed into the fuel rail. If I can rig that up maybe i can at least make comparisons from one vehicle to another.
can I just use a gauge for air or water pressure? maybe if I can quantify what the fuel pressure actually is it could be a clue or at least prove its not the FPR ? likewise I do have an old vacuum gauge so maybe there are some ways to measure what the manifold vacuum should be, and see if its ok.

I tried spraying carb cleaners and things around the manifold gaskets and couldn't detect any vacuum leak that way. I'm thinking that making a smoke tester to feed smoke in might help decide if I have a leak anywhere that's gone un-nnoticed.

thanks for the great help with this, I'll keep thinking and trying to figure out the basis of all these issues. I'm having quite a time isolating any of them.
sometimes it's a matter of using a process of elimination and used parts going to a drive after swapping out this part or that.. I might hit upon the right thing that way..
just looking for something that make enough of a difference to feel like I'm on to something substantial is a help. right now I'm just confused.

I figured that I found the rough running issue because I did find an injector that wasn't injecting. last year the 240 had one that was stuck on and flooding a cylinder.. but i got through that and it ran fine since. It blew a head gasket and I fixed that. its been ok over winter. for some weird reason the 240 can run smooth has silk on idle once all is working right, but the 740 seems to shake a lot more at idle and has done for a while.

It seems that although that was an issue and I fixed it, it still shakes a lot.. i do have an oscilloscope maybe I could try looking the trace to the coil, or before the powerstage, or to the injectors and see if the profile looks right. maybe I'd see differences in the oscilloscope trace from one car to the next. The cars are all obviously seeing a pulse because they run but maybe something gets goofed up due to bad capacitors in the ECU.. I can swap around ECU"s or ignition modules, not usually the first place I'd start. If I could switch ECU's and see some improvement it might mean something..

Ive primarily run all my cars on higher octane fuel , thinking it may avoid such issues.. I dont really know if that makes a difference but Ive heard it is better for when a car is parked. I haven't noticed any fuel starvation issues like weak acceleration when they get going, any of my cars seem to run ok if it's at full throttle but I think that just masks a lot of more subtle issues like vacuum leaks or timing slightly off, or idle control valve issues.

I thin I have a lot to check but maybe sould first verify if the timing is correct and that the throttle body switch is working correctly. maybe I can probe the idle air valve and see it reacting by way of the throttle body switch being open slightly or closed. i noted it has 3 pins and wondered what the third is for. is it on or off or would it have mid positions? maybe I can blow through it and apply power to check it. or similar. I think some volvo ones have three hoses, these ones just have 2 hose connections. I think my Porsche 944 has the same bosche valve. I sprayed brake parts cleaner and then some some throttle body cleaner in it yesterday, switched it out for another one in the process, I did not see any big changes.

Hi,
I recently had the same problem on my 90 240, although the stumble went away with a fully warmed up engine.

After swapping a known good ECU and AMM and checking fuel pressure without effect
, I went on a fairly long drive and noticed my gas mileage was down.

That led me to think that a small leak at the header pipe to cat connection that I had been negligent to fix might be at play, and indeed replacing the gasket cured the fault and improved the mileage.

My guess is that the O2 sensor was sensing a high oxygen situation and the 951 ECU was sending more gas to compensate. On a cold engine this might have caused a momentary flooding and stumble on acceleration.

I recommend that you check for any leaks in the exhaust between the engine and O2 sensor.

Good luck, Peter

A couple of things that are simple and cheap.

Air filter - I once had a Mini in the 60s that was not running well so I had it tuned by a specialist - on the way home, it died on the highwy. My uncle sent over a real mechanic - he removed the air filter and it ran fine!

Try removing the air filter for a short ride

Mass air plug - once our ’88 745 would not accelerate - I tried it several times on my street - for some reason, I backed up - It ran like a jack rabbit in reverse. I checked the plug on the air sensor, and found that one pin had been pushed back, when I fixed it, it ran fine.

Check th pins on the sensor - this is one plug that is disconnected and reconnected during service. I pulled the boot on the plug and made a line across the wires so I could see if a pin was pushed back.

When I had issues with a 740 that was idle when I tried to sell it - my service writer gave me a small tube of dielectric grease and told me to unplug connections in the engine compartment, clean the connection, apply dielectric grease and zip tie any plugs that I could - this fixed the issues - I did one each week so that if I had a problem, I knew which plug it was.

Good luck, you have plenty of things to try!

In addition to the other Phil's good ideas and suggestions, especially the FPR, my first thought on reading your description was a faulty AMM. I would definitely want to swap in a known good one to see if the acceleration improves when blipping the throttle. In one of my LH 2.4 B230s I suspected the AMM was getting a bit unresponsive when pressing the gas pedal. I swapped in the one from my B230FT and the engine ran as normal. Figuring I had nothing to lose I took some supposedly decent spray AMM cleaner to it and managed to make it worse. I then decided to treat myself to a nice rebuild from Injection Labs, with the original now on the shelf as a known poor spare.

I've never heard that cleaning makes much of a difference with our hot wire AMMs. If the AMM burn off cycle starts to become less efficient then the platinum wires may start to accumulate dirt, especially during long trips. To help prevent your AMM from overheating and having a sudden failure when the air box thermostat wax piston decides to give up, the general recommendation has always been to permanently disconnect the pre-heat hose off the exhaust heat shield unless you live in an Arctic climate. You don't have to worry about BC AirCare anymore, but in the old days I used to screw the air diverter flap shut inside the air box, out of sight of the inspectors.

Unmetered air or inadequate vacuum momentarily getting in the way during acceleration could be split/loose hoses. Inspect carefully the vacuum line rubber collars on top of the throttle body for signs of splits as well as all other vacuum fittings and vacuum check valves, such as on the brake booster. Also carefully check the accordion air intake tube for splits starting in the bellows (usually out of sight underneath). Under acceleration, in addition to the vacuum changing, another thing that changes is engine torque twisting the engine on its mounts, which can momentarily open a hose split wider, especially if an engine mount has gone soft or a face of the mount has separated.

--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi,

The most likely cause is supposed to be the fuel pressure regulator as it is made to stop returning excess fuel to the tank under accelerations.
A vacuum and its port from the intake manifold is the trigger mechanism for it to work.
You might have a plugged up port source. Easy enough to check out before getting all warm and fuzzy with pressure gauges. 🤭

If it’s not starting hard from the lack of rest pressure inside the fuel rail or acting like its flooding, then the FPR is most likely OK.

The next thing could be a CPS starting to go wonky as it affects the timing but then your idea of a bad throttle switch that tells the ECU what you are wanting to do next is a good start in the proper direction.
The TPS has to show a change of state each time it moves. Idling to off idle and to wide open throttle.
The END between zone is left to the FPR’s calibration.

The vacuum at idle works in conjunction against a preset spring pressure and the incoming fuel pressure to open the valve seat upon starting. Otherwise it should stay shut.
At idle it is there to return some fuel to the tank.

When less vacuum occurs, then the valve, that was partially open, is adjusted to completely shut down and the fuel backs up on the rail side.
Then the injectors have more fuel volume to spray with.

The ECU controls the time open and is known as “pulse width.”
Its uses the O2 sensor signal to adjust mixtures and a RPM signal to set the timing advance sooner to get the burning going sooner as RPM increases.

The ignition systems only work so fast to get sparks there soon enough!
The spark from an ignition coil is only “X” long in duration too.
So, from some beginning point, the rest of the added fuel is supposed to all burn up. 🤫
But we know that never truly happens or we wouldn’t need catalytic converters. 🤔
Yes you get more power only because you cram in more cycles per second and forget about those left overs doing any more than they could do before!
You can smell a mismanaged engine on any grade right away but unless you are behind your own car you’ll never know. Isn’t that beautiful about combustion engines even at 35,000 feet.🙄
I hope they are more sophisticated up there than down here!

Have you got the spark plugs clean and gapped correctly? As that can be somewhat critical on the red blocks believe it or not.

Yep you will have to think through what you feel and can find to iron the wrinkles out of this one, especially if it’s intermittent.
😬

Keep us entertained!

Phil