Lurching at idle

crawlvo

ah - another 'Rough Idle'.....

But, recently I've noticed when coming to a complete stop (braking) the car will lurch around and rev in this weird bouncing pattern (you can hear and feel it).
I can't quite put it down to being brake booster related, sometimes acceleration feels odd.

I am no expert, feels like it could be many things but I would appreciate any similar stories or experiences. Video attached of braking to a standstill.
1993 940 Auto, 230fb. I know the Cat is a bit cooked but no other major issues other than a minor coolant leak.

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jamesinc

Looks like it is hunting idle. Your TPS might need adjusting, if you turn the throttle by hand, right as it starts to move, you should hear the TPS click. Then click again when you close it.

Might also be a problem with your idle control valve, or possibly a vac leak.

Forg

Yes I’m with James in thinking a vacuum leak may be possible … correct me if I’m wrong smarter people than myself, but if you put it in drive & pull the handbrake on & let the foot-brake go & the idle is then happy, it’ll tell you there’s maybe an issue with the brake booster. I think. Maybe.

It doesn’t get driven infrequently enough for the fuel to be 3+ months old, does it? I get nasty idle with my aftermarket injection system, when the fuel gets that old.

dmc

Regarding the vacuum hoses, there are two on top of the throttle body that go to the charcoal canister, on a later model there may one, the twin cam only has one. With engine idling squeeze them with a pair of combination pliers to block them, if the idle changes then track back along the hose to find the leak. Also try the fuel pressure reg hose and the other hoses.

I assume your speedo is working normally.

Regarding the TPS, the test above will tell you if it is failing. No click sound (with engine off it is easiest to hear) tells you it is not working, a definite fail. A clicking sound implies it is working though could still be failing electrically. Have a look here and one of the pins is the idle switch, it will be 0V at idle and 12V when off idle, the middle pin is the earth. It is pin 2. https://ozvolvo.org/d/9733-9733

crawlvo

Thanks legends. I'll have a stuff around with those things today!

crawlvo

Had a look at the TPS - nice click after a few degrees of rotation (not immediate).

I did go and get my hands dirty:

new ignition leads (a few sleeves cracked)
new spark plugs
cleaned throttle body and IAC (+ electrical connectors)
Cleaned MAF sensor
replaced PCV box/hoses (deleted flame trap too)
replaced vacuum hose for fuel pressure regulator

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But, no changes to the idle. The worst of the lurching goes away after 15 min of driving, but it is always pulsing slightly when at a standstill.

Any chance it could be the fuel pumps? I haven't noticed any issues but I reckon when I got it roadworthied, they said the pumps were no good.

Major Ledfoot

crawlvo when I got it roadworthied, they said the pumps were no good

Why? Did they do a fuel rail pressure test? ObTip: A 93 will have a little valve on the fuel rail for hooking up a fuel pressure gauge for testing.

Checked your dizzy rotor button and cap? A sonofabeach to R&R, but they do wear out / get dirty. Especially at 400K+ km. They also suffer from corrosion inside the plug lead connector points.

Do you hear a hiss when you apply the brakes? If so: Brake booster. (been there / done that)

Have you changed the check valve on the brake booster? It's a 5-buck part. (ditto)

Also: Are all the HVAC controls working as they should - like, you don't lose air flow to the dash air vents under acceleration? If that is happening, that's a perished twin vacuum motor and thus a vacuum leak. Being a 93, it's about due to fail (have owned two 93s, one NA, one turbo.... and they both needed theirs replaced).

There's also a couple of check valves in the engine compartment that go and feed the HVAC too.

Edited to add: How's the igniter aka power stage - like, how old is it, and how's the wiring to it look? (on the LH front inner guard, near to the air intake box on NA)

crawlvo

Major Ledfoot Do you hear a hiss when you apply the brakes? If so: Brake booster. (been there / done that)

OK - absolutely. Not sure how I never noticed this, but a definite rushing air sound (not high pitch like a hiss, a bit lower) when braking. Modulates with how hard I am pressing the pedal.

crawlvo

From memory they said they just said the fuel pumps would need to be done - I had read of 'common' failures with the dual pump setup so didn't pry further at the time.

Dizzy seems a bit of a stretch with my tools - but I'll see if I can get to it.

RE: Hiss - Hearing a hiss in the cabin with the engine running? I can't recall anything, but will listen out.
Will look at those check valves.

100% issues with the HVAC vents - intermittent I believe/only noticeable at higher blower settings. I thought it was all the foam seals deteriorating (plenty ended up in my eyes when i first cranked the blower). Happen to have the part number handy?

Cheers mate

Major Ledfoot

crawlvo Happen to have the part number handy?

You need to fit the AC Delco ones, the Volvo ones are NLA - the dual port is AC Delco 15-71438. You do need to faff around a bit to get it to fit, but it will.

The dizzy cap is A Real Biach to remove, but can be done with a 10mm (or is it 8? can't remember...) ratchet spanner and a steady supply of swear words. (Mister Bear taught me the value of having a 1/4 inch socket set at one's disposal for jobs like this....)

Main fuel pumps get noisy before they die; in-tank pumps just croak. I reckon the 2 pump system is better than 1 pressure pump in the tank, but then I like hills and corners.

crawlvo

Legend. I'll put that on the list. Worth pulling the whole dash and resealing all the vents and flaps and whatnot? I've pulled all the lower panels and centre console a few times but never the actual dash. Could be a nice excuse to put some sound deadening on the firewall I guess.

I think a recent reply of yours (another thread) made me look at wasted spark, seems nice to fk the thing off entirely!

Thats the one. They (BMG) said the pump was noisy. And if the buzzing groan I hear when turning to KP2 is the pump priming, I'd probably agree?

Major Ledfoot

Pulling the dash itself isn't difficult, pulling the dash along with everything else you need to remove to get to what you need to R&R is a total crap of a job. I've been putting off doing my 945T's heater core for the last 14 months for that reason. Wished I'd changed it when I did the vacuum motor change. It failed just after my 960's heater core failed.... and replacing that was Trauma Plus.

You'll need a 1/4 inch socket set and a long extension for your 7mm socket to get to all those screws around the heater box cover. There are a LOT of them. If you can do the heater core while you're in there, do it - it will last another 32 years then.

crawlvo

rrrrright.... dizzy done, brake booster check valve done, new seals on the injectors. 1/4" socket set got a rare workout!
Cleaned up the grounds on the fuel rail too.

No real changes to the loss of power/lurching when braking.

Looking for a new heater core to justify taking the dash to do those leaky HVAC motors - makes so much sense now, when I'd turn the engine off and leave the blower on, the air would just go away (or not be on me face at least!)

I must have stuffed something up in the process - on a cold start the engine now freaks out a bit and revs up to 2k, down to 300 (almost stalling) and sounds generally unhealthy - but I think this is likely the clogged/scorched cat messing with the O2 sensor?

Forg

While I know zero about 940's, there's likely only one vacuum hose (or at least very very few) leading to the cabin ... you might disconnect it & plug with something (even just a bolt covered liberally in thread-tape and clamped with a good solid hose-clamp?), and see if the idle gets better?

I'm too lazy to scroll up ... 🙂 ... when you say "power/lurching on braking" do you mean while applying the foot-brake when at very low revs?
And does it go away if you use the handbrake instead of the foot-brake, say when the car's idling & standing still?

These cars are mostly 30+ years of old, could be vacuum-leaks in many things!

Oh, and on start-up I don't think most (older at least) ECU's use the O2 sensor for anything, using that input normally takes a while to cut-in (but again I don't know 940's or their ECU shens). Are you sure all the hoses are plugged back in correctly? Also I guess if you fixed a major leak already, then resting position for the throttle plate &/or idle motor may need adjustment in some way as maybe not as much air's getting into the engine so it's needing to crack the idle-air motor a bit more than it used to need to do ... maybe?

crawlvo

Alright - found the disconnected vac hose today on the heater control valve.

This was while swapping the brake booster, which the new unit, despite my best efforts, has a push rod that is too long. So, now the brakes are dragging a hair. The rod is backed off to the max and has a few washers to shim the MC out - still no good.

Reckon I'll have to get creative. Anyway, drives way better now and much less of the weird lurching and rough idle.

Always time to learn something new and also stuff something else up.

Major Ledfoot

IIRC, there were dramas when the booster was replaced in my 945T (93).

Where did you get your replacement brake booster?

crawlvo

Major Ledfoot

From Skandix, said it was OK for my model and ABS/RHD compatible, but oh well.

In the 'related items' Skandix shows 1064977 which looks like it would push things out too far and require lengthening of the pushrod, which is possible (it is currently as short as it can be). but then all the hard lines from the MC would be under a bit of tension...

I don't like the washers (means moisture could get in behind the MC), so am going to grind off 4mm or so from the end of the push rod.

crawlvo

Major Ledfoot I have an unrelated question about these hard lines (transmission cooler lines?) - they rattle on a cold start quite noticeably from the cabin. Video attached, and I reckon I can see there is a spot for a retaining clip of sorts.

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Can't find anything, would you happen to know if any solutions? I worry the fittings don't like the rattling (I also just don't like the noise)

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Major Ledfoot

About the 'intermediate section' aka "Adapter, Master brake cylinder"

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It's item [15] in this, Drawing 54500 on Group 52, page 1120, PDF page 1114 of the 940 -93 parts book.
That's Volvo part number 1330315, which you linked to at GCP.se, for e71.44 which Skandix has it for e88.88 including the Gerry Harvey Failed Business Model Protection Tax of 10%.

The ABS booster [10] lists four OE part numbers!
3516093-6 = 1991. 2X8" DBA (ABS up to 91 only)
3516094-4 = 1992-. 2X8" DBA (non-ABS, and ABS 92+)
3530181-1 = 1991. 10" DBA (ABS up to 91 only)
3530182-9 = 1992-. 10" DBA (non-ABS, and ABS 92+)

Then it refers you off to Group 52, page 1155, PDF page 1119, and Drawing 66181 for the master cylinders.

IIRC (because it's over 8 years ago now) the replacement booster I got from FCP for my 93 945T wasn't a direct fit, either - the shop had to do some jiggery-pokery with the push rod to make it fit.

I don't recall seeing this adapter on my master cylinder, but it may be there; if there isn't one, I'll come back and edit this response after I've had a look.

With regard to the rattling oil cooler lines, it looks to me like [8] [9] and [10] are missing from your setup, and the exhaust guy has done something odd with the mounting bracket in the past, but maybe others can comment?

crawlvo

Legend, RE oil cooler lines that would be it, just need something like part [9] and a fixing method. Wasn't sure if there would be some rubber involved!

I see what you mean with the variety of boosters - this (93 ABS NA 945) had no adapter/intermediary part between the master cylinder and the original booster.
After grinding and reshaping the end of the pushrod I am happy with how it feels - a tiny bit of travel in the pedal before the brakes kick in. Easier for gentle braking in start-stop traffic, I think.

In that diagram, it looks like the ABS booster in that diagram is indeed "thinner" hence why it would need the adapter plate.

Major Ledfoot

crawlvo In that diagram, it looks like the ABS booster in that diagram is indeed "thinner" hence why it would need the adapter plate.

Yeah, the 10 inch DBA is thinner, but note also there's different master cylinders too. IIRC the 10 inch was used on 16V cars. The book doesn't distinguish what's used on NAs, turbos, 16Vs, 6-potters, or Dweasels.

carnut222

crawlvo Pretty sure I have one of those oil cooler line retaining blocks. Happy to post it to you. Lemme know.