Lack of power & erratic idle - Pulling my hair out!!!

[Paul240480]

1991 480 Turbo Auto with 144k miles.

For about the last 15k miles, every 2-3k a lack of power and majorly erratic idle occurs. Revs going from 3-20k over & over. Normally I find the plugs blackened/sooty & a quick clean up sorts it.

To fix, so far I've carried out the following:
Cleaned the Idle-Valve (brill 'how-to' on 480-europe site).
Replaced perished pipes on Turbo intake.
Replaced perished braided hose under throttle body.
Replaced air filter
Replaced HT leads
Changed plugs (Tried Champion, tried BERU - now on NGK).
Air Mass Metre is only 5 yrs old & I've tried altering resistance.
Speed sensor has also been replaced & resistance is spot on at 220 Ohms

Not checked yet, but I reckon I'm gonna find the plugs sooty & black AGAIN when I look.

I'm now stuck as to what to try next. Thinkin' about chucking it in to a garage (wallets trembling) Got MOT on 29/08 so will probably wait the result of that before spending.

So have any of you kind soles got any suggestions please?

Thanks
PS I've posted this on 480Europe too but no suggestions.....yet.

[Paul240480]

Okay, been waiting all day for the rain to stop............ managed to get one plug out just (before the heavens opened again) and yes it is as suspected as sooty as can be.

Had one reply on 480-Europe suggesting Lambda Sensor is probably duff

[Baffler]

Poor idle can be caused by perished rubber pipes joining the carbon canister which is located in the o/s front bumper. Pop off your indicator/DRL lens and you can see in with a torch. When I discovered mine, at the bend where it joins the canister, it just fell away in my hand. Don't think it would make your plugs foul though? Possibly getting to much fuel? As suggested a possible damaged lambda confusing the engine management.

[Paul240480]

Ta Baffler, will check that out too. All 4 plugs were indeed blackened. I've removed the battery & tray in order to get to the Lambda leads to carry out a test, but so far cannot find the flippin' things!

[Paul240480]

Have now checked out the pipes by the carbon cannister thing, they all seemed okay & still very flexible.

I spent this morning testing the volt readings from the Lambda & at first got a steady 0.6 or so volts. Should be a fluctuating reading much much lower.

A reading of 0.8 is a sign of an air leak or incorrectly set MAF sensor. Now I'm pretty sure, from previous work that an air-leak is not the problem. So set about re-setting resistance at the MAF. I've ended up leaving it at 900 ohms with a volt reading at the Lamda down to a steady (ISH) 0.5. The maf seems to 'top out' at 930 Ohms.

So I'm not getting the correct 'steadily fluctuating' reading at the Lambda no matter where I set the MAF. And I'm not at all sure what this is telling me. But having left it ticking over for 15-20 mins it was idling smoothly however, its done this before so I'm not holding my breath!!

So, with the Controle-Technique (MOT Here) due on Friday I've decided to leave it 'as is' at the 900 Ohms (MAF) and see what the 'CT' throws up. If we get through or fail on minor stuff then I'll think again on where to go from there.

Thanks

[Paul240480]

So far so good on the rough running score. MPG is up to 26.6 after two or three shortish runs, so not bad for a Turbo auto. I'm hoping it rises to around 28 or so.

All set now for the Controle Technique (Frenchy MOT) tomorrow. If get a pass thenI've got another two, at least more years of 480 trials & tribulations LOL

[Baffler]

Fingers crossed. Best of luck...

BTW...you should be getting around 32 to the gallon but I'll stand corrected. Those turbos are fairly economical.

[Paul240480]

:thumbs_up: with Controle Technique!

A few advisory notice though.

Minor Corrosion to rear brake pipes.
Rear Discs nearly worn (Already aware of that)
Minor leak in P/steering system
Dipped-beam too low!
Nail in a tyre:realmad:
Minor play in F/N/S balljoint
Oil leak in engine (already aware & its minor, or normal for one with 144K!!)
AND
Excessive play in F/N/S wheel-bearing.

Now with this last point he asked me if it had been me that replaced the front discs (I did about two weeks ago). He then said that I had not tightened the bearing up when refitting & that it is part of 'the job'. Now in 'paynes' it does not mention anything about the bearings in the how-to replace discs.
In the bearings 'how-to' bit it says if play is excessive to replace.

So does anyone know if the bearings can be simply tightened. I guess, if yes it would be a simple case of wheel off (axle-stand) & tighten the big nut in the centre of hub?

Still, I'm chuffed to nuts with the pass!

Ooh, Baffler, I've never obtained over 30 (save for long runs of which are few & far between these days) & it is an auto which may make it suffer a tad more than a manual turbo?

[Paul240480]

Just had a peek, to check everything I 'touched' was still tight & yes it all was as 'tourqued' when I replaced the discs.

The wheel defo has movement at '6 o'clock - 12 o'clock' & at '3 o'clock- 9 o'clock so guess that would suggest wheel bearings & 'Mr MOT man' is not exactly right? Still only advisory though & he was happy to pass it for two years.....

Opps seem to have taken me own topic 'off topic' here:err:

[Baffler]

And even more off topic...

The f/n/s bearing nut is a common fault. They become loose after being removed once. Volvo advise that you should replace it with a new nut once it has been taken off. I don't know the name for this type of nut but it's the "one use" type.

If I were you I'd leave the road wheel on, remove the hub cap, take off the nut (think it's 32mm), put a good dose of threadlock on the shaft, screw back on the nut, have someone sit in the car while it's idling and press firmly on the brake pedal, tighten your nut a little above the specified torque and see if that does the trick.

Hopefully it'll save you having to replace the bearing.

[Paul240480]

Sounds good, will give that a go methinks::thumbs_up:

[Paul240480]

Still wobbly so reckons it's a replacement job.

Idle still smooth:thumbs_up:

Hopin it stays that way!

Thanks for all the replies.

[Baffler]

Ahh that's a pity... I bought the NS front bearing from the main dealer and had a local mech press it in for me as it can turn into a difficult enough job if you haven't the right equipment. It might be a good time to replace with a new nut too.

IIRC...the bearing was about €40 (3454197)

Good luck with it.

[Paul240480]

Well, being a 'tight wad' I just had to try Bafflers suggestion again & it's sorted now, no more movement. Perhaps letting it run for a few miles after the last attempt has helped things to settle snugly.

:thumbs_up: Baffler!

Idle is still, so far behaving.

[Baffler]

Glad to be of assistance :) Hope it lasts for some time to come.