Chasing a slightly lumpy idle...still
 

Hi all,
I’ve dipped in and out of threads here, mentioning my slightly lumpy/shuddery idle issue with the B200F in my 744.

To date I have done the following:

New plugs
New HT leads
New coil
Checked all earth straps
Replaced fuel filter (Bosch)
Replaced rotor arm (Bosch)
Replaced dizzy O rings (Volvo)
Cleaned dizzy cap and filed clean all contacts

Today was fuel filter and distributor day...the dizzy was in a horrible state, the rotor arm was burned and disintegrating, and the cap was very oily and filled with fragments of the old rotor arm, which had clearly lunched itself over time. All the contacts were black with burned oil and the whole thing looked a mess. I pulled it all out, cleaned it thoroughly, filed all the burned mess off the contacts and replaced the O rings and rotor arm. The contacts have a recess in the middle of them from wear and heat damage but otherwise they came up well and the cap isn’t too bad. I’ll replace it eventually but it’ll do for now.

I reassembled the car and fired it up, and to my surprise (I was sure the skanky dizzy was the culprit) the slightly lumpy idle remains. The car is more powerful and perky now which is a nice side effect, but the idle issue is really annoying! It’s no dealbreaker but I just want to sort it.

I’ve just put a bottle of Forte injector cleaner in 3/4 of a tank of fuel, and will be doing a 70mi round trip tonight and a 250mi round trip on Sunday. Keeping my fingers crossed that the trade quality injector cleaner and some miles will help things along.

A friend of mine did his AA apprenticeship on 7/900 series cars many years ago, and he suggests that it’s possibly down to deteriorated injector O rings, so I’ve ordered some which will be here next week. The in-line fuel pump is strong so I’m not too worried about that at the moment, although I may change that and the in-tank pump just to cover everything off.

Thankfully the car drives like a peach and I’m enjoying gradually making it just right with as much DIY as possible. It’s been expensive and time consuming, but I have no plans to part with the car so it’s worthwhile to me...as long as I can get the @?&£er to idle smoothly!!!

Have you cleaned the plug on the ignition amplifier?

The "O" rings are a possibility Phil, use some silicone grease (not sealant) on them to help them "find" their pressure-tight position and slip in easier.

Have you checked the Throttle Position Switch to make sure the idle switch is operating? Sometimes called "Throttle Closed" switch as well.

Also - B200F - i know it's a 1990 car and therefore too early to have a mandatory cat but does it have a cat and Lambda sensor? If so, it's possible the Lambda could do with renewal.

However, if the lumpy idle is present from cold, ignore those two ideas. They will only be relevant on a hot engine.

If it's present from cold, have you checked the large diameter hose between the throttle body and MAFF? Even a pinhole in this can cause problems!

I think you may need to renew the dizzy cap and rotor arm though, it sounds compromised and if so, even after cleaning, it will still be compromised. ;) :D

Thanks Dave, I did renew the rotor arm but not the cap-I’ll order one and fit it next week. It’s definitely less than ideal, even after cleaning. The lumpy idle is indeed from cold-I’ll check the large hose to the throttle body, I think the joint where the pipe to the PCV mounts is a bit ratty and may well be letting air in. I still have yet to clean the PCV on this car, the flame trap is done but the actual box itself needs to come off and have the usual scrub and flush out.

I wonder if the MAF would benefit from cleaning too?

It does have a cat and lambda sensor, i will renew it just to be on the safe side. I’ve thought about de-catting the car but that’s for another discussion!!

On the upside, I’ve just got back from tonight’s gig which involved a 70 mile round trip-I put a bottle of Forte injector cleaner in the tank before I left, and the change in throttle response and general power is fantastic. No more working my way down the box to deal with hills, loads more power and smoothness. No difference to the idle, but driveability is much improved.

I’ve noticed since changing the fuel filter the in-line fuel pump has become a little noisy, so I’m now pondering changing that and the in-tank pump to make sure there are no issues with fuel pressure...the fun continues!

I would support what Dave has suggested; the throttle position switch spends most of its life in and around the closed position and is a regular failure in that area i.e. poor idle. I would deal with that first and then the Lambda sensor but try to get a new original Bosch type.

You've pretty much formed a chronological plan of attack with your post Phil!

1. New dizzy cap

2. Inspect/clean/repair the PCV system - don't overlook the flame trap, it's likely to be dirty again! :speechless-smiley-5 Also don't forget the manifold stub for the small bore pipe.

3. Clean the MAF - disconnect both hoses from it, spray carb cleaner in both directions through it Don't use contact/switch cleaner, first it's not really the right mix of chemicals, second it often contains a lubricant which remains afterwards on the sensing wires and needs burning off before any improvement is likely to happen and third it's not really that effective at cleaning them.

4. Wait until you've got the cold idle smooth before changing the Lambda and cat. The cat could be blocked causing a general excess back pressure situation which can cause rough running at idle but not when it's cold as the cold idle running is open loop. Same goes for the Lambda.
Decatting would be perfectly legal as it's a pre-92 car and therefore doesn't have to have a cat. Would also bring an improvement in power and economy.

5. Good news the Forté has improved things! Before changing the pumps, check all the rubber hoses between the tank and pump for perishing - a perished hose can let air in as well as fuel out. This can make the main pump noisy.

Out of that little lot, i think 1 and 2 will have the most effect on the idle. Nearly there with a bit of luck! ;) :D

Thanks Dave, I will get onto that today!

I’m debating what approach to take to de-catting the car as obviously the lambda sensor is a consideration...i’m tempted to remove the guts from the existing cat housing and refit it, but I could cut a hole for the lambda on a straight pipe and weld a mounting nut onto it if necessary. I’m not the world’s greatest welder but I do have the gear and the (possibly misplaced!) will to do it...

Where is the Lambda situated on the B200/230 engines Phil?
Most Lambdas are fitted in the exhaust manifolds so you shouldn't have to fit a new boss for it in the decat pipe. However i've done a bit of digging and found a couple of things that might be helpful :

http://webcat.klarius.eu/catalogue/images/uk/960142.png

http://webcat.klarius.eu/catalogue/images/uk/960097.png

(There is another system that covers different times and the same engine sizes, omitted it for clarity and lack of relevance)

If you look at the first one, that should be the system you've got, showing the Lambda sensor in the front end of the cat - judging from your comment, i'd guess you have this arrangement?

Compare the two systems from the cat back, they're identical. Whether you could mate the non-cat front box to the cat-type front pipe i'm not sure, it appears to be a different gasket/sealing ring but if you could it would save the cost of a front pipe if you chose that route.

In the original front pipe, there appears to be one or two "Lambda bungs" fitted, in other words, remove one or other of those and you could resite the Lambda relatively painlessly, for your wallet at least!

If all else fails and you change the front pipes and box, instead of welding a Lambda boss onto the new front pipe, you could use something like this :

https://www.ebay.co.uk/itm/50-mm-2-E...W/183370967288

https://i.ebayimg.com/images/g/PE0AA...vH/s-l1600.jpg

Cut a short piece out of the front pipe (guessing about 2" looking at it), slide it into place, clamp it up and fit the Lambda. I think that's the right size for the front pipe, other sizes are available so please check before ordering!

Alternatively, if those aren't Lambda bungs/bosses on your existing front pipe, you could fit one of those with your Lambda, remove the cat and chisel its innards out, refit and job done! Might sound a bit tinny though, degutted cats often do.

There are other methods of doing all this, that's probably the cheapest and easiest though. ;) :D

Super helpful stuff, thankyou!!!

The lambda on my car screws into the cat, as per the first Klarius diagram. Those cat delete pipe sections with the Lambda boss are a brilliant idea! I’ll order one of those. I’ve replaced the back box as the baffles had disintegrated, but it’s blowing a little at the joint, as the “up and over” pipe in front of it was fairly rusty at the joint. I cleaned it up as much as poss but it still isn’t a very good joint, so I’m thinking a new up and over plus centre box are in order, and I’ll decat in the process.

You're welcome Phil - the over-axle pipe is on offer on ebay :

https://www.ebay.co.uk/itm/Replaceme...w/141000975527

Please don't buy all 10 though! :lol:

https://www.ebay.co.uk/itm/1x-KLARIU...-/141678195344

That's the middle silencer too.

That clamp-in section with the Lambda boss are designed as repair pieces and may not be long enough to act as a decat pipe on their own. Also looking at the diagram, it suggests the O/D of the cat section is 54mm or 2 1/8" so the one i linked to won't be the right size from the look of things.