Chasing a slightly lumpy idle...still

[AllHailKingVolvo]

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!!!

[bob12]

Have you cleaned the plug on the ignition amplifier?

[Laird Scooby]

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.

[AllHailKingVolvo]

Originally Posted by Laird Scooby

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.

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!

[mjk164]

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.

[Laird Scooby]

Originally Posted by AllHailKingVolvo

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!

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! 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!

[AllHailKingVolvo]

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...