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!!!