740 - B230k idle woes

[Laird Scooby]

Originally Posted by islipaway

Sorry I can't reply to your PM until I make a few more posts!

Obviously that was the post that changed things!

PM replied to!

[islipaway]

Belt looks decent, couldn't get the cover all the way off as the lowest cover bolt seems to have seized on but it was tight and looked new/decent. Can't rule out it being aligned incorrectly but can rule out worn/slack.

Today I gave the car some good old high revs and it seemed to run better after that for a while! It rarely gets a chance to get over 3k revs with my placid around town driving.

Could be related to the dizzy/hall sensor? I replaced the cap/rotor as they were pretty worn looking. The wire that comes out of the sensor in the dizzy was bare at one point, I sealed it up but, I wonder if water made it's way down and has corroded the connection between the dizzy and the wire.

I tried to gently remove the connector but wasn't able to and didn't want to break it as I think it's quite fragile.

Where does that wire end up? It doesn't seem to be one that goes to the bell housing, it gets wrapped up in a harness and goes into the firewall on the passenger side.

Would this car have a radio surpression relay? I've read that can lead to issues/be an easy fix but not sure if it's relevant to this model.

Lots of Qs! Sorry.

[Laird Scooby]

At least the cam belt is in good condition then!

As you say, it doesn't rule out mis-timing it but at least it's unlikely to either break or shred teeth anytime soon.

To the best of my knowledge and memory, if you have a Hall Sensor dizzy you won't have the flywheel mounted sensor and there's no real need of it on a carb or even a K-Jetronic car. The Hall Sensor will either work or not, unless a wire is broken and sometimes making contact - you did the right thing sealing the wire where it was bare anyway!. Had that same problem on a Mk2 Cavalier many moons ago - it would suddenly just cut out for no reason. A few minutes later it would restart and go for 200 yds or 200 miles without doing it again, it really was a random occurrence!

Radio Suppression Relay - originally fitted in the supply to the injectors to remove back feeds of emf as the injectors were switched off which was causing interference on the radio. Highly unlikely yours has one in that case although Volvo may have been clever and renamed/repurposed it as the Auto-Choke Heater supply relay. Not saying they have, just might!

Sounds like the Italian decoke helped somewhat? Maybe a good blat up and down the nearest motorway (not the M25, you won't get out of 2nd gear! ) would be a good idea. If you constantly run in and around town, you never really get to open it up to burn off deposits that accumulate on the pugs, this was well known for causing misfires back when carbs were commonplace.

[islipaway]

Anything specific I need to be aware of with replacing the intake manifold gasket? Or just unbolt it, clean both surfaces and put the new one in dry?

[Laird Scooby]

I'm pretty sure the inlet manifold is heated by coolant so there will be coolant inside it and one of the heater matrix hoses connects to it if memory serves.
If i'm right (and i can't remember if i am) then you'll have to drain the coolant down before removing the inlet manifold. Then as you say, clean the mating faces and refit with the new gasket.

If spraying WD40 hasn't made enough difference while the engine is running then i don't think this is your problem

[islipaway]

I've got a new idea!

Today I noticed that when steering with the clutch in the idle would drop. Now I think it's normal for the pump to cause the idle to drop a bit at full lock but this was at less than that.

The fluid seems to be up to the max level, so if this pump is dying, or I guess if the alternator is dying the hunting/dropping idle could be related to either of these putting extra load on the engine?

[Laird Scooby]

Not being funny but it's doing that regardless of steering input, alternator load or anything else.
Being blunt about it, you're clutching at straws for an "easy fix/obvious solution" now.

I still think it's either a vac leak (but you seem to have exhausted the probabilities on that) or it needs tuning, possibly timing is out (including the cam timing) or the carb has been tinkered with so much the idle air screw (that controls the idle speed) is too far in reducing the idle speed below an acceptable level or the mixture screw is so far in it's running as lean as a hunger striker on the Slim-Fast plan or both.

This can cause other problems with the running as well, all the way through the rev range.