Idle control valve query

[Phil-T4]

Originally Posted by Mogmike

Hi Phil.. I'm not sure how you can fix a compression issue properly without taking the head off and checking the valve seals and seating so any pointers would be welcome. I have put in a Wynns oil additive to help but I'm not convinced that the 3 point difference would make much change to the tick over. It was fine before and it didn't run far at all when the gasket let go.. I got it towed home. The biggest difference is when I took the pipe from the idle control valve off and air was freely flowing into the throttle body. It increased the tick over speed a tad and was noticeably smoother at tick over and brighter to drive. You also noted a miss fire on one of the ht connections and maybe I should look there as well. It is frustrating not being able to adjust air flow and mixture... Having to wait for the ecu to learn any change.. Without a T4 to set anything is crazy for an old school Morgan owner like me.. Any thoughts would be welcome.. Thanks.. Mike

Hi Mike,
Unfortunately to fully correct it the head will have to come off, valves lapped and tested for a good seal, valve lift checked as if the cam lobes are worn they won't be opening fully, piston travel checked, piston ring wear etc etc.
I did set the iacv for you and also checked the injector open times, I think they were all around 2.3ms, mixture is not user adjustable, the ecu adjusts very quickly to changes, this is called the 'short term fuel trims', long term are the adapted (average) values based on the short term.

The coils had corrosion on the tips and were making poor connection to the plugs, we did clean them up for you and it certainly reduced the misfire rate but not cure it, this is why a compression test was carried out and found 2 & 3 noticeably lower than 1 & 4.
Opening the throttle and allowing more air and fuel in will always appear to make it run smoother.

You could try and get a leak down test done and this will show if the valves are leaking or the piston rings.

Good luck with what ever you decide to do.

p.s. Don't forget the timing was out which can cause a problem with valves and seats so although they may have been OK before, don't take it for granted that they have a good seal now.