What is this please?

Hi everyone. I have a car (a '68 Aston DBS) which has been given an AJ16 from a 1995 XJR Supercharged. I have have every thing out/off to cosmetically refresh and check for function. Some things were carried over but not actually functioning and some things I do not understand the purpose of as I am not a trained mechanic.


One end connects with the breather tube from the top of the cam cover. It seems to have a by-pass for what seems to be a by-pass itself. Although the ECU from the donor was used, most functions were not active as the timing was changed to a distributor from a XJ40. Any information to tell me what this system is, what it does and can it be removed would be appreciated. Thanks.

OK, I’ve been doing research on this and now I know more. (Yes, I know I should have done it before posting, sorry). So the large unit is a Idle Air Control Valve (IACV) (Lucas Lucas 73377E) and the smaller one is a Supplementary Air Idle Air Valve (Lucas 9AV 73298A). I still don’t know if they came from the donor X300 XJR or were sourced from other Jags - if you know that would be helpful. I also don’t know why two valves are needed, could someone explain that perhaps?

Normally these would be operated by the ECU but as so many sensors were not working to simplify the overall system and make the engine work, the previous owner who did the conversion added a switch to the dash to allow for cold starting acting like an on/off choke. The supplementary valve was connected, but the IACV was not connected to the loom so was not working. My electrician is going to make everything work as it should (we hope) and delete the switch on the dash. We have a new ECU from Emerald and all sensors will be reinstated. All good fun…