Hi
I have a 1977 nz new xj-s v12 that is having a few issues. One is that it will start no problems cold but after awhile it will idle rough and splutter sometimes backfire. I have replaced a lot of things to no avail. I also notice that when you turn the air con on doesn't increase the idle as it should do. Can anyone shed any light here for me... Thanks

 

When warm and running poorly, jump out the connector for the Coolant temp sensor ( Port side at front of water rail ). If it's a bad CTS this should settle her down.

 

As well as the CTS bridge I would check the following:

Fuel Pressure. You have 2 FPR's, and the setting is fiddly at best. I use 2 gauges, and set them at about 30psi, HOWEVER, one of mine just luvs 29psi, and the other is sweet at 32, so the ABOUT, is just that. It is no different to adjusting the mixture on a carby,

The MAP, on the LH side of the radiator top panel is now a known issue due to age, and they are very hard to find. They are adjustable, and that can sort a rough idle if you are very careful, due to the adjusting thread being very coarse, so a little movement means a lot.

The throttle switch is probably out of adjustment. That is a mongrel to set up, and patience is a must with that item.

A build up of black goo inside the throttle bodies, so a solvent soaked rag, and wipe them and the discs, until they are clean.

 

Grant, what's the MAP?

 

Hi Steve

Maybe its some sort of sensor?

 

Being D Jetronic, it is a seperate item.

Its the alloy casting that has a vac supply, and a wire loom, and converts vac signal to electric for the ECU.

I think it stands for Manifold Absolute Pressure Sensor.



Has twin bellows inside, like a Barometer, plus electrickery stuff.

 

Ah, MAPS not MAP!
Thanks.