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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Jaguar
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Jaguar XJS Classic Collection: I have a well maintained 90

Customer Question

I have a well maintained 90 XjS 5 k since new wires plugs and injecter loom
Starts up immediately when cold or hot
But of late when warm a miss Not cold or warming up. Smooth accereleration , hate to look for bad plug or injector any thoughts?
Submitted: 2 years ago.
Category: Jaguar
Expert:  Juan Crespo replied 2 years ago.
Hi there. Welcome to our site. Well, I don't think you'll need to look for a bad plug or injector; instead, run the engine 'till warm; turn it off and locate the auxiliary air valve (see attached graphic). Block off the air/vacuum hoses. Start the engine and let it idle. If the idle speed smooths out, the problem is the valve. If no change, check for a leaky vacuum hose or gasket allowing unmetered air into the intake manifold. Best Regards.