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Matt, Engineer
Category: Jaguar
Satisfied Customers: 21860
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Jaguar XJS 2+2: I have a 96 xjs 4.0 (aj 16 engine) with a poor

Customer Question

I have a 96 xjs 4.0 (aj 16 engine) with a poor idle (engine shakes) Vehicle is difficult to start. Took vehicle to a repair shop that works on jags (a lot of jags were there lol)! It was found that 4 coil packs were bad. Did not ask if any codes were stored in the ecu. Replaced the four with aftermarket coils and one oem coil that was good that I had lying around) to keep the vehicle running. The vehicle idles poorly and I hear an intermittent "puff" form the engine. The check engine light never was on. I removed the throttle body from the intake and noticed there was oil at the intake opening. I also removed the MAF sensor and the housing and noticed the plastic elbow was oil coated. I cleaned the throttle body and I will install it this weekend. What is the torque value for the throttle body to intake manifold? What type of sealant should I apply to the throttle body and the bolts? (some type of sealant was on the throttle body as well as the holes on it) Once I install the throttle body and maf sensor, and the plastic elbow, where should I begin looking for the possible causes for the poor idle and performance? As for codes (if any) It is my understanding that "P codes" are not jaguar specific. In may I put a scan tool on the vehicle that can read dtcs for my model year jaguar and none were present
Submitted: 2 years ago.
Category: Jaguar
Expert:  Matt replied 2 years ago.
Hello the sealant on the bolts was just a thread-lock , probably loctite 270I'd say the issue may well be a dirty MAF meter so its worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residueOn no account touch the sensor wires with anything physical as they are extremely fragile This could also be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Expert:  Matt replied 2 years ago.
do you still need help?