Hello everyone

I’m having a few problems (I know very surprising). First: my Idle. The car would start perfectly but once warmed up and ready to go the RPM’s would jump up and down from 500 up to almost 1800. I would not stop until I put the car in gear (either forward or reverse). on top of that while I’m driving if I take my car off the accelerator the jumps while downshifting. The other problem is its very hard to start when hot. It cranks, start stumbles then dies. It takes about 10 tries to where it will eventually start. The rpms at 100 and slowly rise as long as I keep tapping the accelerator.

Second problem: Today I noticed my exhaust (right tail pipe) wasn't blowing as hard as the left. Also, when I had a look under the hood, one of the ignition lead rubber boot going to the Distributer cap was melted and part of the cap tower where it plugs into was melted as well (Marelli Ignition)
I just ordered a new cap. Can some tell me what is happening here? I'm afraid something bad is on the horizon.

Evan
1989 Jaguar XJS Convertible

 

Evan,

Marelli car running odd, DO NOT DRIVE IT.

My experience with the Marelli cars is almost zero, only 1 where I abode.

You will need to sort the cap and rotor, and do the rotor modification (someone will explain). It sounds like it is running mostly on 1 bank, they do that, and cat fires are real close by, NO joke.

The pulsating idle may be a myriad of things, BUT, until that cap and rotor are sorted are the least of your worries.

Some of the idle items may be:

AAV stuck (common).
Black goo around the 2 throttle discs (sommon).
TPS gone AWOL, (common now with age).
Throttle cross rods incorrectly adjusted (common due to slack maintenance).
PCV valve worn out (again sad maintenance item).
MASSIVE vac leaks, more like HEAPS of little ones (maintenance lacking again)

The list is LONG, so I will stop for now.

 

I appreciate your input. I've taken off the AAV tested it and it works perfectly opens in hot water and closes in ice water. Tested the tps it was installed wrong. Now reading .34 and increases smoothly. No vac leaks anywhere. Throttle bodies clean as a whistle. Just ordered a new cap, rotor and plugs going t do the rotor mod with silicone sealant. Would it help after I replace the ignition components to gut the cats? I'm thinking the right exhaust may have melted internally?? Is it possible? The idling problem is driving me crazy. Anything else I should check in regards to the idling problem.

Thank again,

Evan

 

Ummmmmm, I'm confused.

The AAV should be 100% closed in hot water, and open when cold, so maybe a typo???.

I have no idea of USA Marelli cars, but the 1 I had doings with here had a micro switch on the top of the LH throttle rod bellcrank, just atop the LH air cleaner base, and it has a significant influence on Marelli idle.

Not sure if the Marelli fuel ECU, the one in the boot, has an adjustment for idle fuel mixture like the earlier cars. I would "guess" it does, and that would certainly allow some "trimming" of the idle fuel.

The gutting of the cats is a top idea. As they do fail and clog with age.

 

I have a vague notion that there is a cut out if idle gets too high and then it starts all over. There is a thread on this here or in jaguarforum.co.uk. When new items are in place I'd revisit the throttle butterflies. Then adjust the AAV. I haven't looked at my (Marelli) ECU for a long time but I think there is very little in the way of adjustments available.

 

Until you get the ignition system in order, you will not be able to do anything good to tune the car. Install the new cap and rotor, check to make sure the catalysts have not melted down, then see what the engine does.

Until both banks are running properly, the AAV and other items are not going to be performing as designed. With one bank essentially dead, it's no wonder the car hunts for idle.