87 XJS idle/throttle response problems
#1
87 XJS idle/throttle response problems
I recently acquired a 1987 XJS that has been sitting in a garage for the past 15 years with 69K miles. My local garage who has a very competent mechanic on staff has done quite a bit of work to get this beast to run. The most recent repair is replacement of the distributor & pickup coil, new plugs and set timing and new AAV. After this, below is the newest problem. If anyone has some ideas on where to look for troubleshooting I would appreciate it.
Thanks,
Bob
Thanks,
Bob
Here we are with the Jaguar, we have now removed the distributor and confirmed proper operation of the mechanical advance, vacuum advance and all components in line with the ignition system are operating normally. The current issue is that the idle is low and will not respond to applying the throttle there is a major delay, the engine will ping and then respond to the throttle spiking the rpms, the rpms will hang high and then settle back to spec, and then repeat. We have attempted to set the timing at base, advanced and retarded and still with the same result. There is an idle speed control unit though tests show it is good. We have posts on IATN and are continuing to research other potential issues with the car. Keep you posted as to the progress.
#2
Join Date: Mar 2008
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A couple quick thoughts....
I hope they're running fresh fuel !
After 15 years of non-use there are probbaly a whole slew of things that need attention.
As for the issue at hand, if the car was in my garage I'd be tempted begin by to making sure the throttle bodies were clean, the throttle blades set at the proper .002" gap, and the linkages synchronized....and check that the throttle bushings haven't crumbed away. Sometimes the easy stuff actually fixes problems
An oscillating idle can be caused by extra air being drawn in. This increases the rpm *until* the ECU cuts off fuel. Then the engine speed drops way down....at which point the ECU turns the fuel "on" again, and the engine speed increases. Then the ECU cuts off the fuel once again....repeat, repeat.
This often points to an AAV problem...but you say it was already replaced. So, extra air might be coming in from elsewhere. One thought: if any of the air-cleaner-to-throttle-body-bolts are removed the engine speed will increase quite a lot!
Cheer
DD
I hope they're running fresh fuel !
After 15 years of non-use there are probbaly a whole slew of things that need attention.
As for the issue at hand, if the car was in my garage I'd be tempted begin by to making sure the throttle bodies were clean, the throttle blades set at the proper .002" gap, and the linkages synchronized....and check that the throttle bushings haven't crumbed away. Sometimes the easy stuff actually fixes problems
An oscillating idle can be caused by extra air being drawn in. This increases the rpm *until* the ECU cuts off fuel. Then the engine speed drops way down....at which point the ECU turns the fuel "on" again, and the engine speed increases. Then the ECU cuts off the fuel once again....repeat, repeat.
This often points to an AAV problem...but you say it was already replaced. So, extra air might be coming in from elsewhere. One thought: if any of the air-cleaner-to-throttle-body-bolts are removed the engine speed will increase quite a lot!
Cheer
DD
#3
#4
Join Date: Mar 2008
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Ahhh. Ok. I misunderstood what this meant:
"....then respond to the throttle spiking the rpms, the rpms will hang high and then settle back to spec, and then repeat. "
I'd go back to what I mentioned about throttle gaps, etc. Gotta start somewhere....and this is one of the easiest places
One of the frustrations on these V12 Jags is that it is SO easy to inadvertantly cause a problem with Widget-B while working on Widget-A. Close working quarters combined with a plethora of brittle wires and hoses is a recipe for trouble. It's not a matter of being careless or ham-handed. It just happens.
Cheers
DD
"....then respond to the throttle spiking the rpms, the rpms will hang high and then settle back to spec, and then repeat. "
it is when the throttle is applied that this problem arises.
I'd go back to what I mentioned about throttle gaps, etc. Gotta start somewhere....and this is one of the easiest places
This started after they replaced the distributor and set the timing.
One of the frustrations on these V12 Jags is that it is SO easy to inadvertantly cause a problem with Widget-B while working on Widget-A. Close working quarters combined with a plethora of brittle wires and hoses is a recipe for trouble. It's not a matter of being careless or ham-handed. It just happens.
Cheers
DD
#5
#6
#7
Join Date: Mar 2008
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Not to cast aspersions on your mechanic or to elevate XJS repair to the level of out-n-out black magic....but even very experienced mechanics don't know the tricks of *every* car made.
If you tell us that your guy has umpteen years of "Jag V12" work under his belt we can problably dispense with a great deal of speculation. :-)
How would this contribute the to the stated problem?
Well, if he set the timing at idle speed rather than the required 3000 rpm he'd probably end up with way to much advance....which could account for the pinging. Plus, increased initial advance can increase the engine speed/idle speed.
In any case, when trying to ferret out mysteries there's no point in adding new variables....such as ignition timing being incorrectly set.... to the mix
Cheers
DD
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