Mark,
Okay, the coils are plugged in correctly.
The engine idles well then it seems that a complete ignition failure momentarily occurs.
Most of the times it will recover in time to not stall completely.
Do you know if your car will run without the IAC and/or the MAF hooked up?

This seems more of a temporary loss of 12 volt power to the system.
RagJag

 

With a bit of reluctance I'll throw something out for consideration. I've hesitated until now because I didn't want to muddy the water with discussion that might not be applicable. However, what you've mentioned bears a striking resmeblance to a recent experience with my XJR.

In brief.....

For several weeks I battled a "misfire at idle" problem. Not a generally "rough idle", mind you, but a very pronounced misfire....almost as though 12v supply was being interrupted to one or more of the coils. Lots of investigating ensued, with appropriate levels of frustration.

On nothing more than hunch and whimsy I changed spark plugs. The existing plugs looked perfect and were only a few months old...but I changed them anyway. I also changed brands at the same time....from standard Champions to standard NGK.

(By "standard" I mean not iridium, not platinum, not v-power, not double-copper-super-wazoo whiz bangs. Just ordinary standard issue spark plugs)

Anyhow.....

The misfire went away.

This car has fooled me a few times. Sometimes I *think* I've solved a problem but then it returns. However, I changed plugs 2-3 weeks ago and the misfire is still gone.

I have no concrete explanation. As I said, the "old" plugs looked perfect and over the years I personally have never experienced a problem with one brand of sparkplugs over another.

I am speculating (and that's all it is) that some sparkplugs might not be compatible with my replacement coils (another sore subject). This stretches my thinking a bit but I have no other explanation at this time.

Take all this purely on a "FWIW" basis. But, trying a different set of plugs will cost only $12.00 and take perhaps 20 minutes.

Cheers
DD

 

I am very strongly leaning towards TPS or EGR. More TPS. When mine was out it started with your symptoms and eventually escalated to "blacking out" momentarily at highway speeds. Like someone just turned the switch on an of

 

Okay, 93 greenconv, I will keep trying to find the problem and post it if I do. I am not sure my '96 has the idle bypass valve but will have a look.
RagJag

 

Doug, I had the problem and installed a new set of Champions. Did not change anything.
I don't know what the MAF does exactly but the IAC regulates intake air at idle. This engine will run with either unplugged. I suppose I could try a set of NGK plugs.
RagJag

 

Mark, You said your engine would completely cut out 'when it was out'. Did you ever find the cause??
RagJag

 

I was referring to the aTPS. When it started goin out the car would do what yours is doing now. That escalated to it cutting of at 70mph. Every time I would test it as prescribed it would come up as good. I changed it on a hunch and I was right, never had the same problem again.

 

I don't want to get too enthusiastic but I drove the Jag out into the city today and it didn't miss or die as it was doing. I installed the new Idle Air Valve a couple of days ago but hadn't driven it since. I have hope that was the fix I needed but am somewhat skeptical. We will see if it keeps running well. I will report back next week.
RagJag

 

I was looking on EBAY last night and I see the TPS is quite pricey. $350-500. I will get one if the problem starts again.
RagJag