Recently I've developed a fairly pronounced idle tremble/misfire. It began as an intermittent fault and is now constant.

On top of that, and possibly related....or possibly not.....three days ago I experienced some severe engine misfiring where the engine would bog down and shake violently...barely stay running in fact....as the throttle was opened from idle. After passing through this violent shaking the engine became totally smooth at about 1200 rpm.

This behavior went on for 20 minutes ....whenever the throttle was opened from idle ....and then disappeared entirely. The car has been fine for 3 days...except for the previously mentioned idle tremble, which remained.

Some info from yesterday:
1) All four oxygen sensors are virtually fixed at .045v from idle rpm to 1200 rpm. At 1200 rpm they vary normally from .045 to 1.25v

2) STFT both banks at idle seems virtually fixed at +24.2 until 1200 rpm is reached at which point it drops to +3 to +6. If I understand correctly this tells me that fuel is being added to compensate for a real or "imagined" lean condition

3) I have a code P0430, cat convertor efficiency. I should mention that I've been chasing P0430 on-and-off for years. The car has always run well even with the fault present. I've replaced exhaust manifolds, checked for air leaks, etc. I had become to think of it as a phantom code. Now it might indicate a genuine problem.

4) TheTPS percentage seems to increase smoothly as the throttle is opened and rpm passes thru to 1200. There doesn't seem to a dead spot where it drops out. I'm not sure if that confirms a "good" TPS or not. (I say "seems" because it's a little hard to open the throttle slowly and delicately enough to observe tenth-by-tenth increases in the percentage.)

The car runs great on the road. No misfires, no roughness, no power loss, fuel economy has not suffered.

Any thoughts on this problem?


Thanks
DD

 

How do the coils look?

 

unfortunatly the x300 his hard to throw misifre codes, mine just did the same thing but was flashing the CEL for cat damaging and popped a 301. fortunatly it just had alittle water from me cleaning the engine a couple days before. But I did find that partsgeek.com had new coils for about $57 each vs $300ea from Jag. I would pull out the coils and look for crossfires to the cam cover. Theyr notorious for arcing and the result is very damaged and arced up cam covers. The offending holes useally have black powder in them and distorted metal

 

Jack and Brutal, given the spotty history of these coils I was thinking along the same lines. I just got in from checking the coils and, whaddya know, two replies regarding coils :-).

Anyhow....No signs of arcing, no black residue, etc.

I checked the primary resistance on all of them. Spec is .75 ohm. I have three at 1.0 ohm, two at 1.2 ohm, and one a .9 ohm. I was hoping to find one that was wayyy out-of-range.

Well, anyhow, I'll replace the two that are most out-of-spec and see if anything changes. <shrug>

I've learned to accept that some failures don't make sense but if it IS a coil problem I have to wonder why I don't get any misfires under load.

The reluctance of OBD on these cars to set a code is.... interesting.

Thanks for the comments and suggestions, gents.

Cheers
DD

 

Doug,

Four of my six coils were lighting up in the dark and sending spark back into the ignition system. They weren't even cracked or worn. They were brand new as a matter of fact. The way they showed damage was the sealant in the top bubbled up. The engine would shudder and fail altogether and my car never set a misfire code. Not even the generic one.

 

THIS IS WHY I LIKE A SCANNER THAT CAN SHOW MISFIRE COUNTS(NUMBER OF TIMES A CYLINDER HAS MISIFRED) A COUNTER SHOWS THOUSANDS OF MISFIRES THAT YOU SURE CAN FEEL WHEN AT IDLE AND NO MISIFRE CODES PENDING OR OTHERWISE. MAYBE THE THRESHOLD IS 10K +
BECAUSE IVE NEVER SEEN ANY OVER 10K WITHOUT A CEL. BUT IVE SEEN MANY 8-9k PER CYLINDER. AND UNFORTUNATLY OUR GENRAD JAGUAR SCANNER THATS NO LONGER MADE THAT PULLED COUNTS DISAPPEARED A MONTH AGO
MIFIRES AT IDLE ARE THE MOST COMMON AND HARDEST CONDITIONS TO FIRE UNDER FOLLOWED CLOSELY BY FULL THROTTLE UNDER LOADED CONDITIONS. PLUS AT IDLE YOU DEFINTLY FEEL AT SUCH SLOW ENGINE SPEED, NOT REALLY AT HIGHER RPM CAUSE IT HAPPENS TO FAST TO FEEL EASILY

 

Hi gang,

I replaced the two coils that showed the highest resistance, car runs great, seems to be fixed. I'll report back if the problem rears it head again but I'm "cautiously optimistic" that the coils did the trick.

Cheers and thanks
DD

 

I believe the coils are a root of a plethora of evils when it comes to this car. Whatever tolerances were used to construct the cheap HamburgTechnic coils (Chinese Made) did not give them a life over 7 months. They were firing both forwards into the sparkplug and backwards into the ignition system.

Surely to goodness someone has designed, or COULD design a coil that has built in safeguards against firing backwards and against cracking at engine temperature. In short, can't someone make something that works where it is supposed to when it is supposed to???

 

Jack, aftermarket coils indeed seem to get mixed reviews. I myself took a gamble with Beck Arnley coils....about 1/3 the price of the Lucas OEM. The coils themselves have no markings of any kind other than "PEC". Not sure what that means but it all sounds very "Brand X" to me. Fingers crossed as to how long they last.

Knowing what you're getting can be difficult with the way parts are merchandized: the very same part, be it good or bad, thrown into different boxes with different names. One can only hope that outfits with a reputation to protect (Beck Arnley, for example) would not knowingly sell unadulterated junk.

I can be a tough call when the price gap is so large and you're not even 100% sure replacement will solve the problem.

Cheers
DD