Hi guys, I have "successfully solved" this (laughing at self) annoying issue, oh aboutv4 times in the last few weeks.

Here's what happens. Originally rough idle, especially when cold, step on gas drive away it feels like a vibration through the steering wheel. Actually this might describe it better: you know how if you leave a car sit on a low pressure tire for a few months, your going to get a flat spot on the tire? It'll take a few miles for that thump feeling to go away. Now imagine what a tire with 5 or 6 of these flat spots would feel like. That's what this feels like.

The frustration is that this comes and goes. Don't laugh but every attempt to rid it: clean throttle body, triple check sir intake is sealed, new plugs makes me think the problem is gone (yea!!) - for a few days then its back!

This morning I changed the fuel filter because it was time, and frankly I hoped it would help. Once again - test drive, I was smiling. Smooth acceleration, no issue. Beautiful day, the dog and I enjoyed a 30 mile cruise.

5 hours later I just took the car for an errand - its back!

Now I should mention that it is way more subdued than what I felt 2 months ago. In fact idle is fine, I really only notice this when accelerating with mild throttle. The just perceptible machine gun like staccato (vibration?) Feeling comes out.

I should note: check engine lights never come on.
No codes are stored.

Overall the issue is diminished in intensity from when it started, wonder if its because of the work I mentioned.

Any ideas about how to track this down? I've read stories about how failing coils can show under acceleration, but for what I've read bad coils or misfires always leave codes right?

I'd sure appreciate any thoughts, ideas, and suggestions you might have.

Thanks!

John

 

When you compare it to the feeling of having flat spots on the tires makes me think of the hydraulic engine mounts. That was how the ride felt for me when the mounts where due. Only in certain ranges of rpm, as I remember it between 900 and 2100 rpm. And worsening over time

After having replaced the mounts; completely gone

 

Thanks Higgins. They are not that old, but easy enough to check. I'll look later 2day.

John

 

Mounts are good.

 

When you took the old plugs out, you didn't see anything abnormal right? Also, no residue on the threads and no oil in the spark plug wells?

 

Also, when you checked that the air intake is sealed, what components did you check and how did you check them? I wonder if there still might be a leak somewhere (e.g. intake manifold), which may have caused your fuel trims to be off which may have had your car running rich and accelerating your old spark plug deterioration.

 

Oil in wells, yes. Its there in a few of them.

If that leads you to misfire, wouldn't that cause a code?

How to check? Visually. Taped up a crack in the intake tube.

 

Hm. Yeah, I don't know. The spark plug seals, so technically it's not like the oil should be getting into the cylinder or fouling the plug. However, if it's bad enough, I could imagine it might inhibit the coil from sparking to the plug with full efficiency (even though that's supposed to seal, too). It's a cheap fix, so probably worth doing regardless. Are the coil boots all in good shape? A defect might cause arcing and detonation, although given that the issue went away briefly when you changed plugs, I'm inclined to think the boots are not a problem (otherwise the issue would never have gone away).

Do you have a scanner to read fuel trims with? I am curious if they are out of whack.

 

Add a can of BG44K to a full tank of gas and see what takes place.

Gus
JagRepair.com - Jaguar Repair Information Resource

 

No codes ? Agree with above ^^^. Fuel issue, injectors or, (God forbid) fuel pump. You could try cleaning the MAF. It might not help, but it's cheap and easy. One other possibility is clogged cats. Not very common, but I did have that problem once (on another car).

 

Could a failing fuel pump do this?

Just spent an hour+ reading the fuel trims. Kind of learning as I go here.

I have 8 readings available. Short term banks, short term bank 2, long term bank 1, long term bank 2, short term bank 1 sensor 1, short term bank 1 sensor 1, short term bank 2 sensor 1, short term bank 2 sensor 2.

During my reading, understanding all this I read the long string of posts about this on here. I couldn't decipher any reliable indications from any of the 4 readings that don't include the word sensor.

After reading some posts I tried again. This time at idle. The long term readings were close to each other (bank 1 and 2). Short term were unstable and no trend identified. I noticed there might be a trend short term when sensors are read.

Warmed up car, cruise control on, rpms about 1200. Intersting. Both bank's #2 sensors were reading similar positive numbers (4 or 5% from memory), though sensor #1 on bank 1 and 2 were stuck in negative number territory. (Negative 2 or 3)

I'm not 100% sure about the exact numbers, have to check tomorrow, I am certainly still directionally accurate though.

I just wanted to share findings so far in case something is obvious or obviously missing :-).

I appreciate all the help.

John

 

See if this helps you better understand fuel trims JagRepair.com - Jaguar Repair Information Resource
Did you try the BG44K yet?

 

Thanks Gus. I'm hunting for BG44K around here.

John

 

Found it! Simple as checking Amazon, Duh. . .
J

 

Most dealerships and quality garages have BG44K but Amazon will work..

 

Have the super rough idle/full dash lights problem. Interesting reading about checking fuel trims. I haven't been able to pull codes since I bought the car 2 months ago. Used good readers which powered up, tried all the standard fixes suggested in here. Would buying Jag SSD or a more expensive meter (which mentions Jag compatibility) solve the problem? Indie had no problem pulling codes. That's the only reason my car is at his shop.

Odd that disconnecting ABS (C1095, module defective) got the car to idle perfectly smoothly. Installed a rebuilt (Module Masters in ID) and idle problem is back again. All coils recently replaced by seller. When the car runs, it's great. Too bad this doesn't happen more often. Codes are PO300 (random misfire), PO305 (#5), PO308 (#8). Indie thinks secondary circuits (to coils) aren't triggering correctly and wants to replace the ECU. Comments appreciated.

 

I have heard stories of cheapo coils being bad out of the box, and also stories of bad ECUs showing similar behavior on the earlier model years (97 - 99). Maybe someone with more direct experience will chime in.

 

Hi. I had exactly the same problem. No codes!! It turned out to be a failing coil. When this coil was changed the problem disappeared.
\jan

 

Thanks. No codes meant working on the car has been a lot harder (and more expensive) than planned. Be interesting to see if I get codes w/ the replacement ECU (which hopefully solves the misfire/rough idle problems).
My indie did pull codes using Jag SSD.

Anyone had experience w/ Precision ECU? Rebuilt ECU is 315. One year warranty.

 

Jan, this may be obvious but how did you find the defective coil without codes?

John