[QUOTE=aholbro1;366624]good deal. I will check this search out . I did check the coils in the dark but didnt find anything unusual . swapped several coils and same thing .Im suspecting the throttle body at this point . it does have something to do with idle control . perhaps sensors are working but not reading properly and thats the reason for no check engine . like if it idles to high(which some do ) you wont get a check engine . who knows .

 

These are all used parts, yes? I'm not sure that swapping in used parts is very conclusive....unless the parts are coming directly off a car that you know doesn't have the same issue yours is having.


I'll also opine that I don't think these idle problems are necessarily casued by a hard fault of a single component. I think they can easily be the result of slight degradation of multiple components: an iffy coil, a slightly clogged injector, a lazy O2 sensor, etc. Any one of these things alone might not make a difference but if you have a "stack up" of items that are not up-to-snuff they'll together conspire to give a rough idle.

Even a few weeks ago when I was fighting much more severe symptoms I had "working" coils, for instance. They just weren't working very well :-). They car *driove* great. Only at start-up and idle did the weak coils become apparent. Go figure.






Mine is usually the same way. And it often idles smoothly unless I'm stuck at a long traffic light. Generally, the longer it idles, the worse the idle gets.







That's pretty strange. I really can't explain that one off-hand. I'll have to put on my thinking cap...but it's Sunday!









Is the misfire gone or is the higher rpm just masking it?







Not sure about you but my next step is having the injectors professionally cleaned. It's just a guess on my part.

Cheers
DD

 

theres a fiddly bit on throttle body cleaning. Very small brass screws fixing the throttle-position sensor, I beleive. Motorcarman cautioned me about it. I'm going to take that on within the next few weeks, I reckon, but you may want to ask him the specifics of how to handle that bit. I believe he told me you have to heat them for successful removal...but of course you don't want to cook the sensor.

Good point, Doug. I remember someone posting here that they get their fuel adaptions cleared once/yr and anytime they replace a component directly involved, like plugs. Said it smooths things up and increases fuel mileage. If it is a stack-up of stuff, could be clearing the adaptions would resolve it for the time being? Of course, you need WDS/IDS for that...I changed out Champions for NGK Iridiums last week and so far, no issues. As far as I know..the Champions were original, i"m at 85k mi.

 

yes. used parts as I have many of them . the stuff im putting on is low mileage . like 40-50k . that is what I used for the crank sensor,fuel injectors,rail and regulator . coils I just have a stack of them .I think the misfire is masked by the higher rpm . but then again, maybe not . its very smooth at 1000 rpm .whats funny is that its not a constant misfire at the low rpm . it just comes and goes . like sitting at a light all is well then a miss and you think its going to die, then it just picks back up . the longer it idles the worse it gets .

 

this clearing of adaptions I will have to look into . not sure if my launch system will do this . I know about these things on vw's and bmws and I hate anything with a w ..didnt think that a 96 xj6 would have such items . interesting .perhaps after a throttle body swap and or cleaning that may be my last bet . I have swapped ecus and same thing still which lends me to believe its something else still .

 

ok. so here are the 02 trim readings

st ftrm1 24.2
lt -93.7
st ftrm2 -25
lt -93.7

so what I see strange here is 3 of the values are -'s ? is this normal ?
this was done with a handheld tester foot on brake in drive.

now, I noticed if I unplug the air control valve (top of throttle body) it makes no difference nor does the check eng light come on . you would think the car would run worse or at least a light would come on . Im starting to think the valve is faulty . that would explain the crappy idle as their job is to control idle . just like any other car .anyone ??thankx again for all the helpful tips. I have to figure this out . its driving me nuts .

 

The negative fuel trim values tell us that the ECU is trying to lean out the mixture to compensate for a real or perceived rich condition. Positive fuel trims, opposite.

If the mixture isn't actually rich then leaning the mixture could certainly cause a rough idle.

The short term fuel trims should normally be +/- 5%. You have one bank trying to go lean and the other trying to go rich. This will take some mulling :-).

The fuel trims typically max out at 25%, as I understand it. The "93.7" readings you have for LTFT are apparently erroneous communication with your scan tool....or so I've been told. My LTFTs have been anywhere from 40-100% over the years while the STFTs have been normal.

Not sure what to make of your idle air control valve operation. More mulling.

Cheers
DD

 

XJRGUY is your friend:

https://www.jaguarforums.com/forum/g...ed-quiz-49317/

 

well, I have given this some great thought . now, the trims read from the sensors before the cat or after ? I first tried to swap the sensors in the pre cat positions to see if the bank1 and bank2 readings would flip .same readings. then I flipped the after cat sensors and while the readings didnt flip, they became consistent with that 5 % range . idle was nice in park and drive. however, the idle was high in park . around 1300 rpm . not sure why .but in drive idle was 800 , smooth with good trim readings .perhaps one of these sensors is going ? I feel Im getting closer .

 

well, I read the write up on the fuel trims . knowing more of how they work now, I think it will help me find the issue . thankx for the link !!
is it possible the cam cover could be the culprit ? 145k,common problem and never changed . there has been oil in a couple of the spark plug holes .hmm. if its leaking air towards one of the banks , then that could perhaps cause the readings I was getting . still doesnt explain why I was getting good readings yesterday though . high idle could mean vac leak as well . got a spare throttle body Im going to clean and try just in case its the idle air valve . then again, if that was the case wouldnt both trims be off ?

 

>Oil in a couple of plug holes

Of course this could be the reason of the rough idle. Rather, you should have done this first. It often causes rough idle and engine stalling.

 

this was the case a while ago . when I swapped in the champion plugs it was dry . all plugs looked good to .in any event, I m going to have to fix the cam cover gasket .

 

Do a quick engine compression test to check for a "leaky valve head" especially on the cylinder that you found oil in the spark plug well.

 

jaglips:
Once you mentioned the high idle, and with the LTFT trims giving the apparently incorrect numbers as pointed out by Doug, I have to tell you about something I did not previously believe buit have found to be true. There are two procedures run with WDS and IDS that restored my LTFT numbers to more reasonable values, got my idle correct and allowed my XJ6 to completer the OBD drive cycle, That was "TPS adaptation" and "O2 Resequence".
If you have access to IDS or WDS I suggest you give it a try. An independent shop should run these for you at the minimum shop charge of about 1 hour or less.

 

this is good info . I wish my launch x431 did this . however, I can not even access the ecu .have to use cheap scanner. done this kind of stuff with mercedes ,vw and bmw before .

 

this crossed my mind as well . perhaps this should have just been done first .Ill have to give it a try and see what I get .

 

I do not know how oil in the spark plug well is related to compression. This engine has no connection between the well and any head seal.

 

I agree.

A compression test my not be a bad idea on GPs, though, if battling a persistant roughness/misfire type symptom. You might find out you have a dead hole.....

But that's not what I wanted to talk about.... :-) :-)

MY idle tremble problem has been fixed ! I was cleaning my trunk and decided to have a look at the battery cables just for the heck of it. Took 'em off, they looked OK, I cleaned 'em anyway. Reinstalled, tightened them extra tight and voilá, the engine is just purrin' like a tomcat in a dairy at idle.

I can't explain it but I'm not complaining.

In theory, as I understand it, none of the adaptives will reset by merely interupting power....so I don't think that's the case. Perhaps there was some minute voltage drop that every other system the car didn't notice but, for some reason, deeply offended engine management. I dunno.

Crossing my fingers that it lasts :-)

Cheers
DD

 

I've heard stories of bad batteries causing all kinds of strange symptoms with these cars.

 

well, I can most certainly clean battery cables . never know, perhaps I may find something there . dirty ground and or dirty 12v can cause issues . Im still going to do a comp test just for the sake of knowing about the health of the motor. I can tell you in my specialty or rotary engines, a well running motor with a rough idle can have a cracked seal internally . not blown but cracked and you will have a rough idle .however, its always rough not intermittent . thats what gets me stumped here. its not always . its like a skip or a hick up .I also found another throttle body, cleaned it up nice and going to see .