well, I change the throttle body today . was actually worse . went back to the old one . seems as the tps wasnt reading . anyway, did find the egr ports extremely dirty in the intake. cleaned it up thinking ""I found it " . nope . same issues. idle just sucks when it drops below 1000rpm . still get the 24% trim 1 and -24% trim2 . however, if I give it some gas past the 1000 rpm they even out . also, if I remove the vacuum caps on the intake one side at a time I notice the trims changing . so, I have to conclude the sensors are working . can one of the sensors just be out of spec not reading in the low rpm range ? this is beyond frustrating . why cant there just be a code (like on a toyota) that says bank 1 bank 2 out of range . anyone got some next advise ? thankx

 

I have experienced several troubles on mine and my friends', so I will write down all of them other than the parts you have dealt with.
There might be an answer in them somehow.


1. ICV (idle control valve)
Once this goes bad, cleaning would done nothing. you have to exchange this. Don't exchange throttle body assy, just change this.

2. linear switch of the shift control
Sometimes the linear switch by the shift control goes bad. When this goes bad, the ECU can't pick up the information of which gear transmission is in. ECU reduce the fuel when it is in P, and it increase the fuel when it is D or R. So this sensor could causes the fuel richness problem.
If you have a problem with the shift gate when starting the engine, I mean sometimes the shift doesn't sit correctly in P and you can't start the engine, this is highly possible.


3. O2 sensor
at least most O2 sensors goes bad after 100000km drive, you could change these to the new ones. These are expendable parts, you have to change them someday.


4. Coolant temp sensor
Of course this is really essential to decide the fuel trim. This is a cheap part you could change with a new one immediately.


You mentioned you have high idle when you stomp the brake. As you know the brake servo needs negative pressure and it is taken from the intake manifold. So this could cause an idling problem. You could check the brake servo pipe. I am not sure about this, though.

 

[QUOTE=
2. linear switch of the shift control
Sometimes the linear switch by the shift control goes bad. When this goes bad, the ECU can't pick up the information of which gear transmission is in. ECU reduce the fuel when it is in P, and it increase the fuel when it is D or R. So this sensor could causes the fuel richness problem.
If you have a problem with the shift gate when starting the engine, I mean sometimes the shift doesn't sit correctly in P and you can't start the engine, this is highly possible.
[/QUOTE]

I think I have this problem on my xjr6 sometimes it doesn't start properly when I have it parked. I would have to shake or wiggle my J-gate in order to start it and it's starting to bother me at times. Is this problem an easy/accessible fix?

 

Fairly easy, yes. After removing the wood panel you'll see the linear switch on the right side of the gearshift assembly. The two hold-down screws are a little difficult to get a screwdriver on...but you can do it. Loosen the screws and slide the switch fore or aft to adjust. You want to make sure the "P" on the shift indicator glows red when the gearshift is in "Park".

I replaced the posi-drive screws with hex-head screws while I was at it, to ease the job if it ever needs to be done again.

Cheers
DD

 

Jaglips:
Have you checked for a cracked exhaust manifold? Air can be entrained into the exhaust stream causing the sort of thing you are experiencing. And it is the post cat O2s on this car that do the primary control, so you might be on to something with your swapping. You did get the right sensor hooked to the right cable, right?

 

ok . heres where Im at now . I checked out all 4 o2 sensors with some deductive reasoning . I figured out that the pre cat ones dont make any difference plugged in or not for my issue . not do they seem to effect any of the st fuel readings. I did learn the back o2 sensors after cat do make changes. if I unplug one, the idle smooths out and goes up . plug it back in and crap idle. do the same with the other one and same thing . however, if both unplugged, the car idles smooth but to high . trims both read 24.2 .. now if i plug one in I get the goofy readings of 24.2 and -25 between the banks . if I flip the sensors around (swap the banks ) then the goofy readings flip around . so , I can not imagine 1/2 the engine is running lean and 1/2 rich . seems to me somehow one or both the sensors are an issue .I do not think the water temp is bad as it reads correctly . idel control Im not sure but I would imagine that it would not cause 1 sensor to read rich and the other lean . to me it seems either both rich or both lean if in fact the idel air valve is bad. off course it could be bad and Ill get to that once I sort out these o2 readings.throttle body was clean inside . egr was nasty .also, when I changed the spark plugs last week, the old ones all looked good as far as burning goes. sfiter jgate ? well . that does make sense . however I dont feel thats the problem in my case . the mapping of the fuel changes when in drive so I assume its working .when in park and nuetral, idle goes up past 1000 rpm .however, prob a good idea to look into the jgate as sometimes it gets stuck and dont want to go into R . jammed . play with it and it clicks and goes . I must say I have learned quite a bit about this car so far .so, at this point Im thinking perhaps grabbing a new pair of rear o2 sensors and see what happens . fingers crossed . thankx .

 

yea, the brake servo Ill check . strange as this symptom was only sometimes .going to check anyway .

 

yea, going to check the brake servo anyway . strange thing is that it only did it sometimes .

 

Ill get a better look at the manifold .dont think its cracked. engine bay is not loud. dont have that sound . learned the hard way about the rear o2s doing the primary control . Im fairly sure the cables are in the right spot . but if I swap em, the strange readings 24.2,-25 stfuel flip as well . lends me to think something with the sensors.

 

Well, I assume you know this, but just to remind you- If one sensor reads incorrectly low (or high) it will move the LTFT, which is the same for both banks to the opposit direction from the bad sensor. ie, one sensor reads incorrectly lean, moves LTFT to call for rich, which then causes other sensor to read rich, the original sensor still reading lean.
And you are right, you are getting great experience in am area of the car that has a lot of poor or incorrect information- Aren't you lucky! :-)

 

Check the manifolds anyway. BOTH mine were cracked and I never heard a thing.

Cheers
DD

 

so, I decided to order 2 new oxygen sensors (Rear) for the car . figure best to swap both and see what happens . I am alomst positive this is the case . plus, between the original and donor ecu I get the same readings so I dont see it being any type of program issue at this point .plugged into a navigator last night to clear a check engine for someone .not that anything is the same but I watched how the st's worked in that truck and sure enough they were around the 5 mark . have them unplugged now . check engine is on but aside from the idle a bit high, runs much better in drive or reverse . off course Ill be checking the manifolds during the swap as well . thankx .will post my findings as soon as Im done.

 

ok, so I got the new aftermarket sensors . pulled the old ones out and sure enough . wrong sensor !! way to big . so, in a bind with no options as I have to drive car home and such , I grabbed a couple of used ones (yea I know ) .. one I had to splice wires back in . the other just a swap . after a few seconds of warm up, I get normal st fuel readings on my scanner . idle is smooth in drive and reverse with sensors hooked up . still idles a little high but only ran it a few minutes. still idles lower than with out the sensors hooked up . so, I think I nailed it but to be 100%, Ill know on my way home from the shop here .so which sensor was bad ? no idea . perhaps both . who knows . Ill post the rest after the ride home . fingers crossed .thankx

 

ok, again .. so, I decided to put in the original ecu just to see what would happen . well, my idle dropped to like 700 in park and nuetral. stays fairly ok in drive and reverse .but, it still has a slight stumble while sitting there for a while . no way to time it. just does it when it feels like it . the readings on the original ecu's st fuels stay at 24.2 both banks . took it for a drive and watched them move, fairly similar to each other .idle is not crap as it was before but that stoopid stumble . now, the lt fuels are around 10.1 where as with the donor ecu they are like -98 .. nothing else changed. just swap ecus .so , I do feel I found an issue with the o2 sensors for sure as they dont read -24 and 24 now. however, one ecu idles low and the other high ? perhaps the suggestion of someone with a jag tool to reset calibration in the ecu is a must .my stock ecu says its updated to some version in 1997 . the donor has a sticker on it with something 493 yr 2002 . I believe this to be the final updated ecu . so, anyone have any insight on this one ??

 

Yes. I bet the TPS adaption procedure will fix the high idle condition. I doubt it will do anything to the stumble.

 

well, I let someone drive the car today ( the one who normally drives it) . guess it runs like crap . nothings changed, stumbles and shakes at a light . so, Im going back with the donor ecu as I drove it and aside from high idle, no driving issues . sure would be nice if someone other than a dealer had a scanner that would reset these values of tps,,o2 and whatever . perhaps a reset trick ??? anyone ???

 

Pay an independent specialist his minimum shop charge (usually 1 hour) to do the re-sequence and TPS adaption. Or drive it to Atlanta a buy me a six pack.

 

would be more than happy to find an shop but no luck .off course my x431 dont do nearly anything for jags. mercedes ,vw and bmw is no problem .any of the asian stuff no problem either. think I may have to go to the dealer .

 

Hello every one. I'm having the same rough idle problem with my xj6, I remove the throtle body and cleane it. Ive also replaced all 6 coils with original lucas coils that I ordered fro the uk. I only paid $41.45 plus shiping. However the rough idle is still there. I did grab my scaner today and noticed that the MAF sensor is only reading 0.01 lbs/m does anybody know what that reading should be in adle? I did discover a cracked oil cap gasket, but I will check it further.

 

Any codes? You say you have "the same rough idle". Do you have high idle rpms like this thread? What are your fuel trims doing?
Lots of things can cause rough idle. Lets see if we can narrow your down!