Hello,

After throwing $1,300 dollars at the high idle issue I've been dealing with... new throttle body, vacuum hoses (that did not solve it). The mechanic noticed my alternator was creating way too much electricity (forgive me for not phrasing this in technical terms) anyway - apparently it fried my ECU. Now since this is another possible cause for the idle issue...The shop is asking me $1,100 for an ECU with a guarantee. Is there another place to get an ECU with a guarantee at a lower price? I haven't been able to drive this car since buying it because I can't get it smogged ...so needless to say, I don't want to spend this much if there is another option.

 

The high idle likely just needed the TPS to be reset. Only someone with Jaguar diagnostic equipment can do this.

There may be other reasons, such as vacuum leak, bad MAF or bad IACV, but a fried ECU has not been reported here in the past. Not saying it’s not plausible, just rather unlikely.

Im not sure where Pacific Grove is exactly, but someone should be able to help you find someone that can solve your problem.

 

Vee, I appreciate the advice about trying a TPS reset, I will need to double check that my mechanic has done that already. I feel as if he had done that but I am not certain. The reason for my post is to purchase an ECU from a good source that is guaranteed to be working, since the ECU seemed to have burned out after having the over active alternator. I currently cannot drive the vehicle (high idle or not) without the ECU.

Thank you

Michael

 

I'm a bit confused, usually electrical items have no guarantee once they have been installed. If the alternator regulator is bad that will allow the voltage to rise too high, but it doesn't usually fry the ECU. Unless that is fixed, a second ECU will fail as well.

On these cars high idle is usually cured by doing a throttle adaptation, you need dealer level software to do that. There are DIY ways to obtain the software, but it isn't always cheap - you need a special cable between your laptop and the car.

I'll have to look at the wiring diagrams, and see if the ECU from an XJ6 will also work. The engines and transmissions are the same for 1996.

 

Unless this shop is someone you really believe and trust, I would get it out of there.

ECUs for these models are not easy to come by, so they command a premium. I would make sure you take the old ECU with you when you're done. Perhaps there's a way to salvage that one.

I suspect he doesn't know what he's doing, but that's neither here nor there at this point. I guess have him replace the alternator, and the ECU and just take it as is, high idle and all. I don't believe the mechanic will be able to fix your car....but that's just a suspicion.

I'm sorry you are in this position.

I believe the ECU part is LHE1410. You’ll see it’s rather difficult to source, however, the XJ6 use a similar ECU LHE1410 that should work, and cost a lot less. You may have some dashboard security light that won’t shut off, or
something like that, but it should function identically. It might be worth a shot.

Lastly, make sure whatever ECU you get, you know the VIN number of the car you pulled it from. I believe all of the Jag Diagnostic equipment ask for it before it can interrogate the ECU. I don’t know if Ive ever tried to put in a bad number to see what happens.

 

Thank you so much for the advice Jagboi and Vee. This allows me to feel less helpless in my search. I have owned the vehicle for 3 months now and haven't been able to enjoy it yet. I will try and get it running so I can get it out of the current mechanics care. I have very limited options here for help with the vehilce (which is hard to believe). The local dealer won't even look at it or discuss it.

 

If I were you I'd get a 1995. I saw picts of the car in your profile so I know this wont be easy. 1995's are OBD1 and far are easier to get through CA state inspections. This may end up being an on-going issue for a 1996 car and may impact your enjoyment of the car long term. 1996 was first year of OBD2 and your car's ECM will need to meet "readiness" to pass the state inspections. That means everything will need to be just right engine sensor wise and the lack of qualified personnel and equipment to make that happen will be a constant battle.

Other options like retrograding to a 1995 ECM and getting it registered in another state may be ideal.

 

I'm realizing that you are correct icsamerica

 

For you high idle:
Is your mechanic a Jaguar guy with original Jaguar diagnostic tools OR using Autologic? Those are the only tools that I know of are able to do the TPS setup.
I might know a company in San Francisco who has got the correct tools for it if that helps.

But we need to know if the TPS setup has been done correct with the above diagnostic tools.

 

Just tossing out - any vacuum leak downsteam of the MAF sensor witt give you a high idle, not just confined to hoses. There is a base adjustment screw on the throttle body, the idle air adjustment can take it above this baseline, but not below it. Cruise control, or, more obviously, throttle cable hanging up?

To me, really unlikely that overvoltage would fry the ecm, but leave the car runnable. Might need to ask him if the ECM is pulsing the idle air control motor? I do have an ECM sitting on my desk, LHE 1410, built as am AF, last upgrade was to "AL" in '03. I bought as a spare, have not used it, but certainly would not guarantee it - seller did not guarantee to me, either. Think I paid about $375 for it. ECM's for these are (at least to me) not plug and play, it will likely run poorly if just installed blindly, until it has enough drive cycles on it to adapt to you engine.It will have whatever oxygen sensor port assignment the last user had, it will have the long term fuel corrections from the last engine, etc. As far as I know, and I am not 100% on this, the GEMS 6 ECM's had a habit of "drifting" on fuel trims, with no limits to haul them back in until they reach a "Hard" stop at about 25% correction.

Asd the others have said, good guy with real live Jaguar software can handle this, but "ECM fried" doesn't carry much credibility.

Good luck with your car, hope it works out, but you might need either more specific answers from your mechanic, or a different one.. A guy with generic OBD scanner is not likely to be able to help you.

Best,

Mike

 

Mike,

I really appreciate the advice. I have come to realize that my overly confident mechanic (who works on $1,000,000 cars and charges a lot) is terrible. I did get a 1996 ECU from another member here and I plan to take my car to a new mechanic in Campbell, CA called British/European. It's been a frustrating and expensive journey so far with this XJS, but guys like you have really helped and made me feel like there is a solution other than selling the vehicle.

 

You will need to do the throttle adaption with the new ECU unless you get lucky. How it works is once the throttle is properly closed, hard against the stop, the throttle position sensor reports a voltage. When you do the throttle adaption, this tells the ECU what voltage is closed throttle. Once closed throttle is achieved, then the ECU will activate the idle air control motor to bring the idle speed to the target RPM.

The closed throttle voltage will be unique for each car, so the chances of whatever is stored in the spare ECU being right are not great. If the stored voltage is higher than what your car produces, you'll be fine, so it might work.

Previous generations used a slotted throttle position switch that had to be adjusted, the newer one is done with a diagnostic computer.

 

The question is: does he has the original Jaguar
Jaguar software or Jaguar Autologic, otherwise he can have the best intentions but he will not be able to do it right. Like above mentioned, the TPS needs to be set and the O2 sensors need to be orientated to the car!

Edit: looked on there website and they uses Autologic! Please ask user Vee, to be sure Autologic is capable to do these two functions, I thought it would but just to be sure.

 

I have no personal experience with Autologic. I have been told it can be used to reset the TPS, but I guess we're finally gonna get a solid confirmation?

As far as what Fast40driver told you, its not entirely accurate.

1. SOME throttle bodies have an idle adjustment screw. Many do not. My 1996 does not. None of the throttle bodies I've seen on eBay the screw. I'm not sure how to delineate which MYs or models for that matter, have this screw. He is correct that any vaccum leak between the engine and the MAF can throw off idle. I had an intermittent idle issue which was caused by a failing intake manifold gasket. Apparently difficult for shops to diagnose, but I suspect if the leak was large enough to throw off idle all the time, your shop would have discovered that.

2. The problem he's experienced with the drifting idle is a known issue with the 1995 MY XJS ECUs. (and possibly the x300) The 1996 does not have this problem. Basically the long term trims seem to drift out to where the car seems to drive well, but the numbers would indicate there's something wrong. Basically the LTFT numbers for the 1995 MY are not useful to investigate problems, unless you have something that can reset those trims, which, I believe, only the PDU can do.

3. The ECUs for same MY ECUs should be plug and play with the exception of the TPS. That stays locked in until reset by something designed to reset the value. Every car has a base idle value, somewhere around 0.60v. A slight voltage shift to lets say 0.62 would throw off your idle. That happens with age, and the car is apparently designed to learn over time as the ECU gets older. (at least thats what the Jag manuals claim) In any case, if you can adjust the TPS on your car so when it rests at idle, it matches the voltage the ECU has recorded, everyone will be happy. If you don't have a machine that can reset the ECU's TPS base idle voltage setting, that's about the best you can do.

If this new shop has the software to do it, they can fix you up in a matter of minutes.

As I've mentioned before, if you can get your hands on a VCM, Mongoose, or mongoose clone, it could resolve this problem for you. The clones, while not reliable, could be a useful rainy day, one use only fix. I don't think they cost more than an hour's worth of labor at a shop....

 

I may dig in and see if I have a Mongoose stored somewhere? Perhaps there's value in making it available to people for the TPS reset?

I guess I would need to send the Mongoose, a laptop, the charger for the laptop and instructions?

 

I believe the AJ6 engines have the adjustment, the AJ16 does not.

 

Makes sense. I have talked to, or at least read old posts from AJ16 owners here who had the screw. I have to assume Jaguar was exhausting their supply before moving on to the new design.

 

If it can be done with SDD (which includes IDS) than your address British/European should be fine as I saw they have SDD as well. My experience with SDD and an early XK8 was that it was to old to handle.

Further I found this in an manual:

As you don't know if your car or the car where your new ECU came from still had the original O2 sensor orientation it needs to be done.
But I have got faith in your new address. Maybe you can point/ask if they can do TPS setup and O2 sensor orientation before you have got a high invoice for diagnostics.

Personally I have helped a person with an XJ40 and transmission light, he had spend 3000 euro's on it but nobody was able to read the code from the TCM, with the correct diagnostic tool it took me 5 minutes to diagnose and a 100 euro sensor his problem was fixed! Now I am in contact with somebody with a DB7 with similar problem and same amount of money already spend but wasn't able to read the TCM. What I am trying to say: the correct tools are key.

 

Wondering if you have solved your problems and passed your emissions test?

 

Thank you for asking Gijzzy. The short story is things actually got worse...
After getting the car back from the shop here in Monterey (after nearly 3K spent) mostly on chasing the high idle problem and also swapping the alternator. I was running a temporary ECU borrowed from the shop that is not correct for the vehicle (it is a 1997 XJ6 ECU I believe- this was information given to me from another member here). The car was running very well and the idle was right where it should be. I drove the car home and parked it in the garage. A few days later it wouldn't start. The battery was completely drained. I trickle charged the the battery (which is only 2 years old) hooked it back up... and then nothing. Not even an attempt to crank. Just nothing. So...I had AAA tow the car to "British/European" in Campbell California based on a recommendation from another member here in the bay area. They have had the car for 2 days now, and they said they are "scratching their heads a bit" to diagnose it's current condition. After some heavy losses in the stock market and not being able even drive yet after 4 months and now this...I am very discouraged.