I'm new to the jag world and I'm having a couple of issues with the XJS I just bought. The car has 106K on it and is in decent condition.
3 things are bothering me.
(1) high idle. 1150 rpm after the new IACV.
(2) over 3mph the idle wants to surge even more and drive the car up to 2700 RPM. This goes away if you unplug the IACV.
(3) check engine light is on when the key is on and goes out when I start the engine. Registers wont set. If I unplug any of the sensors, IACV air temp sensor ect it DOES NOT set a MAL. (this really scares me)

I've read a lot of info on this site and sometime have trouble finding info specific for the 1995 and 1996 XJS 4.0. I need some specific help with these conditions on a 1996. I did purchase a IACV because I was sure it was not functioning correctly and upon installation of the new piece it does work differently. I even had a 600 RPM at idle for a day.

I have ordered a new AIR temp sensor, thermostat, and engine temp sensor.

I also plan to remove my O2 sensors, cleaning them up and verify I have the right plugs in the car.

Service history on the car going back 7 years suggests none of these items were touched.

Can anybody help?
Anybody close that I could sit down and talk with?

 

As an additional note, I did clean the throttle body.
I also stopped by the local Jag dealer and they said they could look at it but did not fill me with confidence that they had anybody who really knew the older cars.

 

You need someone that has the WDS program to reset your base idle adaptations. You can keep throwing parts at it, but there isn't another way out.


I have a ton of posts over my years here trying to extinguish that same problem. $150 at a Jag specialist and all the idle problems went away.


You aren't terribly far away from DC. There are two shops that specialize in Jags that can fix your problem.


Master Auto Service in Rockville, MD is excellent. They found and resolved a very strange tick my engine was having that the next person on my list could not diagnose. They don't have a PDU, but they have fixed my idle issues before.


Top Line in Springfield, VA has a working PDU! They're apparently a very busy shop, but if you call ahead and tell them what the deal is, perhaps they can hook you up to the PDU straightaway and fix your problem the same day. They are not the best at communication. They have a fascinating amount of old E-types and such in their shop.


I remember seeing a British shop somewhere in Harrisburg, PA. That's closer to you, but I know nothing about them.

 

Hitch, as for wanting someone to sit down and talk with; you have an XJS so I suggest a therapist.

 

Steve,

How true...and to think I sold a perfect Lexus SC400 to buy this. I do need help..or a PDU.

 

Vee,
My local Jaguar dealership refuted the existence of such a device (PDU). Can anyone recommend as location closer to Bucks county PA that has one and know how to use it?

 

You're not going to find a PDU closer to you, so let's focus in on a WDS.


Ditch the dealer and start calling british, or European car experts. They should at least know what you're talking about.


DC is a fun town. You can drive down here and make a weekend out of it! On the bright side, I've never needed a second reset. Seems to be something that happens only when you buy a car that either has sat for a long time, or when someone changes the IAC? I don't know what causes it, but once you resolve that, it'll get easier from there.


Never did like the SC400 body. You will never confuse the simple ownership of a Japanese car with this Jag.

 

So tonight on the advice of Anthony Abonano I took the throttle body off and really cleaned it well. To do this right you have to take it off. There was a ton of gunk on the back side of the throttle plate. Additionally there was built up gunk at the idle air control valve seat and connecting ports.

I also noticed that the mating surface between the manifold and the TB had a film on it, like a thin spray on gasket sealer. I cleaned the manifold and the TB. I also cleaned the mating surface for my new IACV.

I don't really know what I'm doing with an Ohms meter but I thought I'd check out what kind of readings I get since I had it out. With the TB up side down and the open face on the connector towards me I'm labeling the connector pins 1,2,3, right to left.

Between 1 & 2 .3 ohms between 1 & 3 .34 ohms between 2 & 3 .3 ohms. If I slowly open the throttle plate while on pins 1 & 3 ohms climbed to .59 ohms. Similar results between pins 2 & 3 and no change between pins 1 & 2. Not sure what this means since I have not seen anything to judge it by.

My original (date coded 11/96) IAC valve was installed with a metal ring and a gasket. The new one came with an O ring. I had originally installed the new IACV with the O ring. When I did this on my work bench though I noticed a gap between the IACV and the mating surface. I took off the O ring and installed it with just the metal ring and the gasket. I also used a little Permatex gasket sealer on the mating surface.

I took the EGR valve off and cleaned that up also and reinstalled it with a gasket and Permatex gasket sealer.

I actually had used 1500 wet dry sandpaper to finish cleaning the manifold and the TB. Put a little Never Seez on the bolts(used on all the bolts in this post) and put a thin film of gasket sealer on the TB. I'm just not happy with a lack of a gasket there. Tightened it down evenly and reconnected all the plumbing and electrical lines.

On fist start it ran a little high while the IACV tried to do its job. I forgot that if you leave the ignition on, engine off, for 7 seconds the IACV will close the gap in the TB. You may have to do this twice.

I turned the car off, left IACV settle down and started it again. The idle went right to 700 RPM and stayed there for about 30 seconds (watching the dash clock) and then it stated to creep up. It finally leveled off at 1100 RPM.

I started the car several times and the same events occurred...700 RPM and then after about 30 seconds it moved up to 1100 RPM.

It was nice to see 700 if only for a short time.

I know this is kinda drawn out but just trying to help the next guy.

Next on the agenda is a Thermostat and a new engine management temp sensor. For those that don't know the difference, on the thermostat housing there are two sensors. The one with a spade connector is for your temp gauge in the dash. The other one with the water proof connector and U clip is for the ECU. I'm replacing that ($30) because if you take it off when the car is running the RPM s will climb rapidly after about 10 seconds. I don't know if I have a problem with the temp sensor or not but the way it affects the ECU is critical.

I am also going to replace the upstream O2 sensors. I believe these are the most critical ones when it comes to engine performance and MPGs.

After this is all done I thing I'm going to meet up with Anthony who has the right software in NJ and get the throttle position sensor and O2 sensors recalibrated to the ECM.

I promise to let you all know how this effects the engine performance and my hunt for a low idle every step of the way.

 

Ok Today was a short day on the Jag..If you remember I cleaned the TB and installed the new IACV. Idle started at 700 RPM and moved to 1100 in about 30 seconds.

A friend of mine had a smoke machine to check for leaks so early AM we gave it a try. The new IACV was leaking at the seams. Spray it with carb cleaner and you could watch the fuel trim change. Now I know what the O ring on the IACV was for.

Also, I got some strange readings from my MAF sensor reading .9 - 21 g/s. Seems low.
Can anybody else confirm or refute this reading on their 4.0
I hope this doesn't mean I need a MAF ....

I'll keep you all posted.

 

Hitch,

I realize you've already taken the throttle body off and have performed the cleaning, but have you verified that the butterfly is set to .002" at rest?

It's plausible that the butterfly is not closing all the way to .002 and needs to be adjusted.

It's the only other thing I can add at this point. You'd need a feeler gauge to make sure of the spacing, but could be worth your time. I can't say I've ever done that before, but I've never resolved the problem without a computer!

 

My ongoing issue with the 1996 XJS 4.0 is that the computer will not set a mil light or put the ECU in a closed loop with monitored systems. It runs ok, idle still a little high but I can not get the car thru PA emmisions or even get an exemption because the ECU wont set.

If your 1996 XJS is running fine and you unplug an emissions controlled device, say the IACV or the MAF sensor you check engine light comes on right?
My check engine light does not come on.
It does come on when the ignition is on before I start the engine so it is not a bulb.

Has anybody experienced this?

I'd love to hook it up to a PDU but I cant drive the car anywhere. No PA inspection

 

Vee,
With the butterfly closed it actually held the carb cleaner in like a cup. I guess that means I do not have .002 but i also don't have a low idle issue. You would happen to have a spare ECU would you?
Bob

 

I'm afraid you'd be trading in one issue for another. My other ECU will not go into closed loop. It will not read a negative value for the oxygen sensors.

If I ever find someone capable of fixing it, I will have it reconditioned. Until then, I can't help you.

I'm not sure fuel would leak out of a gap only 2 thousandths wide. That's pretty damn slim. You could get a feeler gauge in there to check. Could be the answer? I have to admit, I've never done it myself, so it could be worth a try?

 

Thanks Vee. I think I'm getting my waiver tomorrow so at least i'll be able to run it a little more. I read something about it not going into closed loop in park or neutral unless you put a jumper in a plug in the trunk. Is that the case for our cars or something older?

 

AOCP, RON, BOQ FUBAR it's like been back in the military. Could I respectfully request that the first time you are going to use abbreviation that you start it out like this:
AIRCRAFT OUT OF COMMISSION PARTS (AOCP) From then on use the abbreviation. Remember you are talking to people all over the world at many different skill levels and languages.

 

ECU engine control unit or in British terms Everything Could be Upset. Sorry there Afterburner.

 

So I thought I was getting my waiver today. Wrong....my mechanic got an appointment with the regional emission referee. Not optional in this case He said he was familiar with this car and its history of problems and wanted to look at the car personally. I'm going to take the positive position on this . I'm hoping that this means I'm get some free top notch diagnostics help....We will see......

By the way, We did pull the ECU (ok Afterburner?) and it was replaced in 2009 with a new Lucas unit. Discharged the battery, ECU looked clean with no evidence of moisture damage.

I'll keep you posted

 

New ECU by Lucas?

How was it new? I'm a bit confused. How do you know the part was. Ew? I can't believe they were still selling those things new in 2009?

 

The tag on the Ecu unit which read Lucas showed and install date of January 2009.

 

Hitch, I'm also in PA, got classic plates for my '94, emissions test is not required with classic plates.