Trying to resolve slight rough idle, found another problem!

So my 97 xk8 has a rough idle. The plugs and coils seem fine, I have cleaned the mag sensor, and I have sprayed around with carb cleaner looking for a vacuum leak with no change. I was looking around the throttle body and on the left side I noticed some cut wires. I’m trying to figure out what they go to, but am hitting a wall. They are orange and black. Not sure what it is, but maybe a cause for the idle?

On my car there is a two pin plug low down and on the back side of the throttle body. It has an orange and black wire going to it, same as yours. The only thing that I can think this feeds is the throttle motor but the wiring diagram shows these wires as being red and green. The wiring diagrams have been known to be wrong, especially about cable colours. I can’t see any other connector on my throttle body with only two wires. My car is the same age as yours.

Have a feel down the back of your throttle body and see if you can feel this connector. The two wires disappear into their own bit of the harness in a convoluted plastic outer.

That is a possibility. I was also seeing red and green mentioned. I could see where the wires went, but wasn’t sure what they were for, or why they would’ve been cut in the first place. Of course I did also remember, when I saw it, that there is a 4 wire connector on the right side (possibly tps) that was cut and spliced at some point in its life smh

Different car being a ‘99 XJR but I have the same slightly rough idle, I’m just living with it, a bit annoying as my S11 4.2 idles steady as a rock albeit in neutral it’s a tad high at 1250-1300rpm but in drive or reverse its at 650 :slight_smile:

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That’s kinda what I have been doing. Living with it. I just figured I’d look into it and see if maybe it was something “simple”

I have replaced all the coils and plugs to no avail so it is what it is.

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so I finally decided to pull my throttle body today and look around. I’m not sure what the connector from the first post was, but as you can see, it goes nowhere! I also pulled on the spliced wires at my tps and one of them broke easily. I think all but 2 strands were broken. Another one broke fairly easily too. I cut off the connectors and the wires all had corrosion at the tips. I cleaned them up and then thought to look at my spare throttle body. My spare had a connector on it with about 3 inches of wire on it, so I decided to use that one to solder and shrink tube then electrical taped over top. I decided to try my spare tb and put it all together again. I started the car and it idled high and immediately got an engine fault and nothing happened when I pressed the pedal :tired_face:. . I thought maybe I had to let the computer relearn the throttle body since I had swapped it, so I started to pull everything out of the trunk and got to the battery. I looked at it and thought “double check connectors first”. I walked up front and sure enough I hadn’t connected the throttle sensor on the left. I connected it and started it again. Idled well and rpm increased with pedal! Yay! I took it for a drive and it seems smoother, not perfect, but definitely better! Ok so I just realized that the tps is probably the sensor on the left. What’s the 4 wire one on the right side?

Because of Jaguar’s anxiety over safety, XK8 throttle bodies are more complicated than those for totally ‘drive by wire’ systems such as is used in S Type.

So, in addition to the normal TPS (four wires) there are the two cables for the throttle motor and five for the pedal position and mechanical guard sensors. It’s too cold and wet to go outside to look but it’s possible the connector for these may only appear to have four wires because the PPS could be two wires in a single screened sheath and this may be the one to which you refer.

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Hmmm I have a 4 wire and a 2 wire on the right, and a 5 wire on the left. The one in the other pictures is at the bottom of the tb on a bracket, the wires don’t go through the connector though. My spare tb had the bracket, but it didn’t look like it ever had the connector

So, you’ve got all the right connectors on one of them. There is a note on the wiring diagram that early cars had a different configuration. The change point is 003300. Maybe, the other one is from an early car.
The two wires that are cut, are they from the throttle motor and was the car running with them cut?

Mines a 7/96 car number 001439. The cut wires on the left literally only go to the connector, with no wires coming out of the other side of the connector. I have a 2 wire connector on the upper right side that go to the back of the throttle body. That one is actually hooked up. I guess that’s the throttle motor. The same side as the 4 wire throttle position sensor. The cut wire connector is on a bracket on the pedal position side

Your car is a very early one made before volume production started. Hard to say what these wires were originally intended for. When the weather improves I’ll go to have another look at mine. There are a pair of orange and black wires. I’ll see if I can trace them.

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Yeah I have orange and black that go to a sensor on the back of the left head, but this is just on a bracket on the tb. Yeah I was told it may have been one of the “fairly early release” xk8s. Seeing as how there would have been several hundred at least that were just for testing or whatever. At least that’s what I was told