'06 XK8: have a slight engine surging happening when at cruise around 45mph; can see tach needle jumping and feel it. Takes only a slight change in pressure of right foot, either more or less and engine surging stops.

At first I thought transmission is slipping, but after a few more miles I think the problem is the throttle position sensor(s) (TPS).

Did a quick checksearch and could not find any threads on this and also could not find any throttle body parts other than the gasket.

I cleaned the throttle body when I replaced the octopus heater hose a few months ago so I doubt the TB needs cleaning.

Any other thoughts?

Thanks

 

The throttle position sensor TPS may need replacing. But first try cleaning all the connectors to the body with electronic cleaner.

Disconnect the negative battery cable before proceeding. This will also require the ECU to relearn the settings of the various modules, so the car will run/shift a little different initially.

If that doesn't resolve the problem it will probably be necessary to send the TB to a rebuild service, such as ASI.

 

I wll clean the TPS connectors today as I will be doing an oil and filter change anyways.

Looked-up ASI and according to the web page, only up to the 2003 throttle bodies.

So I am at a loss as to where to go now with my 2006 XK8 throttle body for parts or rebuild.

Thanks

 

You're jumping the gun, and imagining the worst case scenario.
Have you checked for codes?
Do the basic stuff first, clean the throttle body, eliminate poor connections, harness problems etc, before considering the most expensive, most difficult, worst case.
Most of the time, it's not...
Regards,

 

Yes, my fault for not noticing the year.

 

White Bear: I have not checked for any pending codes and I will do that. TB is not dirty as like I said I cleaned it a few months back and it is still looking pretty darn good.

As the surging only occurs at a certain cruise speed and just a slight change in right foot position stops the surging....I really doubt that there is any type of harness problems as I would think the surging would occur at other times.

I did clean the TPS contacts today while changing oil/filter...have not driven it yet.

It seems like the problem is caused by a "flat spot" in the TPS. Guess I could be an ohm meter on the TPS terminals and check to see how the resistance changes during travel. Sure wish I had kept that old analog multi meter.....it would have shown a change much better than the DMM I now have.

Thanks for the responses.

 

TPI output is voltage, and can be up 3 different outputs. Two will go from 0-5 volts, one will go from 5-0 volts. If the ECM sees any variation, then the engine will go to idle.

 

Did you have this problem before you replaced hoses ? Agree with above getting code but especially getting fuel trim readings.

 

If it does turn out to be the TPS then still don't despair as (despite what Jag dealers tell you) you can buy them separately without having to buy a complete TB. They come up on eBay quite often both as used original (I wouldn't as no telling if it will fail also) and new aftermarket or occasionally OEM. I bought 2, kept one as a spare and sold one on.

 

White Bear: True the TPS output is voltage when connected, but I ws going to remove the connector so I could access the TPS terminals and that is why I said resistance instead of voltage.

jamdyers: no did not have this problem before replacing the coolant hose...but there were 2 months inbetween them. My scanner will pull codes, but will not give me fuel trim readings.

worrasf: Good to hear as it appears that the TPS easily unbolts from the TB on the version used on my '06 XK8; unlike earlier versions. I will have to voltage readings at idle so I can set the replacement TPS when I find one. If it is indeed the TPS that is causing the surging.

 

Finally hooked-up my code reader: pending codes were P1111 and P1797.

P1111: no problems
P1797: had a problem one day with the neutral safety switch many months ago and only happened once, so likely left over from that.

Wife says surging is getting worse. Looks like time to take to dealer and have then connect their scanner.

 

I'd next watch fuel trims.

 

I vaguely remember reading a thread about a year ago where someone pointed out that NAPA carried a Toyota TPS that was the exact same part. If you need one see if you can find that thread.

 

Going to the dealership on 12/14....will see what they have to say. Thanks for the info on the Toyota TPS....will look that up... just in case. Will update.

 

Lets take a step back on this problem and refocus. If you had a problem with the TPS or the PPS you would have a code for it. To date I have yet to see a throttle body problem that has not thrown a code. They have a redundant tracking and sensitive to fluctuation problems.

Use your codes to guide you!! A P1797 code is a transmission issue and can be related to the Transmission Control Module or with the Valve body in your transmission. It could be an ECM problem but from my recent experience and my gut tells me your problem is in the TCM and/or your Trans Valve body.

Link http://jagrepair.com/DTCforms/X103_P_DTC_OBDII_R1.pdf

As a note ASI can test and repair your TCM and the valve body can be replaced.

 

Thank you Gus!! Valuable information; I will be researching the TCM and valve body to learn more about these.


Thank you once again.

 

I recently experienced near the same issue and will be writing a procedure on it soon.

Remember that this ZF trans is electronically shift it gets its commands from the TCM that gets information from the ECM on what to do and when. In my situation I had a problem with the TCM and one of the solenoids in the valve body in the trans. It was doing the same thing yours was doing a surging at 60mph.

Keep in mind that it may not be your problem but your symptoms sound the same.

 

Xk8 is at dealership now; in talking with service advisor I told him that I had cleaned the throttle body a few months back and he then told me that I should NEVER clean this TB! He did not give me any other details as to why just that I should never clean this TB.


Anyone know anything about this?

 

The coating on the TP. Cleaning with a soft rag is not a problem.

Gus
www.jagrepair.com

 

Well news from the dealership...needs TCM replaced...estimate is $4200 or so....wow!....was not expecting that price tag!

So going to just live with the surging for now....until it gets worse or something breaks or I find a more reasonable option.

AAARRRGGGHHHH!!!!!