Hello every one,

Car decided to throw a fit today, i was playing a little with the accelerator, going slow over speedbumps, not pushing the brake pedal to try to figure out where a suspension noise was coming from, and suddenly the trans red light came on and the car started idling really high. Shut the car down and restarted it and still did it. Shut it down again and went to check on the TB connectors to see if something was unplugged and restarted fine with the transmission light gone.

What could have caused this?

-going over speed bumps slowly not pressing the brake (confused the TPS?)
-going over speed bump made something in the TB come undone?
-need new TB?

Any one with any experience on typical p0121 please reply.

Thanks !

 

Well you could start with a tune up and make sure everything is in order. Here is a check list:

jaghelp.com: That pesky rough idle

P0121 is caused by a problem in the throttle position sensor circuit. I hate to say it but they do go out. Check everything in the list above and hope, otherwise you probably need a throttle body

 

Thanks for your response!

I forgot to add that the code reader said p0121 "a" pedal sensor, so I am wishfully thinking that because I was letting the car roll with no acceleratir pedal input it just got confused. But if that s not a possibility I better start looking into new throttle bodies. No sense in delaying the inevitable

 

Anyone else has any ideas? Just buy the new throttle body?

 

Looks like your car behaved exactly as forecast in the Jaguar list of default actions for P0121. They are:
– Throttle motor and throttle motor relay disabled
– Throttle valve opening set to default value
– Idle speed controlled by fuel injection intervention
– Idle speed adaption inhibited

The listed possible causes are:
TP Sensor to ECM wiring: open circuit, high resistance
TP Sensor to ECM sensing circuits (TP1 or TP2): short circuit to B+ voltage
TP Sensor failure

Hopefully, as the situation resolved when you checked out the TB connectors, the problem is there! Take the connectors to the TB and the TP off and give them a good clean with electrical contact cleaner. Ensure all pins are corrosion free and see what happens!

 

My 04 X-Type did this to me when we went for our Christmas vacation (300 miles away from my house). I didn't do anything to the car to cause it to give this error but the idle was raise, transmission light was on, CEL on, and the same error code you gave. Luckily i've had success with solving this problem before on my 02 X type.

The next day I went to find an autoparts store and had to buy a set of tools/sockets, pliers, electrical cleaner, throttle body cleaner, black silicone gasket maker, and some dielectric grease. I bought the cheapest stuff I could find and spent around $40 for everything.

At my hotels' parking garage I began disconnecting the TPS sensor, the Throttle Body connector and all the stuff in the way. First, make sure nothing is physically stuck between the throttle body plate and the rest of it. Then, proceed to clean out the TB with the dedicated cleaner. Remove the TB and use your pliers to undo the weird 5 star bolt that jaguar uses on the TPS (take a picture before removing it to see how to exactly put it back because the TPS is the adjustable kind).

Open the TPS and spray electrical cleaner all over it and onto the base on the TB. Let it dry and put some dielectric grease in the center and on the metal that makes contact with the base. Use the gasket maker to make sure no dirt or water manages to creep inside again and put it back. Clear the codes and start it up. This worked for me and I was able to drive all the way back home and after 300 miles it gave 0 problems or hiccups.

Hope this helps. The TPS is a really primitive piece of engineering both mechanically and electrically; not much to it other than some spindle and a potentiometer that is physically moved when you open and close the TB.