TPS advice - engine will not rev over 1500rpm

[ITVRI]

Away on holiday in Cornwall my Chimaera developed a problem in that it would not rev past 1500 rpm, the rpm returns to idle while keeping my foot on the accelerator revs again to 1500rpm and drop to idle.
If I dip the clutch and hold the accelerator it quickly rises and falls continuously.
If I change gears before 1500rpm it appears to be ok.
I connected my fault reader and it showed 18 indicating the throttle position sensor.

To get myself home I found if I started the car and then disconnected the TPS it ran ok and it got me back to London with a record MPG ( 300miles to the tank)

I ordered a replacement part ERR2263 and replaced the old TPS but the symptoms are still the same. There is no fault coming up on the code reader now and I understand that the TPS on the serpentine motors are self calibrating.

A similar thread describes the exact same symptoms and the fix was to change the TPS
http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Has anyone had any similar experiences like this and any ideas of how to fix this issue?

My next step is to buy a cable for rovergauge and see what it may reveal.

Cheers Warrick.

[Julesprivate]

IIRC correctly 1500RPM is the safety threshold for the ECU "high idle", in the absence of a TPS voltage showing the throttle is open the ECU limits the revs to 1500, I believe this is in case of an air leak that might otherwise allow the car to overrev and cause damage.

It still sounds like an issue in the TPS circuitry. It may be worth doing a quick ECU reset (battery off, wait, battery back on) but you probably already did that.

Did you test the TPS voltages before replacing the unit? Or do a resistance check when you had the TPS off the car?

For Serps the connections are:

Brown = 5V Rail from ECU
Green = Signal Wire
Blue = Ground

Leave the TPS connected. Start the engine and check that the voltage reading is 0.32 – 0.34 Volts.

If the reading is incorrect then slacken the mounting screws and rotate the TPS to achieve the correct reading - if you don't have slottes screw holes you may need to elongate them..

Then I'd stop the engine but leave the ignition on and test the full voltage range to see if it rises smoothly) - with a new TPS you shouldn't have any issues!

Just out of interest did you set the base idle whilst you were there? It shouldn't make a jot of difference to the symptoms you have but it's the ideal opportunity to do that too..

It may also be worth checking the MAF (i.e. run with it disconnected for a short while) this will put the car in to limp home mode but quickly iliminates this as a potential problem.

[ITVRI]

Thanks for your tips Jules.
I did not check the old TPS before replacing.
I purchased the Rover Gauge lead from Blitzracing and uploaded the program to a spare laptop which showed me that the new TPS was not giving a signal. I removed the new TPS and manually turned the pot "screw" while viewing the readout on the laptop. The TPS decided to work sometimes but most of the time not.
I then swapped the new TPS for my old TPS which again was not perfect but not as bad as my new one.
I checked the new TPS with a multi meter which showed no change in the resistance
I assume that the the new Britpart no name TPS is not worth the £90 I paid for it.

I really recommend the Rover gauge to anyone wanting to do their own diagnosis of symptoms.