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        General >> Problems >> Throttle Position Sensor. (TPS)
        
(Message started by: Spannerdemon on Jan 26^th, 2007, 10:23pm)

Title: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 26^th, 2007, 10:23pm

As some of you will know, I've been having nightmare problems with the idle on my 12v 2.9. for quite a while now.

Nothing seems to be curing it, but today I had what I hope is a breakthrough. :o :o :o

An American website specialising in the manufacture of TPS units, (and believe me I've dug really deep for answers here), recommends simply disconnecting the wiring plug from the TPS. According to the experts on there, if the idle then returns to close to what it should be, and the car runs OK, then it shows the TPS to be faulty.

I was a bit sceptical, and thought, well it can't be that easy, but then I thought, well why not?

So, this afternoon, I did just that..............., took the plug off, and guess what? Much to my total amazement, the car is now idling steadily dead on 850rpm, without any ill effects whatsoever. It runs fine, and I have since done about 40 absolutely trouble free miles. At every set of lights, or pedestrian crossings the idle is constant at 850 rpm. Basically the problem has gone.

It hasn't run like this for weeks.

So the question is this. Do I need the hassle of this TPS? IS it faulty, and I buy a new one, or should I just leave it disconnected? One thing is for sure, when the plug IS connected, I get all sorts of problems. When it's off, the car runs fine.

Any advice welcome, but I can tell you that after many weeks of having the revs jump to 2000rpm at every set of lights, driving it now is absolute bliss!

Really interested to have this explained. :D

I will buy a new TPS if need be, but I don't want to fork out the best part of £60 just to go back to square one.

Thanks for any ideas/advice. :D

Title: Re: Throttle Position Sensor. (TPS)
Post by cossieguy on Jan 27^th, 2007, 8:36am

My surging idle problem was cured by removing the TPS plug and reseatting it. Does your bad idle return when TPS is reconnected if so I think you've got your answer. Thanks to my dying engine(I've got a replacement off a car with 42,000 on clock for £400 coming next week) i've learnt a valuable lesson about these cars, if you think it's dodgy change it, these engines are at least 9 years old and most are older they're not going to run forever in their original form things are going to break. So best change them at the earliest oppurtunity before they cause anything terminal.
Guy.
PS My engine is coming from a company called RPS limited(Rare Panel Specialists) who sell engines on ebay. Anyone heard or had any dealings with them?

Title: Re: Throttle Position Sensor. (TPS)
Post by Simmo on Jan 27^th, 2007, 8:41am

S/D, Just a thought but could it be that by disconnecting the TPS the system has reverted to a form of 'limp home' mode?. I'm sure one of our experts will have a view soon. :)

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 27^th, 2007, 8:42am

Thanks Guy.

Yes. It returns. So I suspect that this 'wonderful' USA site that I found, has provided me with the answer, which has been eluding me for weeks.

Good advice from you here, which I entirely agree with. I think sometimes that we all tend to forget that our Super-Scorps, do get old!!

I've just got off the phone to our nearest Ford Dealers.

I'm getting a new TPS sent for early next week, along with the gasket, and hopefully, that will be the end of it. Time my baby had a new part. ;)

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 27^th, 2007, 8:46am

Quote:

Just a thought but could it be that by disconnecting the TPS the system has reverted to a form of 'limp home' mode?

Don't know Mike. :-/

All I DO know, is that it's now running 100%, and has now covered over 50 miles since I removed the plug.

New part ordered anyway. Although I'm going to cancel the TPS gasket and cut my own. £9.00 with the VAT for a gasket that's 2" long.........I think not!!

Title: Re: Throttle Position Sensor. (TPS)
Post by scorpio_man on Jan 27^th, 2007, 10:26am

hi sd

before the new one arrives, give the wiring a look over for any cracking.

years ago, we had a 2.0 (eddie) that wouldn't start because of dodgy wiring to the tps, so it does play quite a big part in the good running of the engine.

hth

Title: Re: Throttle Position Sensor. (TPS)
Post by TiberiuS on Jan 27^th, 2007, 1:58pm

SD, not sure how it's running ok as the TPS is the thing which controls the fuel/air mixture going into the cylinders, also controls the autobox (not sure if the 12v is this electronic?) and has an effect on ignition timing I believe.

You may be very lucky on the 12v as it's like a hybrid between the new and old engine management, not hopeful that it'd work on the 16v or 24v though :(

If I disconnect it on the XJ, it goes into limp home mode and the amber 'check engine' light comes on, I don't even think it'd restart without it. Kickdown, sport mode, gear shifts, fuel mix, timing are all controlled by it, if it dies then the entire engine management goes belly up along with fuel economy...

I got myself a second hand one and soaked it in meths and switch cleaner, just be careful where you drill the 1.5mm hole for the cleaner ;). It's not perfect but the car does idle ok now and do kickdown (any car which can pin you against the seat in full flight is worth a new TPS ::))

Main dealer wants to rush me £140 for a new one...

Regards, Bruce.

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 27^th, 2007, 3:15pm

Still running beautifully. I've just got in from work (another 25 miles) so that's close on 80 miles now without any problems.

Wiring is OK, and was one of the first things I checked.

I'll fit the new TPS when the dealer gets it, and go from there, but driving at the moment is bliss, compared to what it's been recently.

There are absolutely NO bad side effects. Fuel consumption remains good, idle is 100% and everything seems to be fine. Starts first time every time (which again it wasn't doing), and runs from hot or cold without any problem. Baffled as to what this sensor actually does, because without it, the car is fine. :)

Title: Re: Throttle Position Sensor. (TPS)
Post by scorpio_man on Jan 27^th, 2007, 4:50pm

hi sd

did you check the voltage output of the tps as per that site you posted?

might be interesting to see what it is compered to the new one.

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 28^th, 2007, 8:06am

Yes. Did this. I was getting 0.6 volts. That's low, so may be the problem.

I understand that the new one should be within 0.8 to 1.0 volts (so 0.9v for optimum performance) but will check it on fitting.
I'm using a voltmeter between the battery earth and the greyish wire on the sensor plug.

Still baffled though as to why it's running perfectly well without it!!

It's as though it never needed it in the first place but it's getting replaced anyway, as I'm sure it may have an effect on emissions, and my MOT is looming!

I have to be honest though, and say that if the MOT was not due, then I'd be leaving it exactly as it is!! :D

Title: Re: Throttle Position Sensor. (TPS)
Post by mr._floppy on Jan 28^th, 2007, 10:26am

It must be that the TPS is less crucial for the 12v that the 24v.

Still , one would think it would make some difference to ignition timing and auto gear changing .

Does your trip computer still show an accurate MPG figure ?

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Jan 28^th, 2007, 4:56pm

Yes, everything is running 100%. I really can't fault it in any way at all. If anything Fuel Consumption is exactly as before, and I know how much I use going to work and back. Hasn't changed.

Gear changes have never been a problem, and I have a really smooth box. Certainly no worries there.

Weird it is!! But I'm happy. No more THUMP when it goes into Drive at 2000 revs, and no more sitting at the lights at 2000rpm watching my expensive fuel burn away.

Really can't explain it, but it's here, and running beautifully again if you want a test drive!! ;D

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Feb 1^st, 2007, 5:24pm

OK. Here's the outcome on this business.

Today I removed the complete throttle housing. No wonder things haven't been running properly. The previous owner has been taking short cuts!!

Why DO people botch things when it's easier to repair them properly?

No gasket on the TPS. No gasket between the Throttle Housing and the EFI Plenum Chamber. The TPS IS broken. The muck inside the Throttle Housing was mind blowing. Really filthy on the engine side.

So, a full clean and rebuild with nice new gaskets, and a brand new TPS, and a new air-filter and all is well again. There must have been so much air getting into the system generally, that trying to set an idle was just not possible.

Bit of a nightmare getting there, but all OK now.

Many thanks to all of you who have tried to help me here. it's been much appreciated. :D :D

Title: Re: Throttle Position Sensor. (TPS)
Post by Simmo on Feb 1^st, 2007, 9:09pm

Well done S/D. Glad you've fixed it. ;)

Title: Re: Throttle Position Sensor. (TPS)
Post by Spannerdemon on Feb 1^st, 2007, 9:22pm

Thanks Mike.

Lovely to drive again, but still baffled as to why it will run without a TPS at all. I think that's going to be a mystery for a while.

Anyway. All's well that ends well. :)