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  OBD2 - Poor Running TPS

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OBD2 - Poor Running TPS
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OBD - Throttle Position Sensor

TPS out of Synch


Recently, despite having a very expensively reconditioned autobox, my Cosworth started to thump slightly into gear. The engine, normally sweet as silk at idle, also started to sulk, idling strongly and causing a lurch when selecting D from rest.  This was not good; I had a buyer for it and I had boasted about how well the car ran.

I ran a diagnostic using the OBD lead, and sure enough, I found a DTC on the CODES page;


P0122: TPS circuit low input

Wow, bummer. I looked at the DATA page and selected the TPS sensor. I know from experience that it will show 16.1% when not depressed; other vehicles, BMWs for example, show 0%, but all our Scorpios have a resting rate of about 16%. The DATA page showed me the answer;

Ooops; only 4.7%. For the Scorpio, this is far too low for the rest position.

There was the answer; 4.7% is simply wrong for the Scorpio - the EECV expects a value of about 16%. What had happened? The EECV had gone out of 'synch' with the TPS. This happens from time to time; perhaps the throttle had inadvertently been pressed when turning on the ignition, or perhaps there was radio interference. Whatever the reason, this was the cause of both the poor idle and the thumping gears. The TPS is an input for gear changes and fuelling, so both functions would have been effected by the faulty initial position recorded by the EECV. Somehow, both had to be re-synchronised to the correct figure.

Luckily, I knew how. The TPS - and all the other sensors of variable output - can be reset to base by the simple method of disconnecting the battery for half-a-minute. Be prepared for awful running, perhaps stalling for a few moments afterward because all of the fuelling parameters have to be relearned - but once that has happened within a few minutes the idle will smooth out and the auto gearchanges would be like silk once more. Make sure you have your radio codes, though. If you haven't, someone on the Forum or the List will be able to get them for you.

I disconnected the battery, checked the TPS connector for both bright connections and the presence of the special grease - both okay, then I reconnected the battery. Then I popped the OBD lead back into the plug and checked the TPS - yes; 16.1%, the normal for my Scorpio.

A quick test drive confirmed that normal idle and perfect gear changes were restored. This is a very worthwhile check to carry out if you experience a poor idle and bad gearchanges.




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