How does Pscan compare to T4

pscan.uk wrote: Air leak or warped throttle body?

Checked. It has the proper pre-tensioned clip that came originally with the car, not like a jubilee clip. No air leaks detected and checked routing of all air hoses. Stumped as to what the cause of the periodic high idling after 15 minutes of driving. All pscan readout (incl water temp) all within spec except when this issue hits and no. of steps rise to 60-70 steps (RPM ca. 1500) from the 21 steps (875 RPM).

Throttle position switch worn?

I think if you have an air leak the stepper position will drop to zero.
It might be useful (if it's not difficult) to deliberately create an air leak to validate this.
My understanding is that the ECU sees that the revs are too high and tries to close the throttle but can't close it below zero steps.

pscan.uk wrote: I think if you have an air leak the stepper position will drop to zero.
It might be useful (if it's not difficult) to deliberately create an air leak to validate this.
My understanding is that the ECU sees that the revs are too high and tries to close the throttle but can't close it below zero steps.

Could a leaky valve stem cause this anomaly? Would it be worth it running a live check the fuel Balancing across the four cylinders?


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I did find that the hose to the throttle from the IACV was back to front¦ it was rubbing up against the throttle position sensor until I turned the hose around but I doubt this will be the fix.

The TPS is new.

I have gone back to basics - I have adjusted the throttle idle valve to ensure that the physical throttle degree is ca. 4 degrees off the vertical. I have reset the TPS so it knows that the throttle is at 4 degrees at idle - at cold it is idling steadily at 1200rpm. Next week I will then test to see what happens on the idle RPM and stepper before, during and after a decent run, with PScan live data.

One thing that I have noticed from the PScan live data is that when the idle rpm rises to 1500 after a decent run, the stepper has risen to circa 60 steps. My logic would say that the car thinks that the throttle is closed (0 degrees or closed), so to get extra air it is opening up the bypass....resulting in too much air and therefore higher idle revs??????. Would this, therefore, indicate that the problem is the TPS, although the TPS is new?

Thanks for the other suggestions which I will follow up.

Did you do a TPS reset?
I expect you did but one still needs to ask as part of the process of elimination.

Yep - TPS reset.

Went for a run today. All perfect after several years of frustration including replacing many sensors and stopping me from using and enjoying the car. Idle steady at circa 875 rpm during and at the end of the run instead of finishing up at ca. 1500 rpm.

I think that the problem was caused by one of the following:

1. The throttle was not at 4 degrees off the vertical so the TPS was being reset at 4 degrees when the throttle was not physically at 4 degrees. Solution: Went back to basics and checked that physically the throttle was as close to 4 degrees at idle as possible using a piece of marked-up piece of paper. When the engine was hot, the stepper was showing 0 steps so I adjusted the idle stop screw so that the stepper was at 25 steps - this was 1/2 turn of the idle screw from where I had set it after the checking the throttle opening physically. I then reset the TPS on the basis the throttle was still close to 4 degrees off the vertical at idle.

2.The hose going from the throttle body to the IACV. It was the wrong way around and was perhaps putting 'pressure' as the car become hot, perhaps not by much but enough on the TPS (which I thought was poor design) to create my problem. Solution: I turned the hose around so no fouling of the TPS. I suspect the hose had been turned around by me during one experimentation using a silicon hose a couple of years ago and this was the start of my problems. Hint: On the hose, one end is a marked line in white on the hose - this attaches to the IACV.

Thanks for all the suggestions. Always appreciated. My take away is that the combination of Pscan and getting back to basics is a must to solve some problems on this car.