Just a follow up on this.Mandrake wrote:Ok ES9J4 owners, I have a little homework assignment for you.
The next few times you drive your car, try the following when starting it:
Turn the key fully on but don't start. Wait a couple of seconds then fully depress the throttle for at least a second then release it. Now start the car.
Take careful note of any change in throttle "responsiveness" during initial driving after the startup, especially light throttle pickup at lower speeds.
I've been trying this on mine and the result is quite surprising, suggesting that the ECU is not correctly self calibrating the TPS operating range without a little "help".
After a morning start, especially if I drive the car gently it often feels almost as if it is sluggish/unresponsive to the throttle or is being "held back" then after a while it will come right.
The TPS on this engine, like many is "self calibrating", where a zero/idle calibration is done every time you turn on the ignition, and a range/full throttle recalibration is done on the fly during driving when full throttle is detected, which means TPS calibration can potentially change in the middle of driving.
Depressing the throttle fully with the key on but engine stopped forces a full range calibration of the throttle for that "key on session" so that the ECU is forced to calibrate idle and full throttle immediately.
Any significant difference in throttle response during driving after doing this pre-start calibration suggests a calibration problem and perhaps a worn TPS. (The TPS has not been changed on this car)
Anyway I'd be interested to see if anyone else notices a difference doing this.
The issue of intermittent sluggish throttle response especially after a cold start has continued for the last 3 months, what I found was that if I very quickly floored the throttle and released it soon after starting the engine or while first driving away that it would usually "rectify" the problem for a while and make the throttle more responsive again. Without doing this it would feel decidedly flat and unresponsive to the throttle and with a significant throttle lag sometimes, so it became a habit to always do this very quick press to the floor of the throttle to "clear it up" after starting the car.
I've been suspicious all along that I was seeing classic symptoms of a "scratchy", worn out carbon track potentiometer, which is all the TPS is. On a scratchy potentiometer twiddling it quickly from end to end sometimes helps it temporarily and this is all that flooring and releasing the throttle quickly would have been doing. Sometimes contact cleaner can help for a while (although i think its a sealed unit that you couldn't get any into anyway) but if the track is physically worn out replacing it is the only option.
So on Sunday I finally fitted a new Intermotor TPS for the princely sum of £11. It turns out to be the best £11 I ever spent on this car.
The intermittent sluggish, laggy throttle response is completely and utterly gone. It has totally transformed the throttle response to how I think it should be. So much so that in these cold mornings with dry salty roads I'm constantly finding myself spinning the inside wheel when I try to accelerate away left or right from a T-junction as the power is instant and strong right from idle. I really have to moderate the throttle carefully on an angled take off so as not to spin the inside wheel. And this is with good almost new Michelins. This is how the V6 should respond.
Pulling below 2500 is now very strong and the throttle response is very sharp almost instantaneous, and best of all it seems to be consistently good all the time now whereas before it was fairly good most of the time (especially if I had done the daily throttle flick) but had spells where it felt a bit sluggish or where there was a large (up to half a second) delay in throttle response. I do about 20 miles a day so I've done 60 miles since Sunday now and it has been flawless the whole time.
When I changed the TPS I made sure not to disconnect the battery, nor did I turn on the key while the TPS and air intake temperature sensors were disconnected to avoid any fault codes being set - basically anything that might cause a false comparison due to an ECU reset or a fault being logged. I didn't want any uncontrolled variables ruining my comparison of old TPS vs new. I've also stopped flicking the throttle after starting the car as it shouldn't need that anymore and I wanted to confirm that the throttle was still responsive without having to do that.
The improvement after replacing the TPS was immediate and overall performance seems to have further improved over the following couple of days as well. So I'm very happy indeed.
It makes sense when you think about it - the TPS and the MAP sensor work together. The MAP sensor controls the overall fuelling based on the air pressure (and engine RPM and MAP tables) however the MAP sensor by its nature is slow to respond - the ECU has to filter out the pressure fluctuations caused by individual cylinders opening and closing their intake valves so there is a certain degree of low pass filtering/smoothing applied to the MAP reading before it is processed by the ECU.
So if the MAP sensor was the only input the ECU would be slow to react to the throttle being opened quickly which would cause a delay in power response and also could cause a lean hesitation due to the mixture not being enriched quickly enough. The lean hesitation/misfire can be detected as pinging by the knock sensor which may pull the timing back causing further loss of power. So the MAP sensor is "reactive" and responds to changes after they have occurred.
The TPS on the other hand is "predictive" in the sense that if you snap the throttle open quickly the TPS will register that change in throttle plate position instantly with only a small sampling delay in the ECU, and before the airflow has actually had a chance to increase since air being sucked into the engine has inertia. So the TPS movement gives the ECU early warning that it needs to enrich the mixture RIGHT NOW to avoid a lean hesitation, which the ECU does by giving the injectors an additional "out of cycle" injection pulse. This happens before the airflow gets a chance to build up thus the lean hesitation is avoided.
One other improvement I notice is that the gearbox kickdown seemed a bit intermittent sometimes - it would sometimes be very stubborn about kicking down, I might be doing 35mph in top gear at about 1500rpm, come across a hill, push the throttle down over half way and it would still not kick down.... Now the kickdown seems a lot more sensitive and responsive than before. So I can only assume a poor TPS reading was causing issues with gearbox kickdown as well, as the gearbox ECU does take the throttle position information from the engine ECU to use to work out when to kickdown and when to change up.
Anyway I'm very happy with the performance now - one by one I've fixed a few niggles here and there including coil pack etc and performance has got better but it is really top notch now. A carbon potentiometer has a limited lifetime and should really be considered worn out after 20 years in a hostile environment like an engine bay and for the sake of £11 to replace it it might well be a worthwhile thing to do to make sure your V6 is running in tip top shape.
The TPS didn't fail outright nor did it ever set any fault codes, however the difference in behaviour and performance before and after is undeniable.
The only thing I would warn about in doing this job is that it is a bit of a pig to get out unless you have the correct Allen key shaped Torx driver due to the close proximity of the LHM tank. I managed to struggle by without one using an Allen bit from my socket set turned with a spanner but it was very awkward, and I found that both bolts were tight nearly all the way out and back in again despite adding grease. So the correct Allen torx key is definitely recommended! Then it would be an easy 10 minute job.