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Saxo Engine/Performance If you're interested in tuning Saxo engines, or if you need to know something which is engine related... this is the place for you.

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Old 5th April 2020, 19:56   #1
sri_130
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Default TPS knackered - or something else

Has anyone actually had a TPS fail/go faulty etc etc?

I think I've got the symptoms, but never had one pack up on me before.

Car starts first time, idles nice for the first 5 mins. It then hunts a little.
When applying the throttle, the initial application is like it bogs, ever so slightly.
When it's warm enough to open the thermostat fully, it's still hunting but doing it that quick, it turns into a hum! a few minutes after that, it actually struggles to idel and dies.

I disconnected the MAP sensor (when engine was warm) and it ran like sh1t. Wouldn't idle and backfiring on applying some throttle. To me, that must mean the TPS is screwed?

I have found a brand new Magnetti Marelli TPS, that must have come with the car.. so I think I have the probable cause, but I've never had one go before.

Coil pack has been replaced, MAP is new, new lambda, no codes btw.
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Old 6th April 2020, 14:21   #2
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Mine misfired like a bitch on anything above very light throttle once, had me scratching my head as Id changed loads of stuff for known goods. Turned out to be moisture in the tps connector, so possibly!
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Old 11th April 2020, 23:14   #3
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If you are checking codes, does this mean you have lexia? If so, then check throttle position. On later cars, it will show percentage or degrees of open, on early ones you just get idle, mid and full.

One thing you could try, is just to rule out the Idle control valve. Start the car, wait a minute or two then disconnect it. Car will run fine with the Idle valve disconnected. ActuallyI often disconnect mine if using on the track as it allows the revs to drop quicker which is better for quick gearchanges. If that makes no difference you are likely looking at TPS as the only other thing to try.

Cutting out after rough running, however can be the lambda (though you say have changed that) . On my car with a broken wire in the cable to the lambda sensor, the car was fine until warm (lambda is ignored until past the temperature considered to be warmed up by the ECU). Then it would start to run rough, get worse over the course of a minute say, then die. Start up straight away again fine and repeat the cycle. Basically the ECU was wrongly adapting the fuelling based on the lambda signal (which was wrong due to the broken wire). Once the car was restarted, those adaptations were cleared hence it could run again and repeat the process.

Again, if you have diagnostics you should be able to look at the lambda reading, it should fluctuate between around 0.1V and 0.7V (roughly, main thing is that it should swing around within roughly a 1V range) - when warmed up. If it is stuck at a set value then there is still an issue with the lambda, e.g. wiring issue since you have changed the sensor.
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Old 28th April 2020, 21:07   #4
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I don't have lexia no - it's a Mk2 2003 Saxo.

So I bought a new TPS. Threw that on.
The hesitation in applying the throttle has gone completely. (RESULT).

However the car still idles somewhat peculiar. Now it seems just a little all over the place. Sometimes up 500 rpm or so for 3 or 4 seconds, sometimes near stalling, sometimes fine.
It does this straight from the off - Stone cold, immediately poo idle. So it can't be the lambda as that is ignored early doors.

I disconnected the MAP sensor whilst it was running - the car idles nice! no hesitation on the throttle as well. F*cking MAP sensor again.
Already swapped it for a second hand one from the breakers (Mini R56) as it was even worse before. Coupled with the knackered TPS, what a wreck this thing is.
Just gonna buy a new MAP.

Last edited by sri_130; 28th April 2020 at 21:09.
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Old 28th April 2020, 21:10   #5
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Quote:
Originally Posted by dturbo View Post
If you are checking codes, does this mean you have lexia? If so, then check throttle position. On later cars, it will show percentage or degrees of open, on early ones you just get idle, mid and full.

One thing you could try, is just to rule out the Idle control valve. Start the car, wait a minute or two then disconnect it. Car will run fine with the Idle valve disconnected. ActuallyI often disconnect mine if using on the track as it allows the revs to drop quicker which is better for quick gearchanges. If that makes no difference you are likely looking at TPS as the only other thing to try.

Cutting out after rough running, however can be the lambda (though you say have changed that) . On my car with a broken wire in the cable to the lambda sensor, the car was fine until warm (lambda is ignored until past the temperature considered to be warmed up by the ECU). Then it would start to run rough, get worse over the course of a minute say, then die. Start up straight away again fine and repeat the cycle. Basically the ECU was wrongly adapting the fuelling based on the lambda signal (which was wrong due to the broken wire). Once the car was restarted, those adaptations were cleared hence it could run again and repeat the process.

Again, if you have diagnostics you should be able to look at the lambda reading, it should fluctuate between around 0.1V and 0.7V (roughly, main thing is that it should swing around within roughly a 1V range) - when warmed up. If it is stuck at a set value then there is still an issue with the lambda, e.g. wiring issue since you have changed the sensor.
Unfortunately my 3 plug ECU has the software version that limits obd output to next to f*ck all. I need to ask Wayne to stick the correct revision on it, when I take it back to get mapped again.
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Old 28th April 2020, 22:44   #6
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Unfortunately my 3 plug ECU has the software version that limits obd output to next to f*ck all. I need to ask Wayne to stick the correct revision on it, when I take it back to get mapped again.
That's a bastard, my 3 plug ECU in my GTi is like that.

Can see engine rpm, battery voltage and that's about it
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Old 29th April 2020, 12:02   #7
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That's a bastard, my 3 plug ECU in my GTi is like that.

Can see engine rpm, battery voltage and that's about it
Yeah likewise.
Before, I did get a few other interesting bits. MAP info for example, Lambda I think - decent stuff.

I blame Wayne. Maybe he should setup a postage return system to get a decent software revision on it... now there's a lockdown business idea....
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Old 29th April 2020, 19:18   #8
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Previous owner left a MAP sensor in the glovebox!
It was sealed but not new, genuine Bosch thing he bought.
Stuck that on, runs like sh_t. Unplugged it, runs fine again. 3 map sensors faulty? Or do codes or some reset thing need to happen before trying another one?

Order a new one though, but got a feeling it'll be the same again.
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Old 29th April 2020, 20:51   #9
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Originally Posted by sri_130 View Post
Previous owner left a MAP sensor in the glovebox!
It was sealed but not new, genuine Bosch thing he bought.
Stuck that on, runs like sh_t. Unplugged it, runs fine again. 3 map sensors faulty? Or do codes or some reset thing need to happen before trying another one?

Order a new one though, but got a feeling it'll be the same again.
I went through a similar rigmarole, my ecu was fucked

Send it to wayne and ask for TPS only base map, then go for a dyno sesh.
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Old 29th April 2020, 21:23   #10
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I went through a similar rigmarole, my ecu was fucked

Send it to wayne and ask for TPS only base map, then go for a dyno sesh.
LOL. Balls, I hope not!

It's already been to Wayne, it was mapped a year or so ago - I bought it after it had been sat outside fucked. I think I'm getting somewhere though, I shall persevere! Make do and mend.

Just landed on a snap-on MT2500, see if I can read some data of the old gal. if not, I saw Wayne using one on mine, so it'll be useful for that (if I ever get it going again).
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