1988 Sapphire with 330 bhp kit.
Runs fine when accelerating, or when I lift my foot from the gas pedal.
If I dare try to maintain a constant speed, the car has the hiccup: like the engine is suddenly stalling then starting again... and again, and again!
Not comfortable and worrying for the transmission.
Help appreciated!

 

I'd buy a sensor kit and change all sensors.

 

Only a guess but could have an air leak after the throttle body creating lean mixture which is not noticed when giving it some right foot, only when cruising at constant speed?
Might be worth checking out - could become expensive if left.

 

Throttle position sensor...if you had it hooked up to a monitor I'd guarantee that it's intermittently breaking contact between 17% and 21%, which is the general "cruising" throttle position.

 

TPS if u drive the car all fine until u let the acceleration pedal of FULLY !
then starts to play up means not set correctly !best checked with a Pectal or Collins monitor

 

Does it drive PERFECT unless you do that, or just better ?, just loosen the tps and move it to see if the point of trouble moves, it could be other things as well.
tabetha

 

OK, thank you all...
Stevo, I had already checked for some airleak.
The car drives perfect on all other ocasions: idle at cold is just over the lower dot, and just below the upper dot when warm. When I hit 3500 RPM, it looks like some jumbo jet just hit my rear bumper!
I have a free day tomorrow, so I'll have time to check the TPS problem. What value should we read on the computer?
Other question: is an RS500 TPS the same as my RWD Sapphire's?
Thanks again!
PS Tabetha, what other things are you thinking of? I could test them tomorrow as well at the tuning garage... though last time I went there, the man told all sensors were giving correct values???

 

Yes, they're the same - they are marked PF01.

Output voltage from the TPS should start at 5 volts with zero throttle, then step to 4.5 volts before falling down linearly to 0.5 volts at wide open throttle. The diagnostic function of the ECU will only log a fault if the sensor's disconnected, or shorted, so you do need some kind of constant monitor so you can spot the fault when it happens. A passenger with an analog volt meter would be better than a digital meter for this purpose, and a proper engine monitor would be infinitely better than that.

Ideally you need to constantly monitor the output of the sensor while you're driving it - it will be difficult to reliably test it while the car's stationary as chances are there'll be no fault unless the vehicle's actually moving.

 

Right: it only happens when moving.
Thank you.

 

Don't worry if the value isn't exactly as it should be, they rarely are with old wiring.
Any missing spot on the tps can be impossible to trace, even when there with a multi metre, as there is so many points of output on a tps.
How old is the fuel filter ?, if it has a old filter that is partially blocked this can cause it, due to it running lean, under acceleration it has the extra fuel so it isn't a issue.
tabetha

 

Filter and pump are nearly new (about 2500 miles).
I'll check it anyway...
Thank you.

 

Further to my previous post, after having a long hard think, I seem to remember that the ECU won't actually report a fault with the TPS at all - it will reports faults for every other sensor though. A bit annoying that, really.

If you replace the TPS, it'll need setting up too, ie, securing in exactly the right position.

 

Well, today the damned car ran perfectly all day long, many miles done, and the hiccup started again 100 yards before reaching my home...
I am getting crazy.

 

Mine was exactly the same, the fault only got spotted because a monitor was attached to the ECU.

 

TPS buying time, then, probably...
I'll check on the net.
Those things are expensive (in relation to Portuguese buying power, anyway!)
Do you know about other cars (maybe Italian)using the same part, by the way?
Thanks.

 

Funny you should ask that...Ducati bikes, Lancias and Ferraris used them. The PF01 you need may be difficult to get hold of - your best bet for those is to find a Cosworth being broken for spares.

The PF09 which replaced it on the 4x4s is slightly easier to get hold of, but they're expensive new.

 

I think the pf09 is becoming difficult and expensive to get also it wont be correct if your on a L6 , a recent thread in rs500/saph/3 door room that stu at MSD answered has all the info you,ll need

 

Couldn't find the thread...

 

20 mins of searching i found it , for some reason i,m unable to copy the link . Type 'Throttle position sensor ' in your search bar, you,ll need to scroll down until you see a thread called this^^ .

 

Thank you opposite lock, I'll check as soon as I have some free time.