Hi folks. Haven't been around here for a while but thought I'd post this one up.

I've just unplugged my tps and gone for a drive. The car drives so much nicer, in exactly the way I wanted... I'm quite pleased Smile Gone is the stupidly annoying 'on / off throttle' jerking back and forth, that made smooth gearchanges and heavy traffic such an exercise in throttle control and timing. With the TPS operational, every time it sees 'no throttle' the ecu shuts off the injectors. I'm quite sure many cars do similar, but they all seem to manage it much more smoothly than the fc. Previously, if I'd quickly tapped the throttle on off on off on off, the car would shudder massively and make all sorts of clanging noises... now it's pretty comparable to other cars on the road. My TPS has always been set correctly and this little glitch has bugged me since I've owned the car.

The idle is slightly lower, I assume because there is no longer a 'this bloke has his foot off the throttle, supply idle control air' message to the BAC valve. I'll fix this at the throttle butterfly.

I'm posting this up for other peoples info, and to ask if anyone is aware of any problems with this? My understanding is the tps is only used for idle control on s4's? There was a wide range tps added on the s5 to control the OMP, but the s4 just uses a mechanical linkage?
I expect fuel economy might be very marginally worse, but it may also be unnoticeable, I'm not sure. I'll post up when I know.

 

When the ECU doesn't see a TPS electrical input, it uses a stored throtle position setting to keep the car running. I believe it's 18* throttle angle (don't ask me where they set the protractor for that one, lol), or what Mazda calls 100% throttle. Yes, gas mileage will most likely suffer, because the ECU won't be able to sense decel (throttle lift) anymore, so the injectors will keep firing when they otherwise wouldn't...

Fix it?

 

well, the ecu will provide enough fuel for the air being drawn in. So it'll be like idleing instead of nothing. Maybe fuel economy will be substantially affected, we'll see. As for 'fix it', the point of my post was to explain that I felt I *had* fixed it Just wondering if anyone knows of anything the tps controls other than idle.

 

It's input is used along with several other sensors to schedule fuel up to approx. WOT conditions. It's not just an "on-off" switch for the idle...

 

air fuel ratios are exactly the same as before, (aside from some occasional rich measurements with a closed throttle) according to my narrowband anyway. Which was expected, because the tps is at full output by the time the throttle is a third open...

 

You'll also no longer have closed-loop. It's not really a fix, just a band-aid. Whats your car idle at without the BAC plugged in?

 

no closed loop, didn't notice that one... Oh well, it'll be an interesting experiment seeing how the fuel economy is. I don't know for certain on the idle, but it seems that it's about 600 without the bac operating.
It may not be much of a fix... but we'll see how the economy turns out. If it's ok then it really negates the need for anyone to worry about a tps or o2 sensor doesn't it...?

 

Well, the problem with that is, not all cars react the same to not having a TPS, some run just fine, others buck and throw you around. It all varies really. Here's what I suggest. Unplug your bac, start the car and let it warm up and idle, rev it a couple of times and let it fall and see where it settles at (before it slowly climbs back up). If you're under 750, adjust it up using the throttle plate stop screw. The BAC's job isn't to give you a good idle under no loads. Then, adjust your TPS once again, plug in the BAC, plug in the TPS, and give it a try.

 

really??? very interesting, contrary to everything else I'd heard / read. My understanding was mazda designed the idle to be adjusted at the bac, and me adjusting it at the butterfly was a way of lessening the load on a deteriorated bac valve / idle circuit. I'll up the idle to 750 and see how the results are with tps in and out. Thanks.

 

from RETed:
"Either set the TPS correctly or allow the engine to run rich.
It's running like that cause hesitations / surging / jerking is usually an indication of lean conditions.
Check the TPS to see if it's spec.

Yes, the engine will burn more gas.
Hope you can afford the larger gas bill."

The tps is in spec and was new a few years back, it always had an on / off idle buck to it, whether it was the old tps, the new tps, whether it was adjusted properly or not.

 

well the ecu still goes into closed loop, which is interesting...

 

i hate the jerkiness in my car b/c of the TPS!!!!!!

 

I also hate the jerkiness, but here's what's weirder. I adjusted the TPS screw just by the feel of it, since setting to 1kohm by digital multimeter seemed to have no good effect. here's what I did: after I had been driving around for a good while (car warm) I would get out and turn the screw some, then drive again, repeating this until the car would take throttle input at low speed without any humping or bumping. it was PERFECT. I was thrilled.

but now, a couple days later the car is starting to hump and bump again when I modulate the throttle at low speed. the adjustment screw hasn't moved. what else could change and cause the jerkiness? any ideas?

 

sounds like the TPS is failing. I suspect (but have no real proof) that when they start to go from internal build up, that there are dead spots, that don't readily show on even a digital multi meter.

The real proff to that would be is the TPS was replaced with a new one, correctly calibrated for the car, if the problems then went away.

of course the Throttle body mod can also cause the some minor hump/bump jerkyness if you are only lightly using the throttle or trying to modulate low speed/low throttle accell/decel.

 

I haven't done the TB mod to my car... so I can rule that out. I hope it's not the TPS going bad... just one more thing to replace = \

you mentioned "internal buildup"... does that imply that the TPS could be cleaned?

 

yes indeedy, i get that. I cant really drive unless my foot is on the throttle past the point where the TPS is at 100%. Acceleration is woeful.... I do only have secondary injectors though heh.

 

if you adjust the tps by feel, it seems quite likely to me that you'd adjust it to the point where the injectors no longer shut off... doing basically the same thing I've posted about. It's quite clear to me that the tps can cause / affect on off throttle jerkyness even if it's new, I've previously had massive mid throttle hesitations caused by it and replaced it. Wish I'd just unplugged it now.

 

The TPS is a variable resistor, But as far as breaking it open and cleaning it or replacing a worn surface, I don't know. Always just seemed easier to replace it.

 

You can not adjust the TPS "by feel". You will need a multi-meter or Mazda TPS tester (or equivilent).

Anybody working on cars should have a multi-meter in their tool box. It is almost as needed as a set of metric sockets/spanners.

 

ok so is the TPS removal on the plus side or on the down side?

 

if you do not care about gas mileage and afterburn, then it is a plus

 

That was pretty much my point... you *can* adjust it by feel, but you don't end up with the 'correct' (according to mazda) adjustment.

Have you run without the tps for long enough to compare economy Icemark? I'll have a vague result by sometime next week, but won't be too sure until I've put a few tanks through.

 

Nope, I never saw the point of taking something off the car, instead of just fixing it. More so when the broken or questionable part is about the same price as a single decent quality tire.

 

ok, for anyone interested, my economy is the same as ever, fairly reasonable. 14-15L/100km around town.
So in my case, tps removal:

got rid of a failure and adjustment point in the efi system
reduced complexity / underbonnet garbage
made the car drive much smoother on gearchanges and throttle lifts
had no effect on power or fuel economy
increased 'bucking' (afterburn) at low revs with a closed throttle.

 

that's the part that I can't live with.


btw, if anyone has a good s5 TPS for sale let me know