just wondering if anyone can explain what exactly happens from small amounts of throttle and back to idle... I'm getting a minor lurch, no matter how slow I back off, and am just wondering what the cause could be. Would that be normal for a t2? I wouldn't have thought it would...

Charlie

 

i'm having the same problem w/ acceleration, but only when i tap the throttle. I was told the TPS is usually the cause for it.

 

I think that is the TPS... is the idle lumpy too?

 

I think mine is doing the same thing you describe, but i havenm't gotten around to setting my TPS yet... I did notice that my A/F gauge shows nothing at all at incredibly light throttle though

 

I've just put a new tps in, and set it... you think the setting could be slightly out?

Charlie

 

Arent TPS fairly expensive? like $185 or so. ive got a lumpy idle and a fairly major lurch going from 0% throtle to 1% on both accel and decel. im guessing TPS...

 

My T2 has ALWAYS done that. I have had about 4 different TPS's, and set them numerous times, confirming with my SAFC readings. And it always revs shitty when I am giving it very light throttle. It kinda sucks cuz, if not for any other reasons, my exhaust is loud so when creping though traffic in town, with my loud exhaust it sounds like my car is all messed up. Sounds really choppy like mifiring, and revs very rough. I am use to it and just give it a lil more throttle but a never endong minor prob, nonetheless. I am still quite sure that is TPS related. I wonder if the ser.5 experience this?

 

IT is the TPS, and it is on ALL t2's I have ever been around. You can even put a good, non-lurching tps from an NA on your t2, and it will still respond int eh same way. I got mien to quit by taking the ******* TPS OFF.

 

If I were to set my idle low, then bump it up with a very mild throttle opening, it would appear that this would go away... but what side effects would I suffer, aside from no throttle freeplay? any?

Charlie

 

Share the info, info hog! Seriously no matter what I do I will never have a smooth car under 1200 rpm =/

 

can anyone comment on my whacky idea above??

Charlie

 

yes, please enlighten us. how do you run the engine w/ no TPS ?!?!?! lol wtf?

Troy

 

OK here goes.

WHen I first got this t2 running(bought it blown) i installed a used engine I got in a trade. IT ran and idled well, IT had the little on/off sensation at light throttle you guys describe, just like EVERY other t2 I have ever driven.
The real problem as that I couldnt go WOT past 4k-6k depending on its mood. IT would just cut back a rotor altogether until I dropped below 4k again.
I thought it was a wiring problem, but it turned out to be the TPS. I tried several I had on hand, but the car didnt like any of them very well. Finally, I said **** it, unplugged it, to see what would happen. I had to do some readjusting for idle but the driveability problems went completely away. Plus, the light throttle buck did as well. To this day the car runs fine with no TPS.

There have been other cars, that I have tried to run with no TPS and they didnt seem to like it as well; I dont know if EVERY Car can be done like this, some may be harder than others to make run w/o it, some may not at all, and some may be like mine. Your methods may vary.

 

Won't the engine run a lot richer down low without a tps...??? or have you compensated for that somehow...

Charlie

 

Runs the same according to the shitty autometer a/f...

 

what exactly does the TPS do? how do you "set" it? i know the TPS sends info on how open your throttle is to your ECU but what exactly does it control?

 

ok guys, for anyone interested in getting rid of this stumbling jerking on off throttle business, I finally bothered to experiment with negative throttle freeplay today... ie throttle always *slightly* on. It's made a huge difference, especially in upshift smoothness. I set the tps back to 1k ohm at closed throttle to compensate, my idle is the same 750ish rpm. Only downside I can see so far is a small amount less engine braking, and I assume a small amount of extra fuel consumption. I'll see after a few tanks how much it affects it, hopefully it won't be noticeable...

 

All EFI systems turn the fuel injectors off when the throttle is completely closed. This is to conserve fuel during deceleration and to stop the bucking that usually occurs on a closed throttle with the injectors still firing. Other that this, the narrow-range TPS on FC's has no effect on how much fuel is injected. The second, full-range TPS on S5's is for the electronic OMP, not the EFI.

There are several probable causes for the jerk that occurs then the injectors are turned off and on. The most common is simply a misadjusted TPS. The ECU stops firing the injectors when the TPS says the throttle is completely closed, but if the TPS is out of whack and the throttle is actually slightly open when the injectors are switched on or off, there'll be a jerk because the airflow is higher than it would be if the throttle were actually closed.

But even with a perfectly adjusted TPS, the problem doesn't go away completely. The two most likely causes for this are 15 years of wear means the factory TPS settings are probably no longer ideal; and this was pretty new technology back then so you can't expect flawless performance.

I've found that with patience you can play with the TPS setting to get the smoothest transistion. But that leads to another inherent problem with the FC's TPS: the linkage doesn't seem able to hold a setting for more than a few weeks (probably due to age again). Shaft-mounted TPS's fitted to most other cars don't seem to have this problem, but the linkage associated with out plunger-type TPS's has an adjustment screw that must move with time. Damn annoying...

One thing that people who fit aftermarket ECU's to FC's always notice is the far smoother transistion when getting on and off the throttle. That's what up-to-date electronics and a better TPS design can do.

 

Hm... Maybe I should try just taking mine off. Ive tried everything else to get rid of my hesitations. Plus everything else is ripped off the motor.. hehe.

 

I have small on / off jerks. I just think it's from 14 years of tranny , u -joint, and diff wear. adding a bit of slop.

 

ok nz, so you say the injectors turn off based purely on tps value, right? So my current, slight throttle opening setup is still shutting them off, because I adjusted the tps so without any throttle pedal movement (though still slight throttle, because of the change I made) it's slightly below 1k ohm. That would lead me to believe the stumble I had wasn't to do with the injectors opening and closing, because according to you they'll still be doing that. So the only real difference now should be a slightly open throttle when coasting down hills, but not injecting any fuel, so not causing any economy problems?

Do you know why throttle freeplay is specified in the first place, if all that I've said is the case?

 

So what is throttle free play and where is it specified?

And this: https://www.rx7club.com/forum/attach...&postid=871818 plus the other chart (DIY) in the manual give clues to the tps's workings.

 

Sureshot's quick TPS check (while driving)

This works best with a loud exhaust. Find a flat open road with no traffic.

Cruise along at about 3K rpm is 3rd or 4th. Lift off the throttle.
This should give a fuel cut on both rotors as you back down. The motor is just pumping air.
Very gently pick up just the slightest throttle.
With practice you can hear the rough sound of only #1 rotor getting fuel, while #2 pumps air.
Then adding just a little more throttle, #2 comes on.

You can also do this as you slow down in gear and the throttle is very near, but not quite at idle.
As you lift the throttle you can hear the #2 fuel cut before #1.
When you get down to near 1500RPM fuel comes back on to prevent stalling, so this works best around 3k.

This transition can be jerky, especially if your idle RPM wants to be high.

 

Doesn't the idle mixture play a part? In my experience with tuning Bosch jetronic injected VWs and Honda injection, having too lean or rich an idle mixture makes a bucking tendency with on / off throttle.

 

Hailers... throttle freeplay is specified in the 88 fsm, under 'fuel and emissions control' - 'intake air system' - 'accelerator linkage', as 1-3mm. A pretty normal value for most vehicles as far as I'm aware, I'm just interested if anyone knows a good reason to have the freeplay there... especially since it makes things signifigantly less smooth for me...

88integra... if somehow with 0.1% throttle I've dramatically changed the mixture, then I guess that was my problem. Spose it would have been a good idea to have a look at o2 sensor voltages at idle and throttle cracked open, before I changed it...