fixed my idle problems, backfiring, bucking and more...
 

For those of you who already know how to adjust your idle and tps, you don't need to read this ... its old news :-)

Ok, I want to be vary careful here because I don't want to get anyone's hopes up that what I did will fix similar conditions in your car, but it may....

Basically my car ran like crap after I got it all back together from the winter updates. I had re-done the hoses, totaly removed double throttle system (except solenoid is plugged in for the ecu), totaly removed AWS, totaly removed fast idle cam and thermalwax rod housing. After my car was back together it had the following problems:

- Idle
idle was really bad, hunted, minibackfires, airpump was coming on at funny times, it stalled a few times, sometimes it would idle high

- Rev sticking
It would stick around 3500-4000 when downrevving, it made it really weird to drive because it would not decelerate right away when you let off the gas, after a few seconds it would eventually go down

- Deceleration backfires
I would get all kinds of backfiring upon deceleration or gear shifting

- Bucking
It would buck when trying to keep a constant speed and buck very bad deceleration.

I know my car is in great shape and had the potential to run perfect so I was determined to get it straight. I did searches here, and on all the normal tech sites and I was able to solve ALL of the issues above and it runs perfect, I mean PERFECT...perfect idle, smooth rev up and down at any load or speed, NO BUCKING and NO BACKFIRING anymore, and proper airpump operation. It is running smoother than when I had all that double throttle/AWS crap on there!!! :-)

The magic egg = TPS!!!!
The throttle position sensor was the key to it all, but it also was the proccess in adjusting the idle in general that I read from a post. This is what I did.

Get all the tools needed to do the TPS adjustment, the details are at the top of this link: http://www.fd3s.net/TPS_adjustment.html

I HIGHLY suggest a digital voltmeter. I got a realy nice one for $14 at radio shack. Make sure it can give you good resolution at 0-14 volt range. (2 decimal maybe)

Before checking the TPS, first set the throttle body to ground zero, what i mean by that is totally close the air adjustment screw that is on the underside of the throttle body, and also adjust the scew on the top of the throttle body so that is does not hold the butterflies open, in other words, so that it just touches the throttle linkage just as the butterflies are fully closed. I got this idea from erics info on this thread: https://www.rx7club.com/forum/showth...threadid=52710

(much thanks to the thread by supercell and great info posted by eric)

Now its TPS time, follow the proccess on the link above, it is a PIA to get to the darn tps screws, but take your time and DONT strip the screws (some new ones may have allen bolts)...mine was WAY off (obviously, by my problems listed above)....but I was able to adjust it to these settings:

Green/Red wire (2nd from top)
Closed = 1.00 V
Open = 4.99 V

Black wire (bottom)
Closed = .4 V
open = 4.3 V

So I got it set just about perfect, and that is exactly how it ran after I started it...well almost. It idled a bit low (500 rpm) so, since I closed the adjustment screws fully, I had plenty of tweaking room. All I did was un-screw the air adjustment (one below throttle body) until I got the idle to 700-800 rpm and that was it.

Drove it all around with a BIG AZZ SMILE on my face....no hunting, perfect idle, no backfiring on decel or shifting. I love it when it all comes together....and this was one of those times.

By the way, my flow mods are catback, DP, and intake...manual boost controllers (running at 9lbs until I get a power FC in here)

Great post, I have many of these symptoms and will definitely try this sometime soon.

thanks gnobesav, good luck and let me know if you need any help..

by the way, I wanted to calrify on the 'bucking'.

there are 2 kinds of bucking people talk about, ignition bucking caused by a messed up idle controls, tps, ISC, et... and the suspention bucking caused by word motormounts, diffmoutns et...

the idle adjustmentsi mentioned above removed all my ignition bucking...however, since my motormounts are definetly broken, I still have a ton of play in the drivetrain, that causes mechanical bucking between decel-accel

you mean jumpiing between 1k and 1.5k rpms?

mine does that, pisses me off

mine does non of that anymore :-)

I'm going to start this project as soon as my friend gets his S14 out of the garage. My symptoms have been a hunting idle at start, and it occasionally stalls immediately after start. Also, I had light-throttle bucking which was fixed by adding extra grounds. The only remaining bucking is from on-throttle to off-throttle. I'll let you know how well it fixes these.

let me know if you need pics or anything

How could the TPS change when you worked on the car damian?

well apparently mine did too

good question, it should not have, however I did have my UIM sent away to be polished and it may have been 'bumped' out of adjustment...also, I removed the AWS, thermal wax rod and cam, and double throttle shaft and butterflies, these changes may have tweaked the idle airflow in some way so that it was off enough to be out of the 'play' range of the TPS.

I have some trouble with my car wich i have explained in a thread a litle bit further down.

But then it couldnt be my TPS since i havent done anything near there.

TobiasRX
post a link to the thread for me...

here it is:

https://www.rx7club.com/forum/showth...hreadid=171137

ahh yess, dunno, ur issues might be non-TPS/idle related?

i have the samething i think . my those that when i hit 2 pounds of boost on the turbo meter gauge. can the cause that too.

yes i dont think it's TPS either since my idle is good.

Had an idle problem of when I reved it it wouldn't slowly settle at 700-800 rpms for idle. It would go all the way down to 300-400 rpms, shutter, then come back up to 700-800 rpms. I tightened the throttle cable and adjusted my dash pot was sticking, got that fixed. It would buck under cruising speed I would eithe rhave to accelerate or decelerate for it not to buck. Put some ground on the car and that went away.

Easy fixes, gotta love'em.

well checked my TPS yesterday since i have the same symptoms...

and found it VERY loose, as in i could swing it by hand with no force...

tonight im going home to adjust it.

interesting huh?

let us know the results tedder1

tedder1, what could have caused your TPS to be loose?

the torque for the scewes is not very much, so it could be possible they just ratteld loose

but it's hardly likely it could have rattled looose when my car just has been sitting though :(

I will look for something tomorrow. thanks for all help and plz post if you come up with something

do this apply to second gens also?

gonna try revving the engine while standing still.

When i drove i couldn't come over 3000 rpm, but i don't know if it's because i pushed the pedal too little.

TobiasRX...are talking about revving while testing the TPS, because you dont need the car on to do that test, just the key in the on position

yes i know damian, i posted in the wrong thread :)

I got a ip about trying to rev my car.

Btw i tried that and i could rev it all the way to redline.

I've discouvered that my problem is probably boost related. When i get boost i get a fuelcut, atleast i think it's a fuel-cut since it's just like the engine stops for a split second, and then when i let go of the gaspedal i get a backfire and it runs again.

Read on my other thread:

"Bump when accelerating"

ahh, yes, maybe fuelcut...but should not be unless your are overboosting?

yes i know, it just feels like a fuel-cut. I really have no clue why it's happening.

i'm having similar problems.. but i'm going to replace the plugs and try out this TPS adjustment, it might be my angel in disguise.

Hey damian,

Just wanted to thank you for pulling all of the throttle stop / air adjust / fast idle adjust / and TPS adjust screws together for me.

My idle is finally where it belongs!

James

James, your welcome.
Great to hear that it helped you get the idle right.

Just did the procedure in the link and it has fixed my back firing problem on start up, between gears and on decel. Easy job, and took less then a hour to do.
Thanks for your help.

glad to hear it helped you too!!!

helped me as well, back when i had a friggin motor in my car

:-)

Damian... do you work at Mazda in milford CT? Just curious, a guy I spoke to there recently told me that my TPS might be the culprit for similiar problems I am having.

Just a silly question. To recalibrate the TPS... the car can be off, but the key in On... and then hook up the volt meter and adjust the screws?

You loosen the screws to adjust the TPS by rotating it slightly until you get the right voltage readings for open and closed throttle.
The screws themselves do not adjust. The car doesn't need to be running as Damian mentioned, just needs ignition on.

heheh, no, i dont work for mazda...maybe i should LOL :-)
Im a computer geek, not a mechanic ;-)

you had the last part right, you can calibrate it with key in on position, with the car not running, hook up vlt meter, loosen screws, adjust tps, tighten screws, recheck voltage again to be sure.

if you have a PowerFC you can also use the voltage reading under the etc menu instead of a voltmeter :)

i read a difference of .2 volts between my radio shack digital meter and the reading on the powerfc.

I took my car out for a drive during lunch today... and had my friend monitor the VTA1 and VTA2 voltages on the PFC while I put the pedal all the way down...

VTA1 read from ~ .4 - 3.8
VTA2 read from ~ 1.14 - 4.97

So it's looking like VTA1 is off by almost 1 volt! That certainly could be contributing to some problems ... whether or not it will fix them remains to be seen.

I read through the tech doc at scuderiaciriani.com on the TPS adjustment. However, it just mentions that if all 4 voltages aren't withing range... rotate the whole unit.

How do I adjust the top end voltage for full range (VTA1) so that it will not get stuck at ~3.8v?

i would first make sure that your actually opening the throttle all the way at WOT, maybe its not actually opening all the way because of a mal-adjusted throttle wire, pedal, or something. Then I would start adjusting the TPS after you verify the throttle is actually opening all the way.

I gave this another test at home. I turned the key to ON after the car warmed up (but engine off), and pushed the pedal as far as I could... and the reading for VTA1 wouldn't go past ~3.8v... while VTA2 made it up around ~4.8. If the cable wasn't adjusted right, wouldn't that effect both readings? Just wondering. Is it abnormal for only one range to be off?

Damian - Do you have a pic of the TPS? Also does the TPS effect the air fuel mixture (i.e. lean vs. rich)? Thanks in advance for your help on this.

Richard.

sorry dont have a pic of the tps, and I dunno how much it affects afr?

hmm, dunno on this one, i think you can just tune it to one of voltage settings, I just cant remember what one is the important one (hehhee)

Thanks for the thread damian, I adjusted my TPS last night as well as my idle screws and I now have the perfect 750 rpm smooth idle, which is a HUGE improvement from what used to be an idle that would hunt between 900 and 1400 rpms. It's also helped out my shifting some, my green/red wire that was supposed to be at like 1.0 V when closed was at 1.8 V so I think it was applying partial throttle at all times making my shifting more difficult.

Yeah, mine used to do that classic signs of a TPS problem. Great writeup!

good to hear you got it fixed up :-)

I got to try this< I've been having problems even starting the car since starting my conversion, and idle was rough getting worse and then no start, will check TPS!


BTW I had my UIM powder coated

Later Days