Confusing Issue

[Apexa]

this is an issue that, apparently, no one in the supra world, or turbo world has heard of so far.. that i've run into at least.

My engine has no vacuum or oil leaks of any kind, whatsoever. everything is connected, and hooked up right. but when my TPS is plugged in, i can stand on the gas peddle, and it'll fuel cut at about 2500RPM, it'll climb, drop, climb, drop, etc etc without me letting off the gas at all.
me, and my shop have been trying to figure this mystery out for about a year now, so, if anyone has ANY advice on how to fix this problem, please, help me out

the list of things that have been replaced/installed trying to fix this:
HKS Fuel cut defencer
new, blow off valve (stocker leaked)
all new hoses and vacuum lines
new, tested ECU
and the TPS has been replaced 3 times, due to us thinking they might have given us a faulty one all 3 times.. but they all tested positive, yet, it still won't rev past 2500RPM unless it's unplugged

anyways, thanks in advance for any help

 

[suprra_girl]

have you done a diagnostic yet? this is the simplest first step to take

i had a problem with idle when my car was going and it was a faulty fcd, one of the chips had broken
have you checked the tps in accordance to the manual?

try removing the fcd for now and just run stock to eliminate that possibility

does it blow out black smoke?

good luck

 

[Apexa]

have you done a diagnostic yet? this is the simplest first step to take

i had a problem with idle when my car was going and it was a faulty fcd, one of the chips had broken
have you checked the tps in accordance to the manual?

try removing the fcd for now and just run stock to eliminate that possibility

does it blow out black smoke?

good luck

That's the problem, we've run a diagnostic test.. many times, but it's not throwing any codes, and we've tested and/or replaced every electronical component on the car. I haven't tried removing the FCD, as it didn't make ANY change when we installed it, anyway. and it doesn't blow any smoke of any kind, with or without the TPS plugged in, and if it does blow smoke, it's just a tiny bit of white smoke from sitting for a long period of time.

 

[Allan_MA70]

tryed a different afm?

 

[jetjock]

You need a better shop. That's RPM cut. When the IDL signal remains on and engine speed and airflow increases the ECU judges the throttle to be open. It thinks: "Wtf? How can this be if the IDL contact is still closed?" It's a condition that should never happen so the ECU is programmed to halt injection when it sees it. It turns the fuel back on again when engine speed and airflow drops and the cycle repeats.

The way to simulate this in a normally good running car is to unplug the TPS and jumper IDL and E then raise RPM. It's all in the book. You have the same condition with the TPS plugged in. Sounds like either the TPS is bad or the throttle plate isn't turning it.

Check the circuit by jumpering the diag block with the key on. You should get a code 51 with the gas pedal slightly depressed. It should go away when the pedal is released. If you don't get these indications that's your problem. Or use an ohmmeter across IDL and E on the TPS and be sure the switch in the TPS opens when the throttle is cracked and closes again when the throttle is released.

In other words the IDL input on the ECU must not be grounded when the throttle is off idle. If the ECU sees that it is it'll do exactly what you describe.

 

[Apexa]

tryed a different afm?

Yep.. tried 3 different AFMs, and still no luck...

 

[Apexa]

You need a better shop. That's RPM cut. When the IDL signal remains on and engine speed and airflow increases the ECU judges the throttle to be open. It thinks: "Wtf? How can this be if the IDL contact is still closed?" It's a condition that should never happen so the ECU is programmed to halt injection when it sees this condition. It turns the fuel back on again when the speed and airflow drops and the cycle repeats.

The way to simulate this in a normally good running car is to unplug the TPS and jumper IDL and E then raise RPM. It's all in the book. You have the same condition with the TPS plugged in. Sounds like either the TPS is bad or the throttle plate isn't turning it.

Check the circuit by jumpering the diag block with the key on. You should get a code 51 with the gas pedal slightly depressed. It should go away when the pedal is released.
If you get don't these indications that's your problem. Or use an ohmmeter across IDL and E on the TPS and be sure the switch in the TPS opens when the throttle is cracked and closes again when the throttle is closed.

In other words the IDL input on the ECU must not be grounded when the throttle is off idle. If the ECU sees that it is it'll do exactly what you describe.

Alright, thanks. I'll try it out as soon as I get some time.. and if the problem still remains.. i'll give you an update

 

[jetjock]

Yeah, print that out (all except the part about needing a better shop ) and give it to your electrical guru. I'm sure that's your problem. Might even be there is no mechanical connection between the throttle plate and TPS. That'd be a new one on me though. Anyway, report back. I'd like to know if I was right...especially if you've been fighting this for so long.

 

[Apexa]

Yeah, print that out (all except the part about needing a better shop ) and give it to your electrical guru. I'm sure that's your problem. Might even be there is no mechanical connection between the throttle plate and TPS. That'd be a new one on me though. Anyway, report back. I'd like to know if I was right...especially if you've been fighting this for so long.

we ran all the tests and at the end of the day it turns out all this time, the TPS plate was on backwards
runs like a champ now. :biglaugh:
it was such an obvious overlooked mistake i couldn't even get mad about it, i just laughed for a good 10 minutes haha
thanks for your help, though!

 

[jetjock]

Lol yep, that would do it. Classic RPM cut symptoms. Ah well, stuff happens. Glad you got it figured out and that I was able to help

 

[isnms]

Man I like this thread.

You're fighting an issue, doing all the troubleshooting you can. Then post with problem and steps you have taken. JJ, a treasure trove of information, chimes in with solid information. With new input your are able to resolve the issue and you posted the results. :bigthumb:

I would have suggested the same thing suprra_girl did.

Good job.

 

[suprahero]

Lol yep, that would do it. Classic RPM cut symptoms. Ah well, stuff happens. Glad you got it figured out and that I was able to help

And this man has the audacity to tell me that HE isn't a genius. You sir are in the classic stages of denial...................

All kidding aside, I don't know what we would do without a handful of the guys that we are lucky enough to have on this site. We all know who they are and they know who they are.....................lol

 

[Insidious Surmiser]

tryed a different afm?

that's what i was gonna say... nevermind tho, lol

 

[suprahero]

I think it was the great philosopher Paul Newman who once said " What we have here is a failure to communicate." Most of the time that pertains to our posts when trying to resolve a problem. It's hard to describe a noise, or a certain color smoke, or other problems we may be having. If somehow we do relay our problems into words that someone like JJ or someone else understands, we usually get a very good answer. That's one of the main reasons I like this site so much...............lol


It may not have been Paul Newman that actually said that, but he was around when it was said. For the youngsters it was in the movie Cool Hand Luke...........lol

 

[Apexa]

whoa, thanks. I'm glad I posted my first tech question up to standards
I was scared I was going to get flamed for something or another. :icon_conf

 

[Nick M]

The real value lies in what isnms pointed out: The poster accurately described his problem and what he'd done to try and resolve it. He then reported back what he found even though it was a simple fix. I wish more would do that.

What a difference it makes with the correct description. Fixing cars on the internet is like hunting ducks with a blind fold sometimes.

no one in the supra world, or turbo world has heard of so far..

Well, not really.

 

[Joel W.]

Best thread I have read in a while guys and gals. It's refreshing...

 

[jetjock]

What a difference it makes with the correct description. Fixing cars on the internet is like hunting ducks with a blind fold sometimes.

Man, isn't that the truth. Why some don't understand the value of good communication when asking for help is beyond me. I can't tell you how many posts I ignore because of this even when I know the answer. If it's hard to read, contains excessively bad spelling or grammar, gratuitous profanity, or doesn't give information needed to make an intelligent diagnosis I simply move on. Apexa did it right and got what he deserved.

 

[isnms]

...ducks with a blind fold...

Wouldn't they be easy to hunt :bigun2: ... j/k,
cause, the chickens have hatched and been counted :icon_bigg


Apexa's back is gonna to get sore :drink1:

having fun with smillies too...::w00t::

 

[Grandavi]

reading the final solution reminded me of the last engine rebuild I did where I put the thrust bearings in backwards and it took me a while to figure out why I destroyed the crank.. lol. Simple things that trip you up are the worst. Its why i love these forums. Brainstorming and good folk.