Question on throttle

[bsupra]

I have a 91 and 89 supra and their both turbos. When I let go off the gas on my 89, the car slows down pretty decent and basically allows me to shift smooth. While on my 91, I let go off the gas and I feel like engine cuting off fuel(its like ENGINE BRAKE really hard) and its really hard for me to shift it smoothly. Anybody has an idea what I am talking about. Thanks

 

[Poodles]

91 is functioning right...

 

[mkiii222]

There's a little breather that allows the throttle plate to stay slightly open for a split second, almost like using the throttle as an extra bypass valve. It kind of leaves the revs hanging for a second or so when you let off the gas.

Sounds like the 91 isn't working properly or they are just adjusted differently. I had mine adjusted out a bit when I bought it, and setting it to hit the little piston/cushion properly gives about the effect you describe on the 89. If it's backed out and not hitting the piston/cushion thing then it gives the effect you describe on the 91.

There should also be a little check valve and filter hanging off the bottom side of the cushion/piston whatever you want to call it.

ed: almost forgot. when adjusting how hard it hit's the cushion (epc/champion call it a 'dashpot') be sure that the throttle plate still closes all the way. the throttle stop is separate from this cushion/dashpot. If I find a pic I'll be sure to post it. People always advise against adjusting these types of things on the throttle, but I've always found they can net you a better 'feeling' throttle response. You just have to triple check that everything still functions properly as adjusting all the screws can cause the throttle to stick in places if you aren't careful.

 

[bsupra]

There's a little breather that allows the throttle plate to stay slightly open for a split second, almost like using the throttle as an extra bypass valve. It kind of leaves the revs hanging for a second or so when you let off the gas.

Sounds like the 91 isn't working properly or they are just adjusted differently. I had mine adjusted out a bit when I bought it, and setting it to hit the little piston/cushion properly gives about the effect you describe on the 89. If it's backed out and not hitting the piston/cushion thing then it gives the effect you describe on the 91.

There should also be a little check valve and filter hanging off the bottom side of the cushion/piston whatever you want to call it.

ed: almost forgot. when adjusting how hard it hit's the cushion (epc/champion call it a 'dashpot') be sure that the throttle plate still closes all the way. the throttle stop is separate from this cushion/dashpot. If I find a pic I'll be sure to post it. People always advise against adjusting these types of things on the throttle, but I've always found they can net you a better 'feeling' throttle response. You just have to triple check that everything still functions properly as adjusting all the screws can cause the throttle to stick in places if you aren't careful.

Thanks. I hope u get a pic posted soon when u get a chance. I am not good at adjusting these things but i will just take a look for right now. Need to find where that breather and that plate. thanks again

 

[Poodles]

Dashpot is there to prevent stalling, not engine braking.

More than likely your TPS is out of adjustment on the 89 so it's not properly engine braking...

 

[mkiii222]

Dashpot is there to prevent stalling, not engine braking.

More than likely your TPS is out of adjustment on the 89 so it's not properly engine braking...

While I agree that it's there for stall prevention, it does make a noticeable difference when it's not adjusted properly or you go from one car that it's adjusted in and one that it's adjusted out.

It should engine brake no matter what. If the TPS was that far out he'd have other problems. The symptoms he described precisely match what happens when you adjust the screw on the dashpot all the way out so it doesn't hit at all, when you let off the gas it instantly drops revs and engine brakes. With the dashpot in, it still engine brakes, but the throttle 'floats' for a second before you feel it and it's a more gradual feeling.

 

[bsupra]

While I agree that it's there for stall prevention, it does make a noticeable difference when it's not adjusted properly or you go from one car that it's adjusted in and one that it's adjusted out.

It should engine brake no matter what. If the TPS was that far out he'd have other problems. The symptoms he described precisely match what happens when you adjust the screw on the dashpot all the way out so it doesn't hit at all, when you let off the gas it instantly drops revs and engine brakes. With the dashpot in, it still engine brakes, but the throttle 'floats' for a second before you feel it and it's a more gradual feeling.

Thanks for the input. Hopefully I can figure out where it is. thanks

 

[bsupra]

Dashpot is there to prevent stalling, not engine braking.

More than likely your TPS is out of adjustment on the 89 so it's not properly engine braking...

My 89 still engine breaks but my 91 engine breaks real hard. Its like when i let go off the gas on my 91, the engine brakes hard and makes the car jerk specially on 1st and 2nd gear (even at slow speed). My 89 engine brakes but smooth just like my 03 tiburon gt.

 

[Poodles]

Sounds like a TPS issue to tell you the truth...

 

[mkiii222]

My 89 engine brakes but smooth just like my 03 tiburon gt.

:aigo: Comparing a Tiburon to a Supra?????? Anyways, just let us know what it ends up being. Who knows, it could be both.

 

[bsupra]

:aigo: Comparing a Tiburon to a Supra?????? Anyways, just let us know what it ends up being. Who knows, it could be both.

no no no. I should have never said tiburon. Lets just say I had a 90 turbo 5 years ago and it drove the same as my 89. Actually, I test drove a couple of supras before and the my 91 is the only one that gave me this issue.

I can still shift it smooth but I have to play with the gas pedal.

 

[mkiii222]

no no no. I should have never said tiburon. Lets just say I had a 90 turbo 5 years ago and it drove the same as my 89. Actually, I test drove a couple of supras before and the my 91 is the only one that gave me this issue.

I can still shift it smooth but I have to play with the gas pedal.

I was just messing with you about the Tiburon. My first car was a Hyundai (not by choice, but it was a good little beater).

Adjust the dashpot and see what happens, if it's still vastly different then pull out a multimeter and adjust the TPS.

 

[Poodles]

Is the throttle acting like an on/off switch? Mine did that when the TPS went bad on mine...

 

[dumbo]

Have you checked for any codes?

Honestly, this is a tough one to figure out without a road test. It's pretty hard to accurately desribe. Hell it could be low compression in one.

Poodles are you considering a dead spot in the TPS?

When you let off the gas, given the throttle plate is fully closed, doesn't all fuel injection cease untill it gets to an idle RPM?

OP, do both cars run properly besides the said problem.

 

[Poodles]

Either dead spot, badly adjusted, or just plain bad (all the resistances in mine where off and it would stick randomly)

 

[supradjza80]

When you let off the gas, given the throttle plate is fully closed, doesn't all fuel injection cease untill it gets to an idle RPM?

Yes there there is supposed to be a fuel cut during engine braking until rpms get down to 1200 per the tsrm. My car comes back on line at ~1500 rpm. The manual shows how to check for the fuel cutting out but does not detail how you adjust it - at least from what I have seen.

 

[bsupra]

I want to try everything that you guys are suggesting but I will still have figure out how to do these adjustments. Thanks for the input guys, keep them coming.

 

[mkiii222]

... but I will still have figure out how to do these adjustments.

The dashpot just requires a flathead screwdriver and a smallish wrench. You just make sure that the assembly still hits the stop on the side closer to the throttle body and adjust the screw that hits the dashpot.

As for the TPS, http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=100 and the next few pages should cover it. You need a multimeter and phillips screwdriver.

 

[rayall01]

Are you SURE it's engine braking? It's remotely possible a dragging rear brake could cause these symptoms.

 

[bsupra]

OK I finally found the problem. It was A SIMPLE BUT MASSIVE LEAK FROM MY EXHAUST MANIFOLD on the rear part of it. I sould have checked that first before everything since it was a common problem for our cars.