Hello, I tried looking for a solution to this problem but have yet to get a concrete answer. I have a 20V silvertop with ITBs in my ae86. What has been happening recently is that while driving when shifting from 1st to 2nd or 2nd to 3rd my RPMs do not drop. Instead, during midshift the RPMs on my sr5 tach go from 4000rpm to about about 4500 rpm without accelerating. I have to immediately brake to bring down the RPMs and properly shift. Any ideas?

What ecu are you running? and is it running correctly (like running rich or not)? Because, that sounds exactly like a carburetor running rich. Quick off throttle and RPMs rise

I have had this a couple of times, once on my daily, Both times it was down to a faulty TPS, one was worn, and the other was just giving a corrupt signal

ogdougynutty wrote:What ecu are you running? and is it running correctly (like running rich or not)? Because, that sounds exactly like a carburetor running rich. Quick off throttle and RPMs rise

Blacktop ECU. Sounds like it's running rich. Prior to this, I was advised tyhat I should upgrade my fuel pump.

ian.stewart wrote:I have had this a couple of times, once on my daily, Both times it was down to a faulty TPS, one was worn, and the other was just giving a corrupt signal

From all the research I have done. I am beginning to think that this might be the cause. Since this is my daily for now, I noticed that it mainly occurs when dealing with driving locally and dealing with minor traffic.

What happens if instead of selecting the next gear, you just knock it
into neutral and coast with no accelerator, brake or clutch ? Will it hold
a 4500rpm idle, or does it slowly drop to some lower value ?

Cheers... jondee86

Curious to hear the answers to Jondee86s questions.

Make sure the throttle isn't sticking.
Make sure the dashpot under and between the two center ITBs is getting a good vacuum source, is operating properly and is adjusted properly.
Inspect and adjust your TPS by the book.

jondee86 wrote:What happens if instead of selecting the next gear, you just knock it
into neutral and coast with no accelerator, brake or clutch ? Will it hold
a 4500rpm idle, or does it slowly drop to some lower value ?

Cheers... jondee86

This happens as well. When I am in traffic, stay on first and just let of the accelerator so I can cruise, the RPMS remain the same or just rise. After doing research, all things point toward the TPS. If you've encountered this before and know of the cause, please let me know. I am going to order a new TPS and see if this solves the issue. I'll keep you guys posted.

Throwing parts at a problem without diagnosis is the expensive way to frustration.
If you suspect the TPS then test the TPS per the FSM.
It is extremely unlikely this is the TPS.
Much more likely a sticky throttle cable, throttle linkage or something similar.

yoshimitsuspeed wrote:Throwing parts at a problem without diagnosis is the expensive way to frustration.
If you suspect the TPS then test the TPS per the FSM.
It is extremely unlikely this is the TPS.
Much more likely a sticky throttle cable, throttle linkage or something similar.

It's funny that you mention the throttle cable. Now that I think about it, when I manually pull on the throttle wire the little red rubber stopper has a lot of play and just moves around. Not to mention that that when I pull the throttle back, the cable slips off the throttle wheel.

jo3ymac wrote:

jondee86 wrote:What happens if instead of selecting the next gear, you just knock it
into neutral and coast with no accelerator, brake or clutch ? Will it hold
a 4500rpm idle, or does it slowly drop to some lower value ?

Cheers... jondee86

This happens as well. When I am in traffic, stay on first and just let of
the accelerator so I can cruise, the RPMS remain the same or just rise.
After doing research, all things point toward the TPS. If you've encountered
this before and know of the cause, please let me know. I am going to order
a new TPS and see if this solves the issue. I'll keep you guys posted.

Just a thought... if the Idle Speed Control Valve (ISCV) is unplugged/stuck
open or otherwise not working, the idle can sit in the 4000-4500rpm region.
Yours sounds like it could be gummed up with accumulated carbon crud. So
it would be a good idea to take it off and give it a clean. Here it is...



Unplug, remove the two rubber hoses, undo two bolts, lay it on the bench
and admire your handiwork. It is in a kind of difficult place, under the ITB's
at the rear of the engine, so you will need a beer

Spray carb cleaner in one tube and it should run out the other tube bringing
out a bunch of black stuff. Keep at it until no more black stuff comes out.
You can recycle the carb cleaner if you catch it in a container and let the
black bits settle to the bottom. You can remove the plastic solenoid to get
at the spindle to check if it rotates easily in either direction. Note that it
does not do a full rotation... just move like a quarter turn each way from
center.

Do not remove the cover on the other end of the spindle. There is a small
bimetallic spring inside, and the cover is factory adjusted and sealed for
correct operation. Don't mess with it.

When the valve is clean and dry, shoot it with a bit of CRC so that it moves
easily, put the solenoid back on and re-install to the engine. When the ISCV
is working correctly, your hot idle should drop and hold steady at 900rpm +/-
when you knock the car out of gear. The idle could be a bit higher if you
have accessories or A/C turned on.

Cheers... jondee86

jondee86 wrote:

jo3ymac wrote:

jondee86 wrote:What happens if instead of selecting the next gear, you just knock it
into neutral and coast with no accelerator, brake or clutch ? Will it hold
a 4500rpm idle, or does it slowly drop to some lower value ?

Cheers... jondee86

This happens as well. When I am in traffic, stay on first and just let of
the accelerator so I can cruise, the RPMS remain the same or just rise.
After doing research, all things point toward the TPS. If you've encountered
this before and know of the cause, please let me know. I am going to order
a new TPS and see if this solves the issue. I'll keep you guys posted.

Just a thought... if the Idle Speed Control Valve (ISCV) is unplugged/stuck
open or otherwise not working, the idle can sit in the 4000-4500rpm region.
Yours sounds like it could be gummed up with accumulated carbon crud. So
it would be a good idea to take it off and give it a clean. Here it is...



Unplug, remove the two rubber hoses, undo two bolts, lay it on the bench
and admire your handiwork. It is in a kind of difficult place, under the ITB's
at the rear of the engine, so you will need a beer

Spray carb cleaner in one tube and it should run out the other tube bringing
out a bunch of black stuff. Keep at it until no more black stuff comes out.
You can recycle the carb cleaner if you catch it in a container and let the
black bits settle to the bottom. You can remove the plastic solenoid to get
at the spindle to check if it rotates easily in either direction. Note that it
does not do a full rotation... just move like a quarter turn each way from
center.

Do not remove the cover on the other end of the spindle. There is a small
bimetallic spring inside, and the cover is factory adjusted and sealed for
correct operation. Don't mess with it.

When the valve is clean and dry, shoot it with a bit of CRC so that it moves
easily, put the solenoid back on and re-install to the engine. When the ISCV
is working correctly, your hot idle should drop and hold steady at 900rpm +/-
when you knock the car out of gear. The idle could be a bit higher if you
have accessories or A/C turned on.

Cheers... jondee86

Thanks for the info, I really appreciate it. My TPS is coming in this week. I will test and see how that works out. If the problem persists, I will try what you've suggested.

Update:

For those of you who are interested in this thread, I recently changed the TPS. For a while I did not experience any high idling. However, the issue has returned. It's not as bad as it was prior to swapping the TPS but the problem still persists. MY next step is to clean the ISCV. Once that is done, I will test it out and see what the results are. I will keep this thread updated and let you guys know what the results are.