Engine Stock TB - smoke test - leaking bad

R82148V · May 18, 2025

Hey everyone,

I have a strange idle issue. when the engine is warmed up it idles good but as soon as you tap the gas or stop at a red light, idle goes up to about 1200 and slowing comes back down under 1000. It’ll usually hunt a little then finally calm down. Did a smoke test and found three areas of a lot of smoke leaking. Egr valve out the vent holes, out the tps and i even have a tps without a hole and the last leak is under the TB at the spring shaft. all three locations was releasing a ton of smoke. TB is stock from 1987. Is this TB toast? would I be able to rebuild the seals or better to just upgrade? I read that they all leak a little but there was a ton of smoke coming out .

gkomo · May 18, 2025

TPS and throttle body just get a new gaskets unless I’m misunderstanding where the smoke is coming from. EGR valve is cheap I would just replace the whole valve.

AeroCoupe · May 18, 2025

If the throttle body is leaking around the shaft I do not believe they are serviceable.

Noobz347 · May 18, 2025

Just about every [used] throttle body you will find out there is 30 ish years old.

It's time to rip off the Bandaid and buy something manufactured in this century.

My personal pick would be Accufab: https://accufabracing.com/product/mustang-5-0l-1986-1993-65mm-throttle-body/

Mustang5L5 · May 19, 2025

Most EGR's will leak. It's technically not a vacuum leak however as it's a positive pressure path. The pintle gets carboned up and creates an uneven seal, so they will alsoo fail the smoke test.

You do want to verify the vacuum diaphragm still holes though. Push the plunger in and put your finger over the vac port and hold. Release the plunger and it should be partially held back by the internal vacuum. Release your finger over the vac port and it should close all the way.

As for smoke leaking out of the seat, try cleaning it up well but don't look for it to seal 100%. Most valves i've tested leak, even new NOS.

R82148V · May 19, 2025

gkomo said:
TPS and throttle body just get a new gaskets unless I’m misunderstanding where the smoke is coming from. EGR valve is cheap I would just replace the whole valve.

smoke was leaking from the TPS and a ton from the throttle spring / shaft underneath the TB. Don't know if this is normal but there is a lot of play in the shaft moving up and down.

R82148V · May 19, 2025

Mustang5L5 said:
Most EGR's will leak. It's technically not a vacuum leak however as it's a positive pressure path. The pintle gets carboned up and creates an uneven seal, so they will alsoo fail the smoke test.

You do want to verify the vacuum diaphragm still holes though. Push the plunger in and put your finger over the vac port and hold. Release the plunger and it should be partially held back by the internal vacuum. Release your finger over the vac port and it should close all the way.

As for smoke leaking out of the seat, try cleaning it up well but don't look for it to seal 100%. Most valves i've tested leak, even new NOS.

I'll definitely check the EGR vac that way a little later today and report back. Didn't know about it being a positive pressure path either. Per the TB leaking smoke from the TPS shaft end and real bad underneath at the spring shaft end, sounds like the TB is shot?

AeroCoupe · May 19, 2025

Yes, with the leak and the shaft moving up and down it would be wise to get a new one.

R82148V · May 19, 2025

looking at the Accufab 65 mm w/ egr spacer. Man they are expensive. I cant find any other manufacturer besides them and BBK.
If going with 65mm, are there any modifications needed to the stock upper intake since the opening is only 60mm I believe?

gkomo · May 19, 2025

There will a step down, which i think is better than a step up, between the TB/EGR to intake opening. Do you need to worry about CARB? I don't know where you live, but i dont think (don't quote me on it) that Accufabs are CARB legal. The BBK ones are though.

R82148V · May 22, 2025

gkomo said:
There will a step down, which i think is better than a step up, between the TB/EGR to intake opening. Do you need to worry about CARB? I don't know where you live, but i dont think (don't quote me on it) that Accufabs are CARB legal. The BBK ones are though.

This is F/I not Carb. I purchased the Accufab 65mm and EGR spacer. Just waiting for it to arrive.
I also just measured the stock upper intake opening and its 63mm for some reason. So is the stock TB at 63mm.
The new TB at 65 being 2mm larger, will it make a difference or "should" I port match the upper intake?

Noobz347 · May 22, 2025

R82148V said:
This is F/I not Carb. I purchased the Accufab 65mm and EGR spacer. Just waiting for it to arrive.
I also just measured the stock upper intake opening and its 63mm for some reason. So is the stock TB at 63mm.
The new TB at 65 being 2mm larger, will it make a difference or "should" I port match the upper intake?

If you have the means, I would just 'blend' the the openings together so that the ramp is smooth.

gkomo · May 22, 2025

R82148V said:
This is F/I not Carb. I purchased the Accufab 65mm and EGR spacer. Just waiting for it to arrive.
I also just measured the stock upper intake opening and its 63mm for some reason. So is the stock TB at 63mm.
The new TB at 65 being 2mm larger, will it make a difference or "should" I port match the upper intake?

I was referring to like SMOG requirements (C.A.R.B.) and just pointing out that i don't believe the Accufabs have a C.A.R.B. #. If you don't need to worry about that then disregard.

Noobz347 · May 22, 2025

gkomo said:
I was referring to like SMOG requirements (C.A.R.B.) and just pointing out that i don't believe the Accufabs have a C.A.R.B. #. If you don't need to worry about that then disregard.

Oil filters don't have CARB exemption numbers either.

Where do you people live that some schmuck at a smog lane is going to know the difference between a stock and aftermarket throttle body?

gkomo · May 22, 2025

Noobz347 said:
Oil filters don't have CARB exemption numbers either.

Where do you people live that some schmuck at a smog lane is going to know the difference between a stock and aftermarket throttle body?

Unfortunately in CA they do notice these things. I had to have a binder of parts i purchased on my last foxbody with printouts of C.A.R.B. numbers matching my car parts just to make life easier because they always asked. There were a few things that i snuck away with just because they are harder to see or at least difficult to see, i.e. i had 24lb injectors and a TFS stage 1 cam, which i believe both are not C.A.R.B. legal. I will say, i did have a ProM 24lb MAF that definitely wasn't C.A.R.B. legal but somehow talked my way out of that one.

Just with my current fox they had the flashlight out extensively checking my JBA headers (which are C.A.R.B. legal). I literally had to go on my phone and show them the C.A.R.B. OE number so they could look it up on their computer system during the test.

Noobz347 · May 22, 2025

gkomo said:
Unfortunately in CA they do notice these things. I had to have a binder of parts i purchased on my last foxbody with printouts of C.A.R.B. numbers matching my car parts just to make life easier because they always asked. There were a few things that i snuck away with just because they are harder to see or at least difficult to see, i.e. i had 24lb injectors and a TFS stage 1 cam, which i believe both are not C.A.R.B. legal. I will say, i did have a ProM 24lb MAF that definitely wasn't C.A.R.B. legal but somehow talked my way out of that one.

Just with my current fox they had the flashlight out extensively checking my JBA headers (which are C.A.R.B. legal). I literally had to go on my phone and show them the C.A.R.B. OE number so they could look it up on their computer system during the test.

It sounds to me like you volunteered information.

If I show up to the lanes with a big beautiful Kenne Bell sitting on the top then yeah... There will probably be questions.

A replacement throttle body??? That clown wouldn't know a throttle body from a carb unless he was a Mustang guy.

It's been a long time but I used to live in Oceanside and then in Carlsbad back the 80s. It was better then. What I drove in HS would never be allowed now. Lol

R82148V · May 22, 2025

Noobz347 said:
Oil filters don't have CARB exemption numbers either.

Where do you people live that some schmuck at a smog lane is going to know the difference between a stock and aftermarket throttle body?

NJ here and they no longer require inspection for any vehicle 25 years or older. Anything 24 years and newer, all they do is plug into your OBD II port and see if you have any trouble codes. Thats it!

gkomo · May 22, 2025

Noobz347 said:
It sounds to me like you volunteered information.

If I show up to the lanes with a big beautiful Kenne Bell sitting on the top then yeah... There will probably be questions.

A replacement throttle body??? That clown wouldn't know a throttle body from a carb unless he was a Mustang guy.

It's been a long time but I used to live in Oceanside and then in Carlsbad back the 80s. It was better then. What I drove in HS would never be allowed now. Lol

I had been through the rodeo enough times to know that bringing the binder makes my life easier, not theirs. They'll fail you even if a part in question is C.A.R.B. legal but you can't 'prove it' on the spot.

Anyways, maybe I just have just gone to 'stricter' SMOG shops unknowingly. Sounds like this guy might not have to worry about that stuff, was just throwing it out there just in case.

I've been in SD for 22 years now, being part of (now defunct) local mustang clubs, we sometimes had 'a guy' at a SMOG shop that would help. But i'm long gone out of that circle now.

R82148V · May 22, 2025

gkomo said:
Unfortunately in CA they do notice these things. I had to have a binder of parts i purchased on my last foxbody with printouts of C.A.R.B. numbers matching my car parts just to make life easier because they always asked. There were a few things that i snuck away with just because they are harder to see or at least difficult to see, i.e. i had 24lb injectors and a TFS stage 1 cam, which i believe both are not C.A.R.B. legal. I will say, i did have a ProM 24lb MAF that definitely wasn't C.A.R.B. legal but somehow talked my way out of that one.

Just with my current fox they had the flashlight out extensively checking my JBA headers (which are C.A.R.B. legal). I literally had to go on my phone and show them the C.A.R.B. OE number so they could look it up on their computer system during the test.

Oh man that's wild!! I never heard of this before!!

Noobz347 · May 22, 2025

Get familiar with "Base Idle Reset" while you're waiting for the delivery guy.

Engine Stock TB - smoke test - leaking bad

Active Member

now i can hopefully expect to receive the shaft

lube between the nut and the face. I know my lubes

Stangnet Facilities Maint Tech... Er... Janitor

That is…until I whipped out my Bissell

Active Member

Active Member

lube between the nut and the face. I know my lubes

Active Member

now i can hopefully expect to receive the shaft

Active Member

Stangnet Facilities Maint Tech... Er... Janitor

now i can hopefully expect to receive the shaft

Stangnet Facilities Maint Tech... Er... Janitor

now i can hopefully expect to receive the shaft

Stangnet Facilities Maint Tech... Er... Janitor

Active Member

now i can hopefully expect to receive the shaft

Active Member

Stangnet Facilities Maint Tech... Er... Janitor

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