[Drews2jzge]

This issue started last week. Was driving home and when I came to a stop, I noticed my rpms did two tiny bounces. like nothing misfire like, but enough to notice that it shouldn't just jump like that. I know about the downshifting, but it doubled jumped. I was weirded out and tried to record it but it literally was fine all day. Fast forward to today. I am driving home from work and this time, instead of fully stopping, it was slowing down and picking speed up again as the light just turned green. just enough to get to a full stop, but then my rpms did the jump thing again. it felt very noticeable and not something my car does. Anyway. As I'm writing this, I have a video of my car where when I started it up to go home from the gym, started it up, idles at 700+-50, foot on the brake pedal still, and I just dropped my e-brake...while in park, my rpms suddenly shot up to 2k rpms. it held it (in the video) even when i took my foot off the brakes. I didn't know what to do so i just put it into gear and...it stopped. I'm home now, but I'm seeing a shop to inspect my car for maintenance...does anyone know what might be happening? I have codes for evap (p0456) and ABS from fuses...

Throttle in parked

youtube.com

 

[Hodgdon Extreme]

Vacuum leak? APPS?

 

[Drews2jzge]

Vacuum leak? APPS?

it doesn't seem to happen at any point while driving and it happened when idling. i went to the shop and they suspect it may be the IAC? my throttle body is used though

 

[MtnBuilt_IS300]

Seems like a brake booster issue or vacuum . How's your braking

 

[Hodgdon Extreme]

it doesn't seem to happen at any point while driving and it happened when idling. i went to the shop and they suspect it may be the IAC?

1. It takes very, very little airflow to increase no-load idle speed from 750rpm to 2000rpm. A tiny intermittent leak could easily cause your rpm fluctuations, while remaining totally unnoticeable at cruising speed.

2. Perhaps try a different (better) shop. These cars do not have an IAC.

 

[Drews2jzge]

Seems like a brake booster issue or vacuum . How's your braking

I performed a brake booster test via the manual that I found on here and it all checks out. The braking works as it should, no stiffness nor anything abnormal

 

[Drews2jzge]

1. It takes very, very little airflow to increase no-load idle speed from 750rpm to 2000rpm. A tiny intermittent leak could easily cause your rpm fluctuations, while remaining totally unnoticeable at cruising speed.

2. Perhaps try a different (better) shop. These cars do not have an IAC.

Gotcha. I have this hose that connects to the too of the intake that has a crack.I made a post about it before and I was told that it was the Air Induction Hose. Would that maybe be something I should look into as well?


I realized that I guess they messed up the terminology of the part, but he was referring to the throttle control module that sits adjacent to the TPS. I apologize for the misunderstanding

 

[AlwaysBroken]

Gotcha. I have this hose that connects to the too of the intake that has a crack.I made a post about it before and I was told that it was the Air Induction Hose. Would that maybe be something I should look into as well?


I realized that I guess they messed up the terminology of the part, but he was referring to the throttle control module that sits adjacent to the TPS. I apologize for the misunderstanding

That’s the vacuum hose connecting to the EVAP system I think. If there’s a crack, there’s a probably leak. And it’s post throttle body so it’s definitely worth it to fix. It could be the problem but I’m pretty sure it’s at least contributing to the problem.

Your brake booster doesn’t sound like it’s leaking in your video and you said you tested it so that is probably fine. When my brake booster was leaking, idle jumps when I stepped on the brakes and a faint hissing sound could be heard.

A throttle body problem should throw some codes regarding APPS or TPS.

And what throttle body control thing? The black round thing sticking out of the throttle body? I mean technically it controls the idle… though a shop calling it a IACV is concerning… It’s like calling a supercharger a bolt on mod.

If that part, the DBW motor, is broken, you’d know about it. Seeing as you didn’t mention the car not accelerating, it’s not going to be the DBW motor. If the APPS is broken, you’d know about it too. Same thing would happen. Simplification but good enough.

 

[Drews2jzge]

That’s the vacuum hose connecting to the EVAP system I think. If there’s a crack, there’s a probably leak. And it’s post throttle body so it’s definitely worth it to fix. It could be the problem but I’m pretty sure it’s at least contributing to the problem.

Your brake booster doesn’t sound like it’s leaking in your video and you said you tested it so that is probably fine. When my brake booster was leaking, idle jumps when I stepped on the brakes and a faint hissing sound could be heard.

A throttle body problem should throw some codes regarding APPS or TPS.

And what throttle body control thing? The black round thing sticking out of the throttle body? I mean technically it controls the idle… though a shop calling it a IACV is concerning… It’s like calling a supercharger a bolt on mod.

If that part, the DBW motor, is broken, you’d know about it. Seeing as you didn’t mention the car not accelerating, it’s not going to be the DBW motor. If the APPS is broken, you’d know about it too. Same thing would happen. Simplification but good enough.

That's what I'm thinking too. the car has had that and I have not addressed it. I should've though, but luckily I'll be seeing them to do my oil change regardless. I do feel a bit concerned about their interpretation of the DBW motor as IAC, but I gave them some slack there. I know these guys through mutual friends and they work on performance cars themselves (I know, that doesn't really mean anything) but they certain aren't the typical run of the mill repair shops that don't know jack crap about cars. I tried my best to explain everything and honestly, I've tried replicating it again about an hour ago after my car sat for a period of time. nothing happened. I really don't know if I'm overthinking it, but I do know that something is happening when it shouldn't.

I will explain more of what I'd like to be inspected on friday.

Also, I've dealt with the notorious throttle problems for nearly over a year. I've made tons of posts about it and recently found out the solution (wire connection) so, I totally get where you're coming from when you say "you'd know about it."

As of the checklist:

1. Mention the vacuum line from the picture again and see if they can repair that
2. Inspect the DBW motor for continuity
3. Fix my horrendous exhaust leak at the bottom of the header -> y-pipe
4. Oil change.

I will update when I get the car there and back!
Thank you for your insights everyone.

 

[Hodgdon Extreme]

Mention the vacuum line

If one hose is cracked, youve got more that are cracked. The rubber on the car is 20 years old. I could literally snap all my evap/purge hoses in half, they were so petrified.

Its a little painful to r&r the intake manifold, but its worth doing to replace all the rubber.

 

[Drews2jzge]

If one hose is cracked, youve got more that are cracked. The rubber on the car is 20 years old. I could literally snap all my evap/purge hoses in half, they were so petrified.

Its a little painful to r&r the intake manifold, but its worth doing to replace all the rubber.

I definitely will say that then. I had my motor replaced a year ago (Nov. 2022) so I never figured out if they swapped over some of the hoses and whatnot. but regardless, I will let them look at all the hoses.