• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Stopped at red light, engine almost stalls (*Update* LOTS of carbon in throttle body)

Page 2 - Seeking answers? Join the AnandTech community: where nearly half-a-million members share solutions and discuss the latest tech.
Had this problem before on an Accord. Ran great driving around. Damn near stall at a stop.

Turned out to be the engine coolant temp sensor.

I don't even remember what got me to check it out ... probably a diagnostic flow chart in the service manual.
 
throttle body was filthy!

I looked down the throttle body shaft and it's covered w/carbon.

cleaned around the throat w/a toothbrush.
and sprayed/wiped where ever else my finger could reach.

also checked the coil packs/spark plugs for water. all dry.
but LOTS of carbon around the outside of the coil packs. 🙁

put everything back together.

followed the instructions:
turned ignition to ON w/o starting the engine for a min.
turned it back off for a min.
then started the caR.

car immediately stalled 🙁

had to crank a few sec to gert engine to turn over and car started.

now sitting in car for 10min. another 10min and I will do a test drive.
rpm at 1k
 
Last edited:
JEDI said:
throttle body was filthy!

I looked down the throttle body shaft and it's covered w/carbon.

cleaned around the throat w/a toothbrush.
and sprayed/wiped where ever else my finger could reach.

also checked the coil packs/spark plugs for water. all dry.
but LOTS of carbon around the outside of the coil packs. 🙁

put everything back together.

followed the instructions:
turned ignition to ON w/o starting the engine for a min.
turned it back off for a min.
then started the caR.

car immediately stalled 🙁

had to crank a few sec to gert engine to turn over and car started.

now sitting in car for 10min. another 10min and I will do a test drive.
rpm at 1k
Click to expand...

I'm not the most experienced with this kind of thing, but I think this could be a good time to try some throttle body cleaner to clean farther in than you were able to clean yourself. Something like this. Maybe Seafoam?
 
damn it.. just realized that I didn't disconnect the battery b4.

ok.. re-training my car computer all over again. 🙁

-disconnect battery for5 min then reconnected
- followed instructions about turning car on for a min w/o starting, then off for a min
- started car. now going to sit here for 20min.

then a test drive.

edit:
interesting.. after I disconnected the battery, the car idles at 750 rpm like it normally does instead of the 1k (a couple of posts above) when i didn't disconnect the battery.

did a test drive around the block. seems fine.
there's still a very slight sputter when I'm stopped at a red light but waaaaay better than before.
that small sputter doesn't make the car feel like it's going to stall.

will goto the gym (~5miles away) later on. lets see how a few miles feels like.
 
Last edited:
all I read was "carbon carbon carbon".... carbon here, carbon there, carbon everywhere!

You need to replace your PCV valve as it's probably gummed up, causing blowby to leak past your gaskets, depositing carbon everywhere, at least that's what it seems going by your description. Replacement of the PCV will improve fuel economy and prevent oil burning if it's clogged or even restricted.

You may need to increase your oil change interval though @ 200K miles, it's kinda expected.
 
tortillasoup said:
all I read was "carbon carbon carbon".... carbon here, carbon there, carbon everywhere!

You need to replace your PCV valve as it's probably gummed up, causing blowby to leak past your gaskets, depositing carbon everywhere, at least that's what it seems going by your description. Replacement of the PCV will improve fuel economy and prevent oil burning if it's clogged or even restricted.

You may need to increase your oil change interval though @ 200K miles, it's kinda expected.
Click to expand...

holy Christ u gotta take apart a lot of stuff on a MAzda3 to get to pcv value 😱 :
https://www.youtube.com/watch?v=q4vyxOj7Jbs

my car is rated 34mpg hwy.
at 70% hwy/30% city, I'm getting 32mpg at 200k miles.

I have no idea if oil is burning. I get the oil changed every 7k miles (per the manual about being mostly hwy miles) and the oil change guys have never once said I was low on oil.
(and never had a oil light on dash.)
 
Engine sputtering usually happens after cleaning the throttle body because liquid may have gone inside. That usually clears up after the 2nd or 3rd time you turn the car.
If the throttle body was as dirty as you said, you may take apart the throttle body and do some further cleaning. Usually it's 4 bolts holding the throttle body.
If you plan on using sea foam, put half the bottle through your Brake booster line and the rest in your gas tank, I find it more effective than using a fuel system cleaner and cleans the throttle body even further. Just make sure you read the directions on the seafoam bottle carefully. And yes, I would not trust the engine check light, sometimes you may have symptoms without the light on, which is what happened to me with the dirty throttle body in my car.
 
Last edited:
JEDI said:
damn it.. just realized that I didn't disconnect the battery b4.

ok.. re-training my car computer all over again. 🙁

-disconnect battery for5 min then reconnected
- followed instructions about turning car on for a min w/o starting, then off for a min
- started car. now going to sit here for 20min.

then a test drive.

edit:
interesting.. after I disconnected the battery, the car idles at 750 rpm like it normally does instead of the 1k (a couple of posts above) when i didn't disconnect the battery.

did a test drive around the block. seems fine.
there's still a very slight sputter when I'm stopped at a red light but waaaaay better than before.
that small sputter doesn't make the car feel like it's going to stall.

will goto the gym (~5miles away) later on. lets see how a few miles feels like.
Click to expand...

two things.

1) the car is relearning idle.
2) you might have still have some carbon missed.
2a) I'd try to see if theres a way to get seafoam into the tb while the car is running. (check mazda forums to see if anyone has tried it.)
 
JEDI said:
I have no idea if oil is burning. I get the oil changed every 7k miles (per the manual about being mostly hwy miles) and the oil change guys have never once said I was low on oil.
(and never had a oil light on dash.)
Click to expand...

Next time before changing the oil, check the oil level by looking at the dip stick. if the car is burning excessive oil, it will be by the low level line or maybe even lower.
 
comphollic said:
Next time before changing the oil, check the oil level by looking at the dip stick. if the car is burning excessive oil, it will be by the low level line or maybe even lower.
Click to expand...

I checked oil today before starting my throttle body cleaning.
it's been 6k since my last oil change.
dipstick shows it's between the lines
 
michal1980 said:
two things.

1) the car is relearning idle.
Click to expand...

will the rpms fluctuate while re-learning idle?

at 40mph today, rpms fluctuate between 1k and 1.5k when I let go of the gas.

and more strangely, it then stays at 1.5k rpm and my speed stays at 40mph on a level surface while my foot is off the gas pedal.
as if my cruise control was on. 😱 (it's not.)
 
JEDI said:
will the rpms fluctuate while re-learning idle?

at 40mph today, rpms fluctuate between 1k and 1.5k when I let go of the gas.

and more strangely, it then stays at 1.5k rpm and my speed stays at 40mph on a level surface while my foot is off the gas pedal.
as if my cruise control was on. 😱 (it's not.)
Click to expand...

Im no car expert. But that doesn't sound right.

What I meant by relearning idle, is that when your at a stop it might do the rpm fluctuation.
 
JEDI said:
will the rpms fluctuate while re-learning idle?

at 40mph today, rpms fluctuate between 1k and 1.5k when I let go of the gas.

and more strangely, it then stays at 1.5k rpm and my speed stays at 40mph on a level surface while my foot is off the gas pedal.
as if my cruise control was on. 😱 (it's not.)
Click to expand...
Check your idle air control valve, and clean it if it's dirty. You may have to Google where it is in your car, usually is near the throttle body. If it's dirty clean it with throttle body cleaner.
 
You may be right, but doesn't hurt to look. If it doesn't, I would have the brake booster hose suck some sea foam, let it sit, and Rev the heck out of that engine to remove the carbon build up inside. If it's really dirty, A LOT of smoke will come out of the exhaust. Just make sure to change the spark plugs afterwards.
 
be careful with the seafoam... listen for any unusual sounds like squealing or whatnot. I heard exactly that when I put a bit much seafoam into the engine and so I stopped what I was doing and just let the engine idle normally for a while until the noise disappeared. I can't remember if I shut off the engine and waited a bit before restarting it again. You should be aware that there have been some people who have blown rings or bearings and whatnot with seafoam likely because the carbon is what kept the engine together OR because it dislodged a major chunk of carbon much like dislodging a clogged artery, leading to death (of the engine).
 
comphollic said:
Looks like a good product, but it does the same thing as seafoam but costs 3x more.
Click to expand...

I don't think it's quite the same. The 3m kit has three different products which do three different things. 3M is in the business of making seriously good products and released this within the past 10 years. Seafoam has been around unchanged since the days of carburetors. Yes, it's effective for many things, but I wouldn't say that the 3M kit is the same thing as Seafoam.
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top