After every Gas fill up...

T

thrasher

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Contributor
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'02 Protege5
I think my car is losing it...

After every time I fill up with gas, my idle will bounce for about 2 minutes. And then the CEL will come on. Let me explain:

  • Drive around all day until gas is getting low.
  • I fill up, replace gas cap, start car.
  • It's idle will bounce from about 0 to 700 over and over. No stalling, but close.
  • I can drive it fine, power is fine and after about 2 minutes it idles normal again.
  • CEL comes on before I get home.
  • P0421 - warm up catalyst below threshold bank 1
  • I clear the CEL, and all is well until next fill up.

2002 P5, manual. I have just replaced coils to fix the random misfires, replaced plugs with NGK V's, cleaned the EGR and the idle solenoid (the one above the TB) Everything is great until I try to leave the gas station.

Any ideas?

Fix Idle
Maybe the EGR needs a better cleaning or replacement?

Fix CEL
Maybe bad first cat? Why only once right after a fill up? It's a warm up code, but the car has been warm for hours.
 
Last edited:
thrasher said:
I think my car is losing it...

After every time I fill up with gas, my idle will bounce for about 2 minutes. And then the CEL will come on. Let me explain:
  • Drive around all day until gas is getting low.
  • I fill up, replace gas cap, start car.
  • It's idle will bounce from about 0 to 700 over and over. No stalling, but close.
  • I can drive it fine, power is fine and after about 2 minutes it idles normal again.
  • CEL comes on before I get home.
  • P0421 - warm up catalyst below threshold bank 1
  • I clear the CEL, and all is well until next fill up.
2002 P5, manual. I have just replaced coils to fix the random misfires, replaced plugs with NGK V's, cleaned the EGR and the idle solenoid (the one above the TB) Everything is great until I try to leave the gas station.

Any ideas?

Fix Idle
Maybe the EGR needs a better cleaning or replacement?

Fix CEL
Maybe bad first cat? Why only once right after a fill up? It's a warm up code, but the car has been warm for hours.
Click to expand...

I would have to go with that your EGR needs to be cleaned really well if not replaced...if you had a bad first cat then your CEL would be on all the time.....
 
i've heard at a mazda dealer the other day that EGRs sometimes have to be changed after 60,000km
 
My EGR was definately sticking before, when I opened it up to clean it. The shaft of the valve had quite a bit of carbon on it. I cleaned it up pretty good, put a little oil on it etc.

Maybe it is still sticking. Just wierd that it only does this after a refill. Seriously, it idles funny immediately after restarting at the gas station. Even if I had filled it with diesel, the bad gas wouldn't even be in the lines yet.

Any recommendations for aquiring a new EGR? I've got 93,000km. Probably time.
 
thrasher said:
Just wierd that it only does this after a refill. Seriously, it idles funny immediately after restarting at the gas station.
Click to expand...

If you stop at half tank (for instance), take off the gas cap, wait 3 minutes (or however long a refill normally takes). and then put the cap back on, does the car do the same thing?

Assuming yes, try replacing the gas cap. You could also get it tested at a smog inspection place but that would probably cost more than a new gas cap. If the gas cap is loose it will throw a CEL, although I wasn't expecting the one you cited, and it probably should have come on immediately.
 
If it ends up being the 1st cat then go with a header that eliminates it with the CEL fix(nonfoulers)
 
i think if it was an egr problem it would happen all the time...not just after a fill up....i say bad gas cap....?
 
do you top off your tank after it is full? if so, then STOP DOING IT

I just love how everyone here is quick to blame the EGR when there is ANY engine problem
 
I've only had the car a month, so I've been running it empty to judge gas mileage.

It does it right after every fill up. 100%. I'll try popping the gas cap off tonight to see if it does this again. I know the gas has nothing to do with it.

Hopefully the 2 items are unrelated. I just wanted to clear up my funny idle and the CEL before I put my header on.
 
look, if you top off the tank it ***** with the evaporative emissions system... and over time it will damage it and cause this s*** to happen because the engine will be running too rich

do NOT leave the gas cap off to drive or start the engine, it may cause a CEL which indicates an evaporative emissions fault

there's one guy on another board that had a problem like this and it turns out his charcoal canister was faulty and became filled with gas only because there was a pinch in a hose!
 
^^^ yup, loose gas cap can cause CEL. i had it happen on road trips with my 94 B3000. Faulty gas cap seal caused it. Go figure.
 
now that i think about it....any chance it could be the spark plugs???? i know they have an intial firing upon startup????? doubtful but an idea ill just throw out there
 
if he's getting the problem only after filling up then how can it be the plugs?
 
Ok, update.

1. The CEL came on today, I hadn't filled up yet. So it is unrelated to the bouncing idle. Must be the 1st cat which will be removed & replaced with a header & non-fowler on the weekend. No problem.

2. I took the gas cap off, then put it back on. No funny idle. It only happens after a complete fill up.

3. I do not top up the tank. I run it empty, then fill up all the way. = bouncing idle for 2 mins.

Keep in mind, there is no loss of power or bogging of any kind. It is not a misfire, the car runs perfect except it nearly stalls at every stop sign for a few blocks.

Sorry guys, I just can't figure this one out on my own. I really appreciate all your suggestions.
 
thrasher said:
3. I do not top up the tank. I run it empty, then fill up all the way. = bouncing idle for 2 mins.

Keep in mind, there is no loss of power or bogging of any kind. It is not a misfire, the car runs perfect except it nearly stalls at every stop sign for a few blocks.
Click to expand...

Some type of dense contaminant in the bottom of the tank? (Denser than gasoline anyway.)

You run the car to empty and "it" is sitting there on the bottom of the tank below the fuel intake. Then you fill up, which stirs "it" up off the bottom and some of "it", whatever "it" is gets sucked into the fuel lines causing your problem. After a few minutes "it" settles out, no more gets sucked in, and everything is hunky dory again.

If that's the problem then if you fill your tank at empty, wait for a few minutes, and then drive off, the problem shouldn't be as severe since most of "it" will have settled before you start driving and so cannot be sucked into the fuel intake.
 
probably not a good idea to run it so low...1/4 of a tank and then fill it up...maybe it is the egr...get the code read..that's going to help a lot!
 
bazooka joe said:
probably not a good idea to run it so low...1/4 of a tank and then fill it up...maybe it is the egr...get the code read..that's going to help a lot!
Click to expand...

My first post indicates it's a P0421 code, which I also confirmed in a follow-up post, is completely unrelated as it comes on intermitently. I think my first cat is going. (to be replaced by header & non-fouler this weekend)

The explanation of the sediment in the gas tank sounds pretty good. It makes sense that after I run it till empty I would be stirring up what's left and that could be temporarily cloging the filter or something.
 
thrasher said:
Ok, update.

1. The CEL came on today, I hadn't filled up yet. So it is unrelated to the bouncing idle. Must be the 1st cat which will be removed & replaced with a header & non-fowler on the weekend. No problem.

2. I took the gas cap off, then put it back on. No funny idle. It only happens after a complete fill up.

3. I do not top up the tank. I run it empty, then fill up all the way. = bouncing idle for 2 mins.

Keep in mind, there is no loss of power or bogging of any kind. It is not a misfire, the car runs perfect except it nearly stalls at every stop sign for a few blocks.

Sorry guys, I just can't figure this one out on my own. I really appreciate all your suggestions.
Click to expand...


I don't think you're understanding what I'm saying here
"topping off the tank" = fill it to the BRIM

if you still don't understand that means, let me elaborate:
you fill the tank till the gun goes click, then you pull the gas gun out halfway and keep squeezing gas in to "get more gas"
 
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