Rough idle, worse MPG, dying at red lights, shaking....

HurricaneJesus · May 1, 2009

I was getting around 23MPG now I'm at around 16. Shaking happens between idle and 2500 RPMs. Doesn't seem to be burning oil. I let a guy look at it and he said it seemed like a bad coil but when he changed said coil, another one would act up, and so forth....Occaisionally the car will shut down and come back on voilently, then I'll get a "CHECK FUEL CAP" error light. I'm also getting a whistling sound at times when I get on the gas.

So far I've cleaned the IAC, MAF, and throttle body, and ran some fuel injector cleaner through the gas tank. It's lessened the problem but not totally eradicated it.

Everything on the engine has 15k on it aside from the intake manifold, TB, MAF, which has 110k.

joshjwc9 · May 1, 2009

First of all, year of the car, and mods done to it?

Pearl02 · May 1, 2009

joshjwc9 said:
First of all, year of the car, and mods done to it?

Along with that, are there any check engine codes? Pearl02.

HurricaneJesus · May 2, 2009

02 GT with 110k, 03 block and heads with roughly 15k
cold air, 75mm TB....think that's about it, engine-wise.

isjoining · May 2, 2009

maybe check and see if you have vacuum leaks?

Jinx · May 2, 2009

This may be dumb... but with 110k on the car and 15k on the engine, are you getting proper fuel pressure at the rails? Could be a partially clogged filter or a fuel pump on its way out. That's the only thing I can think of if the mpg dropped that fast with no recent mods to the engine. Might explain the "fuel cap" message also.

evolucion311 · May 4, 2009

I got the fuel cap message a few summers ago. Then I got a CEL for EVAP Cannister Purge Valve stuck open.

Turns out it was a bad charcoal canister purge valve, which is located in the passenger fender well. It was about $35 from RockAuto and took 10 minutes to swap out.

If the purge valve's function is to inject gasoline fumes into the engine at start up. These fumes are evaporated gasoline from the fuel tank and are collected in the charcoal canister. If the valve is open, it will act just like having a faulty or missing gas tank filler cap: Your gas will evaporate and escape into the atmosphere. Depending on where you live, this may cause your car to fail a smog inspection.

I was evaporating a lot of $ in gasoline until I found this and fixed it. My MPGs rose immediately after swapping the valve.

If you suspect you have a similar problem, don't go to the dealer. At least try swapping the gas tank cap, purge valve, and check all fuel lines inch by inch visually and physically feeling them up with your fingers. The dealer will probably want to put the Rotunda (sp?) smoke machine on your car and charge you $400 in diagnostics and labor to replace a $40 part.

Go ahead and do what you can before the Stealership screws you. Good luck my friend.

HurricaneJesus · May 4, 2009

But my car doesn't smell like gas....so that shouldn't be it, right?

HurricaneJesus · May 26, 2009

Anyone know where to find the purge valve on an '02?

Pearl02 · May 27, 2009

It should be inline with your EVAP cannister. I had to replace the one on my Mazda B4000 last yr. Pearl02.

jivepepper · May 27, 2009

Check for a vacuum leaks like a small hose off around the plenum. Especially the hose on the back of the plenum it goes to the fuel tank. Also look to see if they're just cracked.

Good luck.

agentl074 · May 27, 2009

When my car had rough idle/surging/dying after in gear etc. after I cleaned out my MAS, throttle body...

...they had the PCM reflashed and reset the learning mode. Basically the ASE guys said that the PCM has a set of learning banks for idle mixture etc. and if your MAS was really dirty and you clean it out etc. that it has to adjust for it:

The PCM only adjusts one bank at a time and it needs to go up like five learning banks - just have your PCM learning mode reset and that should do it - if your problem is the same.

squeak93 · May 27, 2009

agentl074 said:
When my car had rough idle/surging/dying after in gear etc. after I cleaned out my MAS, throttle body...

...they had the PCM reflashed and reset the learning mode. Basically the ASE guys said that the PCM has a set of learning banks for idle mixture etc. and if your MAS was really dirty and you clean it out etc. that it has to adjust for it:

The PCM only adjusts one bank at a time and it needs to go up like five learning banks - just have your PCM learning mode reset and that should do it - if your problem is the same.

Are you refering to your Keep Alive Memory (kam)? If so that is reset by simply unhooking your battery for 30 or so minutes (can step on the brake for 30-45 seconds directly after to shorten the wait time).

agentl074 · May 27, 2009

squeak93 said:
Are you refering to your Keep Alive Memory (kam)? If so that is reset by simply unhooking your battery for 30 or so minutes (can step on the brake for 30-45 seconds directly after to shorten the wait time).

Yeah that's it! :SNSign:

squeak93 · May 27, 2009

No need to pay someone for something that you can do with a 1/2 in wrench and a little bit of time...

To the OP.... What did you clean the t/b with?

agentl074 · May 27, 2009

So for future reference ... I just have to unhook the battery, step on the brake for 30 seconds and wait about a half hour? Or unhook battery, wait 30 min, step on break for 30 seconds and drive?

squeak93 · May 28, 2009

agentl074 said:
So for future reference ... I just have to unhook the battery, step on the brake for 30 seconds and wait about a half hour? Or unhook battery, wait 30 min, step on break for 30 seconds and drive?

On my car I only have to unhook the battery and then step right on the brake for 30 or so seconds. What that does it draing the battery reserve for the air bags and kam mem on the puter. usually I'll hook it back up after another minute or two just to ensure I got it all cleared.

agentl074 · May 28, 2009

squeak93 said:
On my car I only have to unhook the battery and then step right on the brake for 30 or so seconds. What that does it draing the battery reserve for the air bags and kam mem on the puter. usually I'll hook it back up after another minute or two just to ensure I got it all cleared.

Cool thanks!

Spreadman · May 28, 2009

It could also be your idle air control motor is going bad. It's located on the front of the upper intake, behind the TB. Mine went bad and had similar symptoms.

bboylobo · May 28, 2009

squeak93 said:
To the OP.... What did you clean the t/b with?

NOS energy drink

Rough idle, worse MPG, dying at red lights, shaking....

HurricaneJesus

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Rough idle, worse MPG, dying at red lights, shaking....

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