Rough idle?

[dichiee]

My car idles above 1500rpm for about 5 secs when I'm on a stop and drops to 800-900 area after that. How can I have a smooth idle?

A bmw shop just fixed some hoses and new sparks but it still idles like that.

Any idea?

[kowalski]

is it flashing the engine light at all? have you tried the self diadnostics, turn the key and press the gas pedal 5 times i think it is and it should flash some codes.
is your a/c button on? thats supposed to bump it from 600 up to 800 to run the compressor. what are some other symptoms of this rough idle?

[dichiee]

No there's no flashing CEL.

Ok here's something weird. On my way home I left the A/C and (what do you call that button beside it) on and the RPM drops down straight to 800ish everytime I go to a stop (downshifting or even in neutral). For some reason the idle is fix when those buttons are on.

What do you guys think?

[dichiee]

If the top button is pressed my idle or rpm is smoother. On neutral it drops straight to 800rpm when its not pressed it drops to 1500+rpm

[jfdublyu]

heat soak it man. or at least try, it only costs $10 for a bottle of techron. mine was very erratic going up to 2100rpm until i did a heat soak and now it idles prefect. like magic!

[dichiee]

How exactly do I do this?

[jfdublyu]

the idea is simple. you take concetrated fuel system cleaner (i.e. Chevron techron for up to 20 gal of gas), suck it into the engine using a disconnected vaccuum line and let it sit for at least an hour allowing the cleaner to eat at carbon deposits. the reason why this works is b/c you may have some valve sticking or blocked fuel injectors. here's a breakdown:

1. Pour cleaner into a shallow bowl
2. find a vaccuum line to disconnect. I used the very skinny long one that is connected to the small cylindrical black thing that is just under the AFM.
3. find a partner to help you
4. disconnect the line and plug the open end w/ your finger.
5. have your helper start the car. you should now feel a suction on your finger tip plugging the vaccuum line.
6. have your helper rev the engine to about 2500 rpm and hold it there.
7. quickly place the hose that you are plugging into the bowl of Techron and watch it begin to suck the cleaner up.
8. For optimal results you want to have your partner stall the engine just after all the fluid is sucked up. To do this just make sure that it's in 1st gear w/ the clutch in and after the Techron is sucked wave so they know when to let the clutch out to stall.
9. You will probably begin to see very thick white smoke coming out of exhaust before you cut the car off. this is NORMAL! but it smells kinda bad. don't let your neighbor think your car is on fire! Reconnect whatever line you disconnected
10. Wait at least 1 hr. for the cleaner to really soak eat at the carbon deposits.
11. When you start the car a TON of white smoke should start to pour out of the exhaust as the cleaner continues to be flushed out throught the cylinders. I advise that you find a street somewhere where you can keep moving so that the smoke doesn't build up inside the car and you don't have to breathe it b/c it stinks. when the smoke quits and exhaust looks normal you should be all done! Enjoy the fresh engine smoothness, ahh, drives like brand new!

let me know how it works out for you. i've done this not only on my car but on my Mom's jeep, my friend's turbo Eclipse (gs-t), another friends e30 325i, and a busted honda accord. ALL had favorable results.

[dichiee]

Is this the same as sea foam? If so I just sea foamed the car few weeks ago

[jfdublyu]

yeah, some use sea foam, but i guess i prefer Techron. i get it at Autozone for $10 for the bigger bottle that treats up to 20 gallons of fuel