Regarding "bouncing idle syndrome"

[Dark_Rider2k3]

Noticed that this seems to be a fairly common symptom. I had it before, and searches show a lot of posts about bouncing idles. So here are my tips for fixing this:

1. Check for codes

This was my problem with bouncing idle. I had a bad water thermo sensor, and so once I replaced it all was well! So it's a good idea to check for any codes, as you could have a faulty sensor that needs replaced.

To check for codes on an OBI MX-3:

a) Make sure the car is off, key out of ignition
b) Locate the Diagnostics port inside the engine bay (near firewall on the driver's side.. small black box)
c) Jump the TEN and GND together (paper clip works well for this)
d) turn the key to ON, but do NOT start the engine
e) watch the check engine light. It will flash codes (if any). long holds = 10, short flashes = 1

ex: a code 15 would be 1 long flash, followed by 5 short flashes.

f) if there is more then 1 code, there will be a long pause between flashes. If there is no codes, the light will go away a second or 2 after you turn the key to ON, and never come back.
g) record all codes (for example, when I checked mine I had 2 codes: Code 09, and Code 15)
h) Compare codes with the following:

http://www.mx-3.com/manuals/showimg.php ... F1-075.gif

example: After checking codes, I found that code 09 = Water Thermo-Sensor, and Code 15 = Oxygen Sensor

i) Fix problem using the guide. If you need help search the forums. If you can't find the answer, ask.
j) Reset codes. To reset, disconnect the negative battery terminal and then press and hold the brake pedal for 30 seconds
k) I am not sure how long, but if I remember correctly, you drive for 20 miles or so. Sometimes codes will come back instantly (for example, some sensors when bad instantly throw codes) while others won't immediately.
l) Go back and re-check codes. If no codes appear then congrats!
m) If the same code appears you may have faulty wiring, a new sensor that is bad, or even a bad ECM.


2. Check for vac. leaks

Probably the second most important one to check. Our cars are up there in age, and the hoses won't last forever. To check, just spray brake cleaner around until you hear the RPM's bounce. If you hear them change, the line you sprayed has a crack. Check for it and replace that line. Then see how the idle is.

3. Seafoam the car.

Another cause I've seen is dirty/clogged injectors or even a dirty intake. To use seafoam:

a) use 33% on gas tank with 9-10 gallons of fuel. Cleans fuel injectors, fuel lines, removes moisture from fuel lines. Put it in gas tank at the gas station, then fill it with 9 gallons of fuel, so it can mix well. Just read the bottle for the normal mix ratio.

b) another 33% goes to your crankcase. so open your oil cap and pour it in. *WARNING: It thins out your oil. DRIVE FOR ABOUT 10 MILES, THEN CHANGE YOUR OIL!

c) Rest 33% goes to the intake manifold. It cleans intake valves, cylinder, top of the piston, exhaust valves, etc. To do this, you have to use any vacuum line that goes to the intake manifold.

4. Change your filters.

Especially the fuel filter.

5. Check all ground wires

A loose ground could cause this as well.

6. Check spark plugs, wires, cap, rotor

Not 100% sure on if these could cause a bad idle, but it can cause a the engine to run rough. Still good to check.

7. Adjust your idle

If your idle is very low, even after the other tips, you may want to adjust your idle. I recommend NOT adjusting your idle until you've tried the other tips. I've seen people up their idle, and all that has done is mask their real problem.



And I think that's all I got. If anyone else has tips for fixing a bouncy idle feel free to add!

[PilotSmack89]

FAQ material.

[kakarot135]

agreed FAQ. actually just pulled this up to double check how to clear codes

[resqrandy]

Great write up thanks bro..