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View Full Version : Bouncing Idle issues M20B25


supernaught
02-06-2009, 08:18 PM
This idle is pissing me off a bit.

I've got the car thats for sale, thought I had the idle issue sorted when I replaced the ICV. Smoothed out a little, but still there.

I replaced the plugs, temp sensor and air filter with new, alternator is refurbed(and not draining the batt).

I'm guessing vacuum leak, but so far havent found it.

Starts like a champ and runs higher from cold until it warms up, then rpm bounces from 800-1000. Almost like this, near 800 for 1/2 a second, then 1000 for 1 1/2 secs. and back, repeatedly. If I put on the throttle, it seems to be go up and stay pretty steady. Almost sounds once in a while like its missing.

Fuel: not likely, clean new fuel is in today. Pump seems to keep up okay when revved. Injectors a possibility but i doubt it.
Spark: Just pulled those platinum 2s out and installed proper coppers. Have not replaced wires, rotor or cap yet, although I have new of each on hand.
Air: Newer filter, airbox was clean, AFM seems to flap ok, have not tested it for proper function.
Wiggling vacuum hoses has not proved any improvements. Will look closer tomorrow.
Control: Possible, I replaced the temp sensor and there was no difference, I replaced the ICV and made sure to clean it with contact cleaner(it buzzes as normal) and issue is still there.


Any specific tests I should work on? I've got some ideas to try in the morning, but input is welcome.

richie_s999
02-07-2009, 03:42 AM
Idle control valve, check the hoses going to it,and from it. I had a split in one of my hoses, as soon as I wraped some tape around the split hose it was fine.

it was doing the same thing, start up reving high, theen a 4-600rpm up and down at idle, but drove fine.

T.Dot_E30
02-07-2009, 11:06 AM
Get some car cleaner, spray it around all the hoses and anywhere you suspect it is leaking (Check the intake mani to the head, the gasket could be bad).

If it smoooths out while you are spraying a certain area you found your leak.

FuryriderX
02-07-2009, 12:54 PM
check too the evap purge valve on the bottom of the TB - thats a commonly overlooked spot for a vacuum leak.

supernaught
02-07-2009, 01:15 PM
checking systems now...

supernaught
02-07-2009, 02:24 PM
I'm 3/4 to 90% retarded, just forgot to plug my AFM back in, runs much better. Still a slight waiver here and there, and its a good chance its vacuum. Will be replacing some lines tomorrow so see if it gets better. Overall its waaay better tho.
Thanks guys

everlast
02-08-2009, 12:35 PM
LOL. That's only 65% retarded by the way. :D

supernaught
02-08-2009, 04:25 PM
thanks, it makes me feel better actually.

everlast
02-08-2009, 11:56 PM
:D We all do stuff that like.