View Full Version : problem with oscillating idle

02-28-2010, 01:32 PM
Hopefully someone can help diagnose - Lately - on my SR, I've had a problem with my idle oscillating badly. The car runs like a champ under throttle, but at stoplights, driveway, etc... the idle oscillates from about 1500 to 2000,without fail. I've checked for vacuum leaks and I've cleaned the MAF and idle air. adjustment to the idle screw on the IACV does nothing. Can anyone point me towards something else?

02-28-2010, 02:54 PM
to help with this- it's a blacktop SR. I was told its possible it could be the coolant temp sensor(ECU) acting up. So, to test this I tried to unplug it and get some kind of result..

The car wouldn't start if the sensor was unplugged prior to cranking it. However, if I started the car then unplugged it, it idled fine, about 1100 rpms (normal with my aftermarket intake manifold)..is this any indication of a problem with the sensor?

02-28-2010, 03:14 PM
the idle adjustment screw will do nothing unless you unplug the throttle position sensors, at least that's how it is on the KA

steve shadows
02-28-2010, 06:01 PM
To correctly set the idle on the SR the following must be performed.

1st check your TPS voltage. Make sure at closed your TPS reads .4 - .49 volts.

At WOT make sure the TPS reads 4.0 - 4.5 volts preferred.

Next make sure your base idle screw on the Throttle body is set in a way that the car will idle at 750-850 RPMS without having the TPS plugged in and without having the IACV OPEN or working

Next you can plug back the IACV then you need to set your base timing. Unplug the TPS sensor while the car is runing check your timing with a timing light, make sure it's set to 15 BDTC. Then plug back your TPS.

Next set the IACV by using a screw driver. The idea is to set the IACV screw open enough that when you blip the throttle quickly and higher up into the rpms as it falls back down to idle it doesnt drop off too low. It settles into it's foot print smoothly. You will need to mess around with the idle screw a bit to find the best possible setting.

I have developed this method to create an almost PERFECT Idle whether the car is running open atmosphere BOV, large cams or power fc with fb control etc, doesnt matter. I get rock solid idle on my clients cars. Make sure if you are using a PFC you do not need to unplug the TPS, however you do need to synch your CAS with you PFC map, by setting the whole timing map to 15 degrees and then making sure the CAS also shows 15 degrees at idle and through the rev ranges.


02-28-2010, 08:36 PM
Steve - thanks for the insight. does your idle cure make sense as to a remedy for my problem though? Are you saying this is where I should go given that I've inspected for leaks, cleaned parts, etc?