High Erratic Idle Problem.

urep · 1-26-13, 22:15

OK I have a 93 MX6 2.0L (4 cycl) and the idle will start high at 2000 rpm upon starting and when the cooiing fans kick in it bounces between 1200-1800 rpm.
Occasionally after a stop i.e. engine still warm, I would restart and it would run right (makes me think it;s not a vacuum leak). I've checked for vacuum leaks and found none. I cleaned the IAC as well. So when the car is doing the idle bounce, and the cooling fans are off, I can disconnect the MAF and it will go to a steady high idle (1800 rpms). When the cooling fans come on disconnecting the MAF has no effect and the idle keeps bouncing. Alternatively if I dissconect the IAC the bouncing idle becomes steady whether the cooling fans are on or off. The car is throwing no IBD I code? The MAF has a 3 pronged plug leads (Left-middle-right ) and if I take a volt meter between the left and right leads MAF leads I get a resistance of 4.5Vs. The resistance doesn't change if the car is running or not. Am I measuring the MAF resistance properly? Is this a sign the MAF is bad ; or would the high idle mess up the ohm reading when running?

kentaur · 1-27-13, 14:19

Air bubbles in coolant can cause erratic idle.

urep · 1-28-13, 23:08

Thanks for the response, I have burped the hose lines several times; so I tend to think it is not this. I've been thinking that if the idle is erratic weather the MAF is connected or not, wouldn't this indicate that it's not the MAF?

urep · 1-29-13, 17:31

Just checked again and when I disable the computer, the idle stays high about 1500rpm, but when the cooling fans come on the idle starts to bounce again. Doesn't disabling the computer actually prevent the IAC and MAF units from operating and can I discount these as being the source of my problems? Anyone?

**PaulG** · 1-30-13, 8:09

How did you disable the computer?

urep · 1-30-13, 9:45

I put a jumper wire between GND and TEN on the OBDI Diagnostic connector box.

**PaulG** · 1-31-13, 5:26

That doesn't disable the computer, it just puts it in a TEST or DIAGNOSTIC mode. When you said the resistance was 4.5V for the maf, that's the voltage, not resistance. The resistance is measured in ohms.

A bouncing idle can be caused by a tps that's out of adjustment. It's on the throttle body.