91 MR2 Non Turbo idles too high

[rdmitch50]

I've got a 91 MR2 non turbo that won't pass smog because it idles too high. It idles at 1100 rpm warm and it's susposed to be down at 750 rpm according to the test center. The idle adjustment screw is turned all the way down. All the hoses have been replaced. New plugs, cap, rotor, and wires. Tried another throttle body, no help. Switched ECU's, no help. Timing is 10 TDC. Tried a new Air Idle Control Valve, same thing. The car runs great, and passes everything else just fine except it simply idles 300 rpm too high. Cleaned up the EGR valve and everything else I could get my hands on. What else can I do? I'm thinking about replacing the timing belt next. Any ideas? Please help. Thanks

[MR2Jedi]

Not timing belt.
Have you tested your throttle position sensor(TPS)?

[rdmitch50]

No, I haven't checked the throttle position sensor. I'll look it up in the shop manual and test it ASAP. Thanks.

[jasonparlane]

hi there everyone
well high idle in a mr2 is due to 3 problems
1 the idle circuit in the throttle position sensor is worn and no longer showing a circuit

2 idle air control valve is gummed up
check by placing 12v on middle pin and earth one of the outside pins this will close or open the roller valve depending on pin connection. when on closed it should fully shut and u shouldnt be able to blow any air past.

3 throttle butterfly not fully shut, remove from inlet manifold and u shouldnt see any light around the outside of valve, but valve should still open and close without being sticky.

4vacuum leak on pipes or gaskets check with a small amount of lpg around gaskets while engines running and see if engine changes tone/speed

5 this ones great a white wire that runs under the coil pack that runs to the engine fuse panel inside engine bay, this wire breaks. im not sure what it does but when brocken it sure does change the idle

6 not too common, the engine temp sensor could be faulty and makes engine run rich

always check for dtc codes
a faulty oxygen sensor will not change idle as it only makes very small changes to fuel mixtures and will send off a fault code when faulty

most of the time high idle is due to the throttle position sensor, only replace with a new unit dont use second hand units and adjust to bgb specs.

this has taken me some time to learn this and hope it helps a lot of u out