Throttle position sensor circuit....

[Rick Lee]

Just got my first-ever CEL today. I ran the codes and P1126 came up. Looks like throttle position sensor circuit. Car runs fine, but has had low idle for the last two years, which I had pretty much given up on fixing. Gas mileage has been fine too. I got the CEL while driving after about 45 hwy. miles today. Where do I start repairing this? Thanks.

[kang]

How about the throttle position sensor on the throttle body? It’s a simple potentiometer, and it could easily get corroded. The ECU looks at the resistance at various times and learns what is zero throttle, max throttle, etc. If the resistance is way out of the ball park, it determines that the sensor is out of whack and uses default maps.

[Rick Lee]

I had my lady hold the accelerator pedal to the floor while I poked around the throttle body behind the v-ram. There was still some slack in it. So I guess it could be letting in too much air at idle. I plan to try to adjust it at the pedal first. Looks pretty hard to make any adjustments on the throttle body itself with the engine in the car.

[kang]

I suppose slack in the cable could cause the sensor to produce erroneous readings, but I don’t see how it could cause too much air at idle. Plus, this extra air would increase idle speed, and you say yours is low.

[Rick Lee]

My local wrench says I'm either inducing air upstream from the O2 sensors or an O2 sensor is going bad. I had the right muffler off while doing the plug wires and was thinking maybe I hadn't reseated the clamp well enough. But that's post cat, no? Also, I had the airbox off twice in the last few weeks and am wondering if I left something loose back there.

[JasonAndreas]

Originally posted by kang
I don’t see how it could cause too much air at idle. Plus, this extra air would increase idle speed, and you say yours is low.

If the throttle does not fully return to what the ECU thinks is the zero position then the ISV will not operate, leaving the engine to run only on the air that passes through the partially open throttle-plate. The idle speed won't increase because the ISV is never activated and no air is bypassing the throttle. Rick and several others have had the same (low idle) problem and it's always been after a clutch replacement. During an engine drop you don't need to touch the intake manifold but you do have to disconnect the throttle cable and that is why I suggested it, everything else has been tried and it is the one thing I think they all shared in common. I don't think the P1126 (O2 sensor) fault is related.

[Rick Lee]

Where exactly is the throttle cable section that gets touched in an engine drop? I've done it on a '95, but it was years ago.

[kang]

Originally posted by JasonAndreas
If the throttle does not fully return to what the ECU thinks is the zero position then the ISV will not operate, leaving the engine to run only on the air that passes through the partially open throttle-plate. The idle speed won't increase because the ISV is never activated and no air is bypassing the throttle. Rick and several others have had the same (low idle) problem and it's always been after a clutch replacement. During an engine drop you don't need to touch the intake manifold but you do have to disconnect the throttle cable and that is why I suggested it, everything else has been tried and it is the one thing I think they all shared in common. I don't think the P1126 (O2 sensor) fault is related.

That makes sense. Perhaps that's why he has a TPS error code.