Hi, My 87 GTA with 350 TPI and AT will not idle at the normal 575 RPM but fairly constantly races up to 13 to 1500 rpm. This condition normally occurs after the motor is up to operating temperature can be intermitent. I no longer believe the codes since 13,14,22,33 & 34 since I've replaced most of the sensors. The IAC, TPS, coolant sensor, oxygen sensor and fan relay switch have all been replaced. Still codes 13 & 14 continue to come on. I've checked the throttle body butterflies and they are closed when the idle is up to 1500. I've changed PROMS twice and this made no difference. I have not changed the ECM since the current was tested by TPI and didn't show any defects. I think the MAF is ok since I cleaned it with a spray and codes 33 & 34 disappeared.
At this point I'm out of fresh ideas and I'm wondering if I have a short in the ECM harness or air is finding it's way into the engine from either an intake leak or an external source.
Any ideas?

Thanks,
Laser

 

Have you checked the intake manifold bolts for any loose ones? Or maybe the plenum bolts. My nephews 87 tpi had a loose plenum bolt and that caused havoc, due to the vacuum leak, which is what this sounds like to me. Of course I also replaced all the vacuum tubing as most of it was dry rotted, and not sealing very well. One of my favorite tools is the mighty-vac vacuum pump. Works fantastic for finding vacuum leaks.