Yup, another idle surge thread. This TB is my kid's truck. We got it with about 130k on the clock. 144k on there now. Earlier this year I put in a set of AC-Delco plugs and cleaned the throttle body it was dirty and needed a good degunking. The kid is now reporting that her car sometimes surges from idle. I cleaned the throttle body again today, it was still pretty clean. I sprayed down the IAT in the inlet air plenum prior to the resonator with some MAF sensor cleaner. It has not set any codes lately. A few weeks ago when she first reported the problem I noted that it had set P1133, heated O2 sensor insufficient sensing; P0136, O2 sensor bank 1 sensor 2 low voltage; and P0128, coolant temp below t-stat regulated temp. These codes were all flagged as intermittent. The codes have not returned and there is no CEL. I drove it around for awhile yesterday and today and it pretty well behaved itself. We took the truck out when we went for dinner. When we got back home it started to do a slow surge in the driveway. The engine would step up in speed and do a slow decline back to idle. I have new AC-Delco O2 sensors waiting in the wings if needed but I wanted something more solid to go on before I started throwing parts at it. My scan tool doesn't give any indications on whats going on with the throttle body. No TB command nor feedback. I would think that would be important data to see if the throttle body was moving while at idle. I've watched the trace on the throttle position sensor and it looks unremarkable. I can cycle it, the TPS, within a range of 18% to about 85%. I also searched the forums for previous threads on these symptoms. I found one thread where it was suggested to replace the t-stat regulator and coolant temp sensor due to low coolant temp. When the truck is driving around the coolant ranges from 185F. to about 195F. I'm going to look into the possibility of a vacuum leak and check the intake manifold bolts. Any help out there?