I am still battling the issue with my L67 Fiero. The car breaks up/stumbles/bucks/sometimes stalls at around 4k during hard acceleration. Last night while on an HP Tuners logging run I discovered the following:

1. During a hard pull the stumbling occurred as usual. This time when I let off the engine died. It started right back up but I immediately heard vacuum. HP Tuners was flatlining the MAP pressure at this point as well. Popped the deck and found the MAP hose blown off the "T" connector. Hoses are almost new and in great shape with no signs of deterioration. Boost was only measured at 5.8 - could that cause the hose to come off? What could cause this?

2. My ECT goes negative when I apply hard throttle. It will fluctuate dramatically from negative numbers to low positive but does not read the correct range which is normally in the 180 range. Of course the engine now sees this as cold idle mode and activates the idle mode so I get fast idle etc.. I am sure it affects other systems as well as the PCM sees a cold engine. The ECT will eventually go back to normal but I see no pattern other than it fluctuates greatly under hard acceleration. What could cause this - seems unlikely for it to be a sensor that acts up under such defined circumstances.

3. I am not sure about this one, but the TPS % seems to lag the actual throttle position. In looking at the logs I could swear I was more aggressive in applying throttle, and MAP and boost #'s seem to back that up. Is it possible the TPS is mis calibrated?

Have your monitor program going and look at the coolant temp as you wiggle your wires around. You have a bad connection somewhere in the coolant temp circuit. An open in the coolant temp circuit reads -40. So you don't have a total open but you have a high resistance joint. This should be relatively easy to locate as you move wires. The likely suspects - the ECM connector, the CTS connector, and the splice where the CTS connector was spliced on to the harness.

The other possibility is a bad ground - which might explain the TPS error also. The coolant sensor and TPS don't use engine ground, or at least shouldn't. They should be wired back to the ECM for ground.

Since you have positive pressure in your intake manifold it will tend to want to push the MAP hose off. You're going to have to figure a solution to keep the map hose on. Tighter hose, sealant, clamp?

[This message has been edited by phonedawgz (edited 09-22-2010).]