One for the experts out there - my '97 XK8 runs great most of the time, but occasionally when it's hot I will lose all power. Sometimes this takes 10-15 minutes of driving, sometimes 1-2 hours. The engine is still running, but the throttle is completely unresponsive, so you slow down using standard physics since the engine is no longer helping you. I'm not getting any OBD codes whatsoever, and the car will run fine again once you let it get completely cool. It's had a new fuel pump and fuel filter, so it's not running out of gas, and since it's still running I would doubt a fuel or spark problem anyway. One ancient post I found suggested replacing the crankshaft position sensor and camshaft position sensor, which changed absolutely nothing. The car has about 69k miles on it, and I did have the ABS module replaced on it (got rid of all the warning lights on the dash).

Any ideas?

 

Next time it happens, use OBD to read as many values as you reasonably can (or can grasp - do some reading!).

Check sensor values for plausibility.

See if it's running CL (closed loop) or OL (open loop).

Check for pending codes.

I take it there are no messages telling you it's in one of its "limp home" or the like modes.

BTW the better OBD tools will let you watch the throttle pedal sensor(s) as you move your foot.

 

I agree with JagV8 on the throttle comment. Two things come to mind,
These are the two most likely causes of your no throttle response.
1) Throttle body (TPS)
2) ECM

While the engine is running but not responsive to throttle input, turn the engine off and start it right back up. Does the throttle respond again or not until it’s cooled off again?

 

Similar thoughts:

• Get a decent OBDII tool (ELM327 and a mobile app) and check both the gas pedal position AND the separate throttle position. From memory, even the older cars have throttle-by-wire, so the 2 numbers are not necessarily the same as when there is a physical cable. With key on, engine off, you can pull the intake tube and visually inspect the throttle position. This might have to be done as the problem occurs unfortunately, but it is good to get a baseline when everything is working ok.
• Early cars are subject to the old capacitor plague of the 90's. Has this ECU ever been rebuilt? If not, it might be good to pull it out and do a visual inspection of the circuit board for those blown capacitors and associated circuit damage. To my knowledge, these can be rebuilt/repaired by reputable providers.
• Something like that happened to me once on another car. Ended up being a broken catalyst ceramic that sometimes lodged itself "sideways" severely impeding exhaust flow. No air out, means no air in, so AFM worked "fine" and there was no code, but no power (engine idled fine, and even allowed me to drive around, but with very low power).
• There is always the possibility that there is a massive air leak that opens up when hot. An OBDII tool would show high short term trims when that happens (unless the engine shuts off I suppose). Triple check the intake tube, especially in the accordion section for hidden cracks.

Best of luck, keep us posted.

 

My 97 has a throttle cable.