My 2001 XK8 convertible was stored for 4-5 months without a battery. A mile or two after re-installing a fully charged battery the Check Engine light came on and subsequently the Restricted Performance message. I cleared the codes and no MIL or RP message for a couple if miles. Parked it over night and the next day the MIL and RP message returned within 1.5 miles. The RP comes and goes. Could the gas be the cause? The codes I read were: P0300, P0301, P0302, P0303, P0304, P1316, P0352, & P1111. Some codes appeared multiple times.

 

IME 4-5 month old gas won't cause any running issues.

Cheers
DD

 

Have you checked the fuel pressure ? Or checked the filter for blockage ?

Z

 

I haven't checked fuel pressure or the fuel filter. These sound like jobs for the shop. I have no fuel pressure gauge and I can't get under the car to remove the fuel filter. I'm not even a shade tree mechanic. I can swap some parts if they're accessible in the engine bay. My dealer's first appointment is 3 weeks out. Oh well, it sat for 4-5 months. It can sit for a few more weeks.

 

Modern fuels with ethanol can both absorb water and separate if unused over a period of time. So, your fuel could contribute to poor running. If you have capacity, adding fresh gas to the tank can help.

 

I barely drove my car for the first ten months of this year. I didn't want the fuel to remain too long so last month I took it for some rides.
I recently added fuel to my car for the first time this year so the fuel I was burning was purchased last year. No problems.
A few months shouldn't be a problem for you but it might depend on the fuel you're using. I only use name brand premium.