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Engine lights and Idle Surges

Need some help/info. w/ two issues: I own a 2001 Jeep Cherokee Sport, mint. It has about 104,00 miles on it. I am the second owner.

1) About a week ago the “check engine” light appeared after putting some BP regular gasoline in the tank. I took the car to AutoZone to get a reading and it came back as a loose gas cap. I forgot to ask them for the actual code…anyway, I thought it may’ve been put on a bit cock-eyed when I checked it, so I tightened the cap, drove away. I figured I’s give it 4-5 days but to no avail. It’s still on.

2) (I’m wondering if this may be related.) I’m now noticing that I get idle surges when stopped at a light/idling, and as I’m pulling my foot off the gas pedal when preparing to stop. It’s as if the car is getting a small burst of fuel. The RPM’s go from about 1000 to 1500-2000 (Nothing major), but it’s happening every 7-8 seconds or so.

I’m thinking fuel injector, fuel pump, maybe dirty throttle problem??? And what’s up with the loose gas cap reading? Maybe a leak or vacuum issue?

Any thoughts fellow car people? Any and all feedback would be much appreciated!

Oh, I should mention that this “surging” happens mostly during short city trips. When I get above 10 MPH, there aren’t any shifting or surging issues at all and she runs fine.

Surging idle is often related to a vacuum leak. Since this coincided with a loose gas cap code, I would start looking for the vacuum leak in the vapor control system. Disconnect the vacuum hose that goes to the vapor canister (usually hidden in the front left corner somewhere, but on my car it is under the spare tire) and cover the hole in the manifold with your finger to see if the idle smooths out.

I agree. This sounds like a vacuum leak. Another possibility is a dirty Idle Air Control valve, but the gas cap code makes me think vacuum leak.

many thanks for the info. it was my hunch, but it’s good to get a 2nd/third opinion.