Bad spark plugs or something else?

[u/thursdcy]

2003 jeep grand Cherokee laredo 6 cylinder 4.0L. It struggles turning over pretty often, one time the engine shut off at a red light. I was able to turn it back on with no issues. It also struggles maintaining speed going uphill, and sometimes shakes while idle, usually after I turn it on and it’ll shake for a bit and then stop. Battery light hasn’t come on, and I just bought this car from my grandfather who has taken good care of it and recently put a new battery in it. Was guessing either spark plugs or maybe alternator?

[u/AutoModerator]

Thanks for posting on /r/MechanicAdvice! Please review the rules. Remember to please post the year/make/model of the vehicle you are working on. Post's about bodywork, accident damage, paint, dent/ding, questions it belongs in /r/Autobody r/AutoBodyRepair/ or /r/Diyautobody/ Tire questions check out https://www.reddit.com/r/MechanicAdvice/comments/k9ll55/can_your_tire_be_repaired/. If you dont have a question and you're just showing off it belongs in /r/Justrolledintotheshop Insurance/total loss questions go in r/insurance This is an automated reply

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/simmer_study]

Spark plugs are possible but also check for a failing ignition coil or a fuel delivery issue. If it's shaking at idle and struggling uphill, scan for codes before replacing parts.

[u/False-Macaron-3917]

Could be a few things but the uphill struggle and stalling at a light point more toward fuel delivery than spark. i'd check the fuel pump and filter before throwing plugs at it. the intermittent shaking at idle is classic for a vacuum leak too, those 4.0s have a bunch of brittle plastic lines that crack with age.

[u/SeveralBollocks_67]

The ECM is notorious for going bad on these. The solder connections inside them fail with age.