# Stumbling 99 Frontier **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** nissan, frontier\ **Created:** [February 24, 2013, 11:10pm UTC](https://community.cartalk.com/t/stumbling-99-frontier/77590 "2013-02-24T23:10:18Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Samedpaul](https://avatars.discourse-cdn.com/v4/letter/s/6de8d8/32.png) [@Samedpaul](https://community.cartalk.com/u/Samedpaul)\ **Post date:** [February 24, 2013, 11:10pm UTC](https://community.cartalk.com/t/stumbling-99-frontier/77590/1 "2013-02-24T23:10:18Z")
I have a 1999 Nissan Frontier, 4cy, 5speed. About a week ago, it began stumbling sporadically so my first thought was that maybe a spark plug had fouled. I changed the spark plugs, and the problem persisted. At this point, I begin thinking maybe it’s a fuel issue. I went to Advance and bought Lucas Oil fuel system treatment and added it to the 1/2 tank of gas I had at the time. Going home from Advance it ran great. No stumbling. However, it started again the next day. I ran out that 1/2 tank of fuel and filled up again and it is still doing the same thing. It idles a little rough, and stumbles while going up through the RPM range between shifts. Once I get up to highway speed in 5th gear, it seems to do okay. Should I add more fuel injector cleaner or maybe SeaFoam? Could it possibly be a clogged fuel filter? Any advice would be greatly appreciated! ---
**Author:** ![missileman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/missileman/32/1366_2.png) [@missileman](https://community.cartalk.com/u/missileman)\ **Post date:** [February 25, 2013, 3:13am UTC](https://community.cartalk.com/t/stumbling-99-frontier/77590/2 "2013-02-25T03:13:10Z")
I would replace the fuel filter and get the fuel pressure tested before I added any other additive.