1998 Nissan Frontier Problems Need Some Help

Hello, I have a 1998 Nissan Frontier King Cab XE / 2WD and roughly have 144,000 miles. I experienced a problem about a month ago with my car idling rough and then I was at a traffic light and it stalled on me completely, I had the check engine light come on and battery etc. So I was able to get started up again and it would run. I headed to the Valley to the local Firestone which is about 15 min away I figured if I got on the freeway I was taking a chance but needed to get there quick.

On the freeway it ran perfect. No problems ! I still went to Firestone and when I got it there they managed to put it on the Diagnostics machine. The diagnostics came back with a P)325? Translated to me as a Knock Sensor 1 circuit - the mechanic also said I needed a tune up and the Cap Rotar and wires were erroded and had cracks which lead to the Valve cover needing a new gasket which I was told it leaks in to the spark plug holes. And the did a fuel filter cleaning ( my uncle and I thought we could diagnose it and he replaced the fuel filter before we took it in). Well, he told me the knock sensor was going off because of the problem involving (what I just said above) and that we could get that fixed and go from there.

WELL. After I had the 654.00 work done. It ran great ! I was so happy. Until 4 days later at a light it "whimpered" faintly like a soft pant it wanted to stall but DID NOT this time. I got it home the next day took it back in said I had the work done and it acts the way it was before I had the work done. Wanting to stall. They ran it to see if it would stall and of course it never stalled on them and said "we adjusted the idle" see if that helps and sent me on my way.I told them well I was told that if I got A done B would not happen. They said we cannot get it to stall come back when it is happening.

So here I am it's worse than ever and when I am on the freeway it runs great ! I plan on taking it back and telling them to fix it, they took my 654.00 to get it fixed now its still the same. By the way when it tries to stall I put it in park at the light and run the engine a little so it does not stall ( mainly because we have ninnies that like to beep at you when you have your flashers on - they know what those flashers mean but they HONK) so anyway I noticed a smell not gasoline - that I cannot explain maybe exhaust smell? I did notice a little bit of white exhaust coming from the back of the truck.

Anyone can shed some light on this for me I would appreciate it. Thanks so much. Seeing this is the only car I bought by myself I was lucky enough to buy it out right at the time since my husband passed away at the time leaving me some money to get a new car. So I figured I wont be able to get a new car again like I did the first time around because I cannot afford a car payment. So I thought maybe a new engine or is that just plain silly. Thanks again.

Victoria