Engine Performance problem
2002 Nissan Sentra 4 cyl Front Wheel Drive Automatic 98000 miles
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Helped friend change the head gasket on his sentra after the car overheated. Changed the head gasket, water pump, and thermostat. When we put the head back on and got everything else hooked up the we started the car and it sounded bad. Had a very rough idle and was idling at about 600 rpm. We concluded that the timing was off. We took off the valve cover and sure enough our timing was off. We took the timing chain off the cam sprockets, put the cams in time according to the mating marks on the sprockets, put the crank at TDC on 1 , then put the chain back on the cam sprockets, valve cover back on and so forth. From the mating marks on the crank and cam sprockets it is timed perfect. We start the car up and it idles high at 1200 rpm, the starts to slow down to around 700rpm. its rough and shakes alot. However you give the car a little gas and the engine sounds great, fires on all four, and there is no shaking, just smooth running, let off the gas and the rough idle shaking starts. I have three theories, the EGR is not working right, I have a vacuum leak, or the IAC is not working right. Need some help here please on diagnosis. Oh yeah prior the head gasket change, we had just replaced the plugs, wires, and the fuel pressure regulator.

Hi boldtvillekid,

Did you check the valve clearances?

Is the ignition timing correct?

If IAC is not working right or vacumn leaks, you would not have 700 rpm.

Did you match the timing marks on the chain with the sprocket? Lower chain too?

I have the same problem with my 2000 sentra.

We figured out what was wrong. We didn't change the rubber gromets on the underside of the valve cover that sit on top of the spark plug holes and oil was getting causing the plugs to get wet. They changed the ruber gasket/gromet and put knew plugs in and it ran alot better but the timing was off just a little. So my buddy had some other dude go over there and he jumped the timnig the wrong direction and hasn't been back to help him. The chain is supposed to have two blue marks and one pink one on it. There is only one mark, factor defect I guess. So all we need to know is how many chain links should the chain have on top when the cams and the crank are set at TDC so we can know how much slack to leave or take out when putting the chains back on the sprockets since we are missing two of the marks that should be on the chain.