Nissan Repair: nissan maxima engine knock, nissan maxima, optical pickup

Question
Hi, my 1990 Nissan Maxima has been having some stumbling issues around the 1500-2000 rpm range. When I go to accelerate, the car will lurch a few times until it either gets out of the rpm range or I let off the gas. Just recently the problem has migrated below and above the 1500-2000 rpm range. I've been thinking that it could possibly be fouled or worn out spark plugs considering it has 151,000 miles on it. I bought some new ones and am prepared to replace them. If I let the car sit for a while (right after I just get in and start it) it stumbles and knocks and soft thumps are heard from the engine. The timing is then retarded and the rpm's drop and the problem is fixed for the time being. The fuel filter has also been recently replaced if that means anything. Any help would be greatly appreciated.

Answer
Jefferson,

Yes, the car should have a tuneup.  Also, if you use premium fuel and time the engine for the gas it will perform well.  Change the oil to a 5W30 grade to aid in oiling at startup.  That is, the thinner oil will get oil to all the components quicker and that really helps.  Now, if you have not inspected the distributor for oil I would do that too.  Nissan uses an optical pickup and trigger and oil migrates up the shaft and that gets on the optics after the engine warms up and that causes the engine to cut out and miss.