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I have a 1987 Nissan Sentra (carbureted California car) with 104,000 miles on it. It generally runs great. However, at idle it is very rough and sometimes stalls. Is the cause the throttle switch? Chilton’s Repair Manual says that the throttle switch monitors engine speed from between 1,000-1,700 RPM.

I would like to be able to answer this question; the bad part is I can't. I don't have enough information to be able to assist you! Here is what I know that you need to do first on this model car with the Hitachi Carburetor. This type carburetor is different than most other types of carburetors out there. In my profession we affectionately call this system the "Hitachi hopeless, chokeless carburetor". The reason we call it by this name is that is does not have a "choke flap" like most carburetors have. It uses input sensors going to the computer to have a fast idle when cold. This is the reason it does not have a "choke flap". The computer monitors the input sensors to control the idle and fuel mixture in the carburetor. Now without you going to the computer and going into the "Diagnostic Mode" to see if any codes are present. I can only tell you what "Most" of the problems we have found over the years with these cars that have idling problems. The single most troublesome problem on this model is "Vacuum Leaks." The biggest “vacuum leak” problem I have found consistently is the hose that comes off of the PCV valve. This will cause a wide range of idling problems that have no apparent cause. To verify that this may be the cause look very closely at ALL vacuum hoses and make sure they are connected properly and not broken. The PCV Valve is just below the carburetor, screwed into the intake manifold pointing towards the firewall. The PCV is completely hidden from the sight by a hose covering it. This hose will be big on one end that covers the PCV and then tapers to a smaller diameter hose that goes to a "vacuum tree". In most cases this hose along with the PCV are clogged up. This hose is a dealer item ONLY! This PCV hose is one of the few parts that are still stocked by dealerships for this older model car. Start with the basics first and see if this helps solve your problem. Let’s not get frustrated with this hopeless chokeless monster from Japan! This is one of the reasons it was used for just 2 years before it was discontinued. It is a system that makes a lot of techs look for a different line of work because it was so frustrating and complicated. Words of caution: DO NOT MAKE ANY EXTERNAL ADJUSTMENTS! If you do make adjustments it MAY open can of worms that will possibly require professional help.

 

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