Annoying hesitation

[tg240sx]

I searched the boards in Infiniti but can find what I'm looking for. I have a 93 J30. Love this car! But I have this annoying hesitation between 1600 and 2000 rpm's. Only noticable when the car is just cruising. Soon as I get over 2000 r's the motor just purr's. Did plugs, wires, fuel rail service with a Motorvac unit, cleaned the MAF, changed the fuel filter, flushed the transmission, put it on the computer, no codes showing. I know that there is probably a shopping list of items to check but I don't know where to start. Any help.

[cweberj30t]

I'm not sure what you mean by the hesitation when you are cruising at 1600-2000 RPM's. Hesitation when you excelerate from there or to there? That whole just cruising thing isn't terribly specific. If you changed your plug wires, I'd say something doesn't check up. Did you mean ignition coils? I would check the throttle bodies and see how dirty the butterfly plates are.

[1qckser]

What did you clean the MAF with? and what brand/ type plug did you use? and did you use a factory fuel filter:) sorry to be a pain.

[tg240sx]

When the car i running at a steady speed, not accelerating or decelerating. Just maintaining a steady speed and the rpm's are between 1600 and 2000. It feels like the motor is misfiring slightly and randomly. I definintly mispoke when I mentioned plug wires. I'm still not used to this car after owning a 240 SX. Used all factory specified parts from Nissan, including the platnum plugs. My mechanic said he cleaned the MAF, with what I'm not sure. i cleaned the butterfly plates with choke cleaner. It went into the shop with the hesitation and came out not changed a bit. The second time it went into the shop we did the fuel rail cleaning. This made an enormous diffrence in the way the car ran and felt. Much smoother but that damn hesitation is still there.

[cweberj30t]

How many miles do you have? It sounds like a timing issue and you may have a loose tensioner. That or Idler Pulley.

[tg240sx]

car has 127,00. timing belt and tensioner has just been repaced

[1qckser]

I hate to beat a dead horse to death, but did you try wiggling the MAF plug, and or was one of the plugs dropped and screwed up the electrode, check for a vacum leaks also.

[Q451990]

Sounds like the Q between 40-45mph in 4th with bad knock sensors... not sure if this holds true for the J or not. More of a hesitation before downshifting.

Heath

[tg240sx]

I gotta rule out the dropped plug because the hesitation existed before the plugs were changed. I'm going to try cleaning every connection i can get to and checking the vaccum hoses soon as i have some coffee.

[Q45tech]

When were the oxygen sensors last changed, sometimes the closed loop to open loop transistion can be like a lean stumble.

What is the amount [duty cycle %] of the IAC at idle?

What is the block learn [% of basic fuel map correction on each bank]...........the O2 can correct +-20% from the ideal as new number].......dirty injectors, dirty TB, deposits on valves, pistions, SMALL vacuum leak, etc..................egr not shutting down fast enough [sticking]..............plus the cam advance solennoids. [noise?].

Tiny problems in transition are sometimes time consumming to find.

[tg240sx]

Since I just bought this car the only service history I have is what we are doing now. I can print this and take it to my mechanic to review. The vehicle was on the computer yesterday but no codes were showing. Need to start to look into this as you suggest. Thanks for the help.

[tg240sx]

Also I cant rule out dirty injectors or deposits on the valves and pistons, but we did do a fuel rail service. Disconnected the fuel system from the car and hooked it up to a Motorvac machine. Ran the car for an hour using chemical cleaning and fuel. This is supposed to remove deposits as you described. The performance of the motor was so greatly improved after this service that I didn't think we were in the same car.

[shai13]

I had the same exact problem with my J30, solution was to spray/clean out both throttle bodies thoroughly and continue to do it every 20-30k.