93 300ZX convertible hesitation

[montyz81]

I know this has been discussed in many other forums ad nauseam, but I have not come across a hesitation thread that describes the symptoms of my particular problem. I have a 93 convertible with 54k original miles on it. The car is all original except for the wheels (350z 18-inch wheels). I have a hesitation between 2 and 3k RPM. Here are the details:
The car runs fantastic when cold, with no hesitation in any gears or RPM.
Once the car is warm, the hesitation is in first, second, and third gears.
In first gear, it is a slight blip between 2k and 2500k
In second gear, it is a bit more pronounced above 2500k through about 3k
In third gear, it is very similar to 2nd gear but closer to 3K RPM
In fourth and fifth gear, the car runs normally through the entire rev range.
After 3k in all gears, the car runs normal
I have replaced the fuel filter, spark plugs, and coil packs.
I have cleaned the AFM, Temp sensor, and TPS plugs.
No CEL on the dash, ever.
After driving on the highway (70 - 80MPH), the problem seems to be muted once I get back on the secondary roads
I do not want to cause any issues with the electrical system, so I thought I might post here to see if anyone can help me narrow this down. Diagnostic on an issue like this can run into the thousands because none of the dealerships around me have the Nissan Consult system, nor do they want to spend the time digging into the issue. If I can narrow down a place to start, that would be extremely helpful.
I am sure this is a simple fix; it is just a matter of figuring out the quickest way to determine what is at fault.

Any help would be greatly appreciated.

[montyz81]

Additional information as of yesterday. The temperature here in New England is now in between 50 and 60 degrees. When running my engine from cold, everything works great as I said in my previous post. The funny thing is the hesitation took much longer to show up. It took almost 20 minutes of driving the car for the hesitation to begin. The car usually fully warms up (Temp gauge between 1/3 and 1/2) after about 5-7 minutes (est).

Would this point to the AFM?

Please, I really could use some input on this.

[NolimitZ32]

Sounds like it could be a flat spot in your TPS the only fix for which is a new TPS. Before throwing any parts at it check to see if you have any codes by accessing the ECU. Also read through the troubleshooting section of the FSM (see link in my sig). Nissan of old was smart enough to provide a troubleshooting procedure for most issues to be performed with or without consult. Lastly, if you are not up to the task yourself, find a good specialty shop in your area that has experience with the Z32. No dealer in the US will likely be able to properly work on the Z32 considering most of the techs were born after the model run ended.

[montyz81]

Sounds like it could be a flat spot in your TPS the only fix for which is a new TPS. Before throwing any parts at it check to see if you have any codes by accessing the ECU. Also read through the troubleshooting section of the FSM (see link in my sig). Nissan of old was smart enough to provide a troubleshooting procedure for most issues to be performed with or without consult. Lastly, if you are not up to the task yourself, find a good specialty shop in your area that has experience with the Z32. No dealer in the US will likely be able to properly work on the Z32 considering most of the techs were born after the model run ended.

Thanks for the input. One thing I didn’t mention is, I cleaned the engine bay with gunk before this started to happen. I did try my best to prevent the gunk solvent from getting on any electrical components. Based on what you think it is, I have a few questions. Would a solvent get int the tps to cause issues. I would and did assume I may have gotten it on the TPS connector which I attempted to clean. Next question. Since my car is a 93 and you have a 90 FSM, are there any significant changes that I should think about with regards to fuel delivery and emissions control? I know I have the older 8 bit ECU since the convertibles were based on the 92 MY cars. Thank you again for your input. I’ll try to test the TPS as soon as I can.

[NolimitZ32]

That's a good piece of information to have. Your best bet is to back probe the sensor connectors one by one to find which one is not within spec. There should be an FSM hosted for each year. Btw, they aren't mine, they are published by Nissan and hosted by Nico. As far as your question, the majority of the systems will be identical or almost identical throughout the OBD1 cars.

[montyz81]

Update: Since the weather has gotten cold, the car runs better, and the hesitation takes much longer to show up, even after the engine temp is fully warmed up. Just more information for suggestions.

[NolimitZ32]

Colder weather means longer warm up times, which means colder coolant for longer, so the coolant temp sensor is still a suspect. Is try that first since it's fairly inexpensive, if you don't want to mess with troubleshooting it you could just replace it, it's a fairly simple, cheap, and widely available part. Just make sure you get the two prong one for the ECU and not the single prong that runs the gauge.

[montyz81]

Colder weather means longer warm-up times, which means colder coolant for longer, so the coolant temp sensor is still a suspect. Is try that first since it's fairly inexpensive, if you don't want to mess with troubleshooting it you could just replace it, it's a fairly simple, cheap, and widely available part. Just make sure you get the two-prong one for the ECU and not the single prong that runs the gauge.

Thank you for this. I have a new temp sensor on order. Question: Isn't there a sort of temp sensor in the MAF? I ask as I just took the car out of storage, and the problem has not gone away; however, two nights ago, I drove the car for about 20 minutes with a 10 - 15 minute stop (10 minutes to my destination |10-15 minute stop | 10-minute drive home), and the car ran near flawless. I did not detect any hesitation whatsoever. The outside temp was around 37 degrees Fahrenheit. Yesterday, I drove the car, and the outside temp was around 55 degrees Fahrenheit and the hesitation was back. From past experience, when the outside temp is up in the 80s and 90s, sometimes the car will act like it wants to stall at idle, but it always catches itself. The other interesting part is that the problem does not seem to be getting any worse aside from the fluctuations in the outside temperature range.

I am really not trying to "lead the witness" to the MAF, but really looking to see if anyone can give me a better than 70% chance that the MAF is what is going bad before I bring it to someone. This will help me focus their attention in the right place. This is all in an attempt to limit the diagnosis time charge that a shop would soak me for. Unfortunately, I live in the Northeast (New Hampshire) and there just aren't that many good mechanics that know this car. Nissan basically said they couldn't figure it out and they don't have Consult for ODB1 cars. There is one place (https://northeastautoimports.com/) that can do it, but I know they will charge a ton and are not exactly ZCar specialists. They mostly do JDM GTRs.