Hello everyone. I'm new here to the forum and a new 240SX convertible owner. I'm hoping someone here can help. My apologies if I've broken some rule or ettiquette.

So this is the deal: I bought a 93 convertible off a private owner. It ran and drove fine on the test drive so I bought it. When driving it home, I got 3-4 miles down the road and it stopped responding to the throttle. It slowed from about 45 to 40 mph and stepping harder on it didn't help. At some point, though, the transmission (automatic) downshifted and it started building RPM as if there were molasses in the engine.

Soon after that, it picked up RPM like it was supposed to and the car rocketed to about 90 mph! Well, since it was low on fuel (less than a quarter tank), I stopped at a gas station. I waited for traffic to pass and then I made the left hand turn. Fortunately traffic wasn't all that heavy because stepping on the gas did nothing. It only moved because it has an automatic transmission and my foot was off the brake. I put fuel in it and drove it home with no changes.

So I get it home and over the next week or so, I change the spark plugs (not all that bad), distributor cap and rotor (the rotor showed some signs of wear but wasn't terrible), oil and filter (the oil was dirty), and the fuel and air filter. No change in the performance. A friend of mine told me it likely needed a throttle position sensor since this car is almost 30 years old, has 200,000 miles (for the most part) and probably has mechanical parts to it. I bought one (Beck Arnley) and installed it.

After I installed it, it wouldn't start. I did all the things I thought I was supposed to do but they didn't work. I pulled the spark plugs out, dried them off with a towel and some carb cleaner and left it open overnight to dry. The next morning, I put them back in and the car still wouldn't start. I thought maybe it was getting too much fuel, so I pulled the fuse for the fuel pump. It started for a few seconds and then stopped (no fuel). With the help of a friend, I sprayed some starting fluid in it and it started and ran. I put the fuel pump fuse back in it and it wouldn't start again.

The only thing I had really changed was the TPS and was really careful to line it up correctly and it was a lot of work to install. So, just for shiggles, I unplugged it from the car and plugged the old TPS in. It started and ran with starting fluid. When I stopped the starting fluid and put the fuse back in for the fuel pump, it started and ran. Thinking something might be wrong with the new TPS, I unplugged the old one and plugged the new one back in and it started and ran.

Talk about bizarre!!

It didn't change the throttle sometimes not responding, though. Does anyone have any ideas of what to replace or check next? What could the problem possibly be?

Well, about 3 minutes after I posted this, I got a call from a friend. He told me that he got a call from his friend who used to be a lead mechanic at a local shop and previously had his own shop. He said 99% chance my fuel pump is dying. This is rare because usually fuel pumps work or they don't but for some reason, fighting a dirty filter kills them quicker, especially on these cars. I have ordered another one. I'll let everyone know if it solves the problem or not.

FYI, there is no law that says fuel pumps have to work or not work and I have seen plenty of them give intermittent issues.

A plugged filter kills pump early as the pressure then can deadhead to max, the pump then chews up much faster. No pump on earth likes that.

My '92 had fuel issues when it started getting high on miles. Ran great for years but then got to the point that if it sat longer than overnight, it would start having problems similar to what you described.

I'm no mechanic so this may sound weird, but a can of dry gas would solve the problem until the next time it sat for very long. None-ethanol gas was even better, but more expensive. Apparently the "regular" stuff they make us buy separates if it sits, especially in moderate temps (never seemed to have much problem in high summer, when the outside temps were higher) and my car just would not run without some periodic TLC.

Uh, many forms of dry gas ARE ethanol so if they use ethanol in your local fuel you already have it and silly to pay for it. Read the side of the bottle.

Ethanol fuel separates easier if the humidity is high, but shouldn't on a car with a tight evap system.

Anyone have any other ideas? I installed the new fuel pump, had one bear of a time, got it done and it didn't fix the problem. The man who told me it was the fuel pump on his Mini stopped by. He said I needed to clean the battery terminals (they are clean but look funky because of the protectant spray on them) and should try a compression check. When asked how that would help (it seems like it will have compression or it won't), he had no idea. I don't want to replace the car a piece at a time.

Unfortunately you have a car that is likely way out of tune to mess with your mind. You do a compression check just to verify if the engine is even worth messing with, it tells you whether to waste time on the car or not by revealing the base mechanical condition of the engine. If the engine never will run then there is no sense in messing with it, no tune up parts in the world will fix that--new engine time. Likely not here but you need to know, it tilts diagnosis one way or the other.

You need to run for codes to see what may be telling you is wrong. I do not know how to on that model but if you go up to service manuals at top of page you will find link to get the factory service information on the car and codes and how to get them too.

The thing is, the car runs. It drives, too. After a little while, it stops responding to the throttle. Suddenly, the transmission will downshift and it will rev like it has molasses in the engine for a while. That will clear up all of a sudden and it'll rev to 5 or 6,000 rpm easily. When I slow it a bit, it's back to the same thing. It starts easily and idles smoothly and quietly. I'm about to give up.

Compression check makes sense. It's not "all or nothing," so don't dismiss it.

Unplugging the TPS simply puts the computer in limp mode. It goes to preset values to determine how much fuel to deliver. So, nothing bizarre there.

Have you checked the transmission fluid level properly? Do you know what your battery voltage is at idle? Looking at the battery is useless, and you can't tell if they're good or not, so clean them (that eliminates one more possible issue).

You need to spend some time with a code reader (buy one) and the factory service manual (nissanservicemanual.com).

You bought an unknown, so there's gonna be some effort involved in figuring out why it acts up. If this were easy, this forum wouldn't exist.

X2. The unknown to you thing means you have to start from scratch to weed out all possibilities. On a modern electronic car you verify the basic engine like said (compression), then you go after battery and a loadtest to verify battery power is solid. Then the wiring (main cables to ECM and engine) must be solid to guarantee when you look for codes you get a response that makes sense. Just a low battery can drive you utterly nuts with fake running that seems to change from second to second as the ECM goes insane with insufficient power.

Everybody wants to know the one part that 'fixes it', and why you run for codes now. The problem with electronic cars is that every part being bad on its' own often acts in close to the same way if driven long enough to make a basic running engine go and stay out of whack. Why? Because the part is often not 100% faulty to show up instantly as the issue and then the ECM messes up overall engine tune by chasing the fault while altering other outputs trying to make things work again. The added complication can make for some pretty bizarre running but you have to not freak at that.

Just reread the stream of OP posts, you need to absolutely make sure the battery is up and KNOWN GOOD (loadtest passed) and alt is outputting correctly, a lot of the trouble may just be that. Then on to codes.