Engine Choking

[redtophb]

I have a 1989 240sx, and I just did a tune up about two months ago; however, when I drive my car between 65-90 mph, my car starts to choke and at times starts to slow down. When my car hits 90+ it drives fine, when it hits 65 or below its fine. Its just at 65-90 that it has some trouble. What could be the problem, and yes I did search.

[DjPantsSpecR]

Engine RPM and transmission will be useful for us to know, so get back with that.

otherwise, coolant temp sensors will go bad, and there will be a significant power loss until around 5300-5500 rpm where power suddenly stacks up.

However, besides some flat spots in the powerband, lower RPM like 1000-3000 rpm power production will seem very similar when comparing a functional and a malfunctional CTS together.

A dyno on fresh alloy proves this, and even shows a loss of 30whp in a spot and a 10 peak whp loss. I can also testify gas milage is around 12 MPG....

but who knows, until you tell us more we cant help too much, but this is a 25 dollar fix, adn can be tested with a ohmmeter...

[redtophb]

Sorry bout that. It's an automatic transmission, and its around I would say 4000 RPMs, but I'll double check on that when I go back home after school. I just realize its around the designated mph, but not RPM. So I will get back to you on the RPM as well. Thanks for the reply.

[redtophb]

I ran my car today and got up to 75 and work my way to 90 mph, just to see what was going on. It turns out that it starts to cough around 3000 - 3500 RPMs, and the speed starts to slow down. I also put it on cruise control at 80 mph and it did the same thing it started to choke. Let me know if you would like me to futher investigate my car to give you more information. Thanks again!

[DjPantsSpecR]

since i dont know exactly what choke means help me out, preferably using a word like bog.

what maintainence have you done on the car. WHen was the last time it got a new air filter, fuel filter, plugs.

does this "choking" happen while you are holding the pedal at a constant angle, or is it on acceleration, deceleration, and any other info.

Only happens at high speeds?

could be a lotta things, send some more info

[redtophb]

I guess you could say it bogs down, sorry for incorrect word usage, and it only happens at high speeds. It usually only happens when its a constant speed. The last time I had my car tuned up was during the third week of January this year. During that tune up I changed the spark plugs, cleaned my air filter, changed oil, and had to change the valve gasket. Before that I don't know when the last time I had a tune up or fixed any prior problems since my dad would take care of the problems. But now that I have it, I'm the one who's doing the tuning up and servicing. Hope this helps, if not I'll tinker around some more. I do appreciate the help!