98 3.8v6 5 speed with 110,000 miles. I baught the car last year, runs great. I only use it to go from home to work aprox. 10 miles. I don't go over 45 mph. Every now and then I take it out on the interstate highway and "stretch it's legs (wheels) and do 70-85 mph for aprox. 3-5 miles. Everytime I do that, the check engine light comes on. After a few days of returning to going from home to work, the check engine light goes off.
Any ideas on why this happens? I don't notice anything wrong, the car runs great.

 

I have this issue as well. The light always goes out before I can get to AutoZone, so I haven't been able to diagnose it, either...

 

My car does something kinda similar. I get a misfire code and an o2 sensor code (the misfire probably knocked out the sensor) every once and awhile and then it goes away. The only way of knowing exactly is to get it scanned. I bought my own scanner off ebay for $30, it doesn't give a lot of details, just the code numbers and the ability to erase them basically. My car gets these codes under certain conditions, not entirely similar to yours. But I would say you need to get it scanned in order to know where to go from there.

 

It's most likely your O2 sensors so check that out.

Or in a worse situation, your TCC is starting to slip at prolonged high speeds.

I also, like DR, have my own scanner on hand at all times. I got mine for 50 bucks that just reads off the code and the problem description associated with it.

 

Thanks for the tips. I do not see this until I have been cruising at highways speeds for >10 mins, so it has not been as big a concern as other issues. Unfortunately, I have a '95 with the ODB1.5, so if I decide to grab a scanner, I'll have to hack the cable to get it to work...

 

Or just scan it with an OBDII hybrid scanner =P

 

I think it's the TCC because the light will come on after doing 50+ for an hour+...but then it goes off after a couple days. But I don't get a code for that. I just get a code for the misfire and o2 sensor. I have the plugs and wires and sensor to replace...I'm just waiting for the freaking weather to warm up and to stop snowing!

 

It's possible but I wouldn't be able to be sure. My TCC is slipping bad enough to come on randomly now but when it first started going out again, it was only on very slow take off, or high speeds (interstate speeds) and was intermittent like the OP described. Just gotta try and catch it before it goes off heh. The car SHOULD store the code however...

 

Hm, is that something that can be fixed or replaced only?

 

You have to replace the torque converter. The clutches (TCC = Torque Converter Clutch) start to slip and it throws a code called Manufacturer Control Transmission but I don't remember the exact code. Eventually the clutches will completely fail and you won't be able to move the car. So far I've managed to do this to TWO stock torque converters =(