Saturn Repair: 1995 Saturn SL2 chugging steady speed, mechanic friend, saturn sl2

Question
I drive a 1995 Saturn SL2 with 124000 miles on it.  For the most part, it has been a great car.  However, lately it has been doing this strange chugging thing.  It almost always happens when I'm driving on a highway with the cruise control on, however, it does happen with the cruise off.  It feels like I am suddenly letting off of the gas and giving the peddle a quick punch.  I am assuming that this problem is what is causing my Service Engine light to come on as well since there are no other forseeable problems that it could be.  
I have an ex-mechanic friend with a vehicle diagnostic computer, and upon hooking the computer up to my car it read that my MAP sensor was reading low...so I changed it(about a month ago).  The problem persisted and I was told it could be the TPS, so I changed that too, and again, the problem has still not been solved.  The latest suggestion is that the EGR (linear type) could be the culprit.   I was wondering if there could be any validity to this suggestion or if I should just save my money, and if not, if you have any information that could be helpful to me.  
The car runs great otherwise.  The engine is still very strong and the automatic transmission shifts beautifully, even under high RPMs.  The only time this problem ever really turns up is when the throttle is either steady or under very slight acceleration or deceleration.

Thank you for your time!
Jon

Answer
Jon,

 You most likely have a misfire my friend.  Just one misfire, on one cylinder, on one engine revolution (due to the fact that the Saturn is a 4-cyl) can cause a hiccup.  If you will tell me what codes are in your computer I can better understand the problem.  Your linear EGR valve is designed to be open at highway speeds.  That lets some of the exhaust be re-burned to clean up the emissions.  If it's closed all the time, you will probably see an "EGR Pintle Position Error" come up as a diagnostic trouble code, and your fuel economy will decline.  If it were my car, I would buy some tune-up parts from the Saturn house (you'll only be sorry if you use those Bosch quintuple platinum plugs that the parts stores are so proud of) and give my engine a little TLC.  Hope this helps.

Chris