I have a 2002 SLE with 130,000 on it. About 6 months ago, it started to "cough" once in a while when idling and the engine is at operating temperature. It does not throw any codes. It'* kind of hard to explain. It happens when I sit at a light for a while. It idles smooth around 700 rpm'* and then will "cough", quickly drop down to about 400 rpm'*, and then go right back to normal. It reminds me of when a person unexpectedly swallows some water and coughs it back up.
I had a very small amount of antifreeze loss, and I could see it was leaking out by the throttle body. I thought maybe a bit was getting sucked into the engine once in a while causing the sputter. So a couple months ago, I replaced the upper and lower intake gaskets. Since I had it all apart, I put on new plugs, wires, pcv valve, belt, and fuel filter as well. The problem is still there, however.
It'* not that big of a deal to me, just kind of annoying. Any ideas?

Was it doing the same thing prior to all the work you did?

Also, you say that you replaced the upper and lower intake gaskets, but mention nothing about replacing the Upper Intake Manifold itself. Did you do the work yourself? If so, did you look at the UIM to see if it had any issues ala the common UIM failure at the EGR passage by the TB?

Have you read this article in TECHINFO above?

95-03 Upper Intake Failure Information

I knew I'd miss some stuff. Yes, I did replace the intake manifold with a new one. The gaskets and surfaces were fine and I didn't hit the egr stuff either. The only reason I replaced the intake is because I wasn't about to do all the work and find out that was bad. And yes, the car has done the sputter thing since I bought it.

Have you ever had the codes read?

At this point, it will just be a potentially costly shotgun approach unless we have some idea of what we are facing.

You can often get the codes read at a local AutoZone or Advance. If you do, make sure you write down the whole code and any other info you can get. The more info we have, the more likely it is that we can be of some assistance.

I just went up and had the codes read. The only one was a P1028 code saying the coolant temperature was too low.

Hmmm, that doesn't tell us too much now does it?

The car had not warmed up yet when the code was read?

Did you replace the oxygen sensor when you did the other parts? A combination of coolant contamination and the number of miles you have, means that it is quite likely in need of replacement. Just before mine died, when I tried a Borg/Warner as a replacement, it would do something similar to that. It can caused various strange symptoms.

How about throttle body, mass air flow sensor, and idle air control cleaning?

No, the car was warmed up. I think it was an old code from when it was -10 here about a month ago. I did buy a thermostat, but haven't put it in yet. I guess this could be related to one other thing - when I did the gaskets, I took it to have a cooling system flush done and had them get rid of the dexcool. I can't remember what kind they put in, but it'* green and they told me it was the same kind that comes in the new Fords.

I have not replaced the 02 sensor. I have thought about it, but I buy & replace these cars (our commuter or extra vehicle) from my father-in-law approx every 3 years. He travels a lot for work, so he buys a new car, and when it hits 100,000 he trades it off on something else. He'* a complete neat freak and they look brand new when he trades them in. So we just follow him and unless we don't like the car, buy it from him for what they would give him on a trade. The Bonneville was $5500. I don't mind doing some stuff, but this Bonneville has been an unbelievable money pit and I don't want to stick any more into it than I have to.

I did clean the TB, MAF, and IAC when I had everything apart.

Since I am planning on selling this car in about a year and a half, should I just go with the cheapest 02 sensor? Or will that just cause me more problems?

I appreciate what you're saying, but if he wasn't as much of a neat freak with regularly scheduled maintenance, sooner or later that catches up with you. AC/Delco or Denso O2 sensors only. Anything else could very well only last 2 to 3 months. And, I've yet to find a "cheap" O2 sensor.