hey guys,
I have a 98 monte with the 3.8 engine and 175k miles. About 2 months ago i had the upper/lower plenum gaskets replaced because of coolant leaking in the engine. Things were fine after that. Then a week ago I took a weekend road trip 250 miles each way. On the way home, i was doing about 80mph for 3 solid hours..as soon as i let off the gas to get off my exit ramp the CEL came on. I went to autozone and it was a bad TPS code (i forget the number now). So being a handy guy, yet not car savvy, i bought a new tps and installed it. The next day i got another code, p0401, egr insufficient flow. Now, i'm thinking its too convenient that it popped up in succession like that for both items to go bad, and am now thinking the TPS in fact wasn't bad and the egr may not be either.
I looked at the egr valve and it looked pretty clean. I did a search and saw a similar post about cleaning one of the lines from the throttle body to the egr but was wondering if anyone had other suggestions?

A web search also talked about a possible map sensor. Also mentioned i should check the pcv fopr a bad gasket or broken spring. The gasket and spring seem to be fine.
Thanks!

I should also add that the car seems to run just fine with the CEL on driving both city and highway.

 

Here's the BEST course of action!

Go back to AutoZone and have the Codes read again.
Then, go inside and plug the Reader into the Printer.
The Printer will print-out EACH Code and what to do to Troubleshoot the Code in a Priority Check-List.

You may find-out that the CEL came-on with a Code for Something > triggered by Something Else being at Fault unrelated to the Sensor that sent the Code ... or, even something very simple like a Fuse blown that protects a System.

The gave me a Print-Out when my Monte Coded for Oxygen Sensors when all I needed to do was replace a blown Fuse.
What the heck.
You have to give it a shot.
Just for the step-by-step troubleshooting.