1997 Chevy Lumina 3.1 L - Surging Problem

[Kirkwa]

I am hopping some one can point me in the right direction with this problem. Please forgive my lack of proper industry terminology but I will describe the problem the best I can.

When the car is in park and running, it runs a little rough, check engine light is on, and when I press the gas pedal down about a quarter of the way from the floorboard, the engine accelerates and de-accelerates continuously, (surges). The engine does not stall and this does not happen when I am in drive, only when the car is in park or neutral.

I took the car to AutoZone and had them run a computer scan. There were two codes set both were, (PO401 – Exhaust gas recirculation flow insufficient detected in the exhaust gas recirculation system.)

What makes this odd is when the problem first started, per my mechanic’s advice, I had the EGR valve and oxygen censer replace. Unfortunately, this did not fix the problem. I took the car back to the garage and they seem to be at a loss, they could not fix the problem.

The car has 175000 miles to date and the last tune up was done a little over one year ago.

Any help would be appreciated.

Kirkwa

[taillight]

Sometime the passage way to and from the EGR gets blocked with carbon and has to be cleaned out. Sometime the intake manifold has to be removed to do this.

[richtazz]

Checking the EGR feed tube for carbon buildup is very good suggestion. If it appears clear of carbon, a bad vacuum line to the map sensor will cause what you describe as well. The PCM reads the change in vacuum at the MAP sensor when it commands the EGR to open to test it's efficiency. A cracked vacuum line will cause a P0401 code to pop up, even when the EGR is perfectly fine.

[Kirkwa]

Thanks for both suggestions. Question, other than the obvious, visually checking for holes or cracks, can either of you suggest a good way to test for a vacuum leak?

[taillight]

Try spraying carb cleaner on the hose with the engine running. If the speed changes the vacuun pulled the carb cleaner into the leak.