My 98 GMC suddenly has a flat spot at 1100 rpm under a very light load: starting off on flat ground. I had a tune up 1.5 years ogo and they did not change the plugs just the rotor cap and plug wires. I just checked the cap and it is clean. The check engine light has been on and the code is the right bank o2 sensor. Could this cause the problem? :banghead:

The truck is in the shop today and I will post the results.

its possible that the sensor going bad is causing it. replace the sensor would be the easiest way to tell. they are pretty cheap and not that hard to replace.

thanks for the input. I did change the plugs but no difference. I will have it checked for codes again.

codes on this problem came up as P404 Exhaust gas recirculation circuit range/performance. P 405 Exhaust gas recirculation sensor A circuit low. The mechanic cleaned the EGR valve and the truck runs fine now but the SEL is still on.

codes on this problem came up as P404 Exhaust gas recirculation circuit range/performance. P 405 Exhaust gas recirculation sensor A circuit low. The mechanic cleaned the EGR valve and the truck runs fine now but the SEL is still on.
you may want to look into adding a oil catch can. the way they send the exhaust gas thru the manifold makes the motor filthy. when i pulled my manifold it looked like the inside of a bbq pit.