1999 Chevy Silverado engine misses once warm and under load

JJROBJOHN

MEMBER
1999 CHEVROLET SILVERADO
6 CYL
2WD
AUTOMATIC
186,000 MILES

I have a 4.3 l and all of a sudden it has a miss when it is warm. It idles excellent but once it warms up it misses like crazy. I changed the plugs, cleaned EGR valve, wires are good but still has a miss when warm. When cold in the morning it runs excellent with lots of power.
Please help with any solutions

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,205 POSTS

Did you check for vacuum leaks? Also, has the check engine light come on? Also, have you checked fuel pump pressure?

Was this

answer

helpful?

Yes

No

Tuesday, May 5th, 2009 AT 7:51 PM

JJROBJOHN

MEMBER
3 POSTS

I have no vacuum leaks and I did have my check engine light on. The code was 4020 which was left side catalyst problem

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

Saturday, May 9th, 2009 AT 6:54 PM

JJROBJOHN

MEMBER
3 POSTS

I am wondering if I have a problem with my pre converter oxygen sensor. I tried unplugging it but I don't know if that would do anything.

Was this

answer

helpful?

Yes

No

Saturday, May 9th, 2009 AT 6:57 PM

JACOBANDNICKOLAS

MECHANIC
108,205 POSTS

It should set the check engine light.

Was this

answer

helpful?

Yes

No

Saturday, May 9th, 2009 AT 8:03 PM

JJROBJOHN

MEMBER
3 POSTS

I unplugged the oxygen sensor and drove around for about 15 minutes. I did not get the check engine light on and once the truck warmed up just under half on the temperature gauge the rpm tach started to go from 2000 to 5-6000 constantly. (Fluttering)When this happens if you give it hard throttle it starts to hesitate and miss. But when it is cold in the morning the truck works excellent.