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
109,885 POSTS

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

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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

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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.

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

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

It should set the check engine light.

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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.