4.8 surge at idle
05-27-2014, 12:28 AM
#1
4.8 surge at idle We have a 2000 Silverado 1500 with the 4.8. It has a surge at anything under 1200 rpm. If you snap the throttle it will hang at 18-1900 rpm and drop to 600, run like crap and stumble its way back up to 714 to 1010 in park. The surge isn't rhythmic. I had 2 codes, one I forced P0102 mass air signal low and the other was P0507 idle control system (RPM too high). I had a bad intake gasket that I replaced, cleaned the throttle body, cleaned the MAF and it still surges. I unplugged the MAF (I believe forcing the code) to put in speed density and it would idle about 1000-1100 rpm and relatively steady so that I could check for vacuum leaks. I borrowed a good MAF from my bosses 2000 5.3 Suburban and no change. I'm thinking that there is a problem with the IAC but I'm not sure. Below are the results from my scanner and they are are the 714-1010 rpm "idle" unless noted. Can you help me out?
TPS 0.59
O2 B1 S1 39
O2 B2 S1 30
02 B1 S2 26
O2 B2 S2 43
INJ PW 3.2 (Both banks)
ST TRIM -1 52
LT TRIM -1 25
ST TRIM -2 52
LT TRIM-2 25
TRIM AVG 0.0 (on all)
FT LEARN YES
FT CELL 17
MAF HZ 2067
MAF GM/SEC 3.14
MAP HG 11.3
MAP V 1.46
BARO HG 28.7
BARO V 4.59
COOLANT 203
IAC POS 0
DES IAC 0.00 (But I did see it flash as high as 1.19 still at idle)
VTD FUEL OFF- What is this?
IGN FUEL VTD NO - What is this?
SPARK ADV 14-16
KNOCK 0
EGR CLSD V .70
DES EGR 0
IGN V 13.8
DES IDLE 575
In the functional tests section I found 3 interesting tests.
IAC function, I could force idle up to 1200 but unless I snap the throttle I couldn't force the idle down below that 714-1010 rpm.
CYL miss index, according to the scanner anything below 1000 is good. At 714-1010 rpm it is 94. After snapping the throttle and getting it to idle down before it climbs back up it was 65526!
CYL MISS FIRE, nothing showing a particular cyl issue. but zero miss fires at that 714-1010 rpm but consistent miss fires between 18-20 per 200 revolutions at that snapped throttle 600 rpm idle.
Sorry for the long post but I just simply don't remember enough on scanner readings.
TPS 0.59
O2 B1 S1 39
O2 B2 S1 30
02 B1 S2 26
O2 B2 S2 43
INJ PW 3.2 (Both banks)
ST TRIM -1 52
LT TRIM -1 25
ST TRIM -2 52
LT TRIM-2 25
TRIM AVG 0.0 (on all)
FT LEARN YES
FT CELL 17
MAF HZ 2067
MAF GM/SEC 3.14
MAP HG 11.3
MAP V 1.46
BARO HG 28.7
BARO V 4.59
COOLANT 203
IAC POS 0
DES IAC 0.00 (But I did see it flash as high as 1.19 still at idle)
VTD FUEL OFF- What is this?
IGN FUEL VTD NO - What is this?
SPARK ADV 14-16
KNOCK 0
EGR CLSD V .70
DES EGR 0
IGN V 13.8
DES IDLE 575
In the functional tests section I found 3 interesting tests.
IAC function, I could force idle up to 1200 but unless I snap the throttle I couldn't force the idle down below that 714-1010 rpm.
CYL miss index, according to the scanner anything below 1000 is good. At 714-1010 rpm it is 94. After snapping the throttle and getting it to idle down before it climbs back up it was 65526!
CYL MISS FIRE, nothing showing a particular cyl issue. but zero miss fires at that 714-1010 rpm but consistent miss fires between 18-20 per 200 revolutions at that snapped throttle 600 rpm idle.
Sorry for the long post but I just simply don't remember enough on scanner readings.
