I’m driving a 2003 Chevrolet Express 3500 with a Vortec 6000, LQ4 6.0L V8 MFI LS Gen III, 5964cc, 364ci engine that had a bad idle until the engine reached operating temp. Working to confirm the IAC operation it was trashed.
Your van may have this same fix if your VIN is the same +/- the 9th #. The first 11 VIN are 1GCHG35U231xxxxxx minus the vehicle serial #. I have gotten feed back that one IAC from my preferred group is for the ’N’ engine but did not chase this down.
If you just want an answer that may apply, or not, jump to the bottom.
First off:
When I got the van used, I downloaded the vehicle specs, from where I do not recall, and it is “supposed” to have an electronic throttle body. But it does not. It has a Drive-By-Cable (DBC) throttle body. There are plenty of 6.0L V8 engines with DBC throttle bodies.
But there is no IAC for my van. The throttle body IAC and TPS are an assembly, that is discontinued.
Second:
Some speculation is that because the 2003 van was a transition year and built in 2002 for ’03 sales, it was likely a mix of parts from other production lines. This mixed Drive-By-Wire (DBW) and a DBC throttle bodies. The DBC being the previously mentioned GM throttle body assembly.
Third:
The Vortec 6000, LQ4 6.0L V8 MFI LS Gen III; 5964cc, 364ci w/ cable operated throttle body is not a new animal. You can find lists of LQ4 applications if you look. So I believed there was an IAC out there. Hell - there is one in the van I need to replace!?
Forth:
Working through interchange #s for the P#20663 over J1702L, Made in Mexico, that was on the IAC removed and the GM P#12596575 (assembly), and from a YouTube P#980-005 reference; I worked my way down to 13 IACs, that fall into 2 groups without any overlap. Except for Delphi there are no dimensions or additional information and when you drill down on parts sites, and manufacturers of the IAC is not for a 2003 Chevy Express 3500, even with the specified engine.
Group One is from the removed IAC:
Delphi CV10017
ACDelco 2171806
SMP AC234
UMP IAC47
IPD 457069
AUTEX 958074
Holley 543-34
FiTech IAC #70050-13
Group Two is from the GM P# and YouTube reference:
Delphi CV10011
SMP AC147
UMP IAC33
Autotechnica GN1317577
Beck Arnley 1591032
Curiously, of two IACs I believed fit there was only a 0.01” (-) difference in the step motor operation. With something that small I have to wonder how much off the idle could be during warm up and at a stop
Fifth:
Drilling down on throttle bodies, I found an after market manufacture of two throttle bodies for the ’03. The one that comes up in relation to the first group of IACs, does not match the existing throttle body, and does not include an IAC; and the one that comes up with the second group of IACs matches the installed throttle body, and also does not come with an IAC. At this point I could have just bought any IAC and tried it. But the one primary (name) manufacturer of IACs from both groups indicated neither was for a Chevy Express 3500 of any year w/ a 6.0L V8.
Sixth:
I researched engine rebuilds and found a reference to a Holley throttle body that could take the original IAC and TPS. Also in the same article another ‘performance’ throttle body maker, I contacted, saw no reason the IAC in the throttle body they make would not fit the Holley. I contacted Holley tech support and got a warm ‘they know what they are talking about feeling”. Granted, at this point, I had a large back log of knowledge to bounce off what was being told to me.
A Choice:
It would be the Holley 543-34 IAC or the Delphi CV10017. Both have, like many, if not all, of Group One, the orientation of the connector matching the original. Even though the Delphi had a better warranty it was also more expensive. There are all the other choices in Group One but I wanted to support a supplier that was aware of what they were selling and it was still a guess so I took a middle of the road price.
I ordered and installed a Holley 543-34 IAC. I did the reset sequence, and the start-up idle was normal. Reset is 10 sec to ignition On and 5 sec to ignition Off and then to Start.
Conclusion:
At this point I believe that the 2003 Chevy Express 3500 6.L V8 is “supposed to be” a drive-by-wire throttle body not a drive-by-cable. Never mind the GM P# is the entire throttle body assembly, which is drive-by-cable. So aftermarket suppliers don’t know the difference.
What I do not know is why there was a complete dead dash and Start as a prelude to the bad idle. The IAC is just what was in the way of me knowing if something else was happening. Yes I did parasitic drain testing. As of now everything is working.
After The Fact:
So far so good. I have driven out a half dozen times without issue. I never tracked the start-up idle cycle before and now it seems that the new cycle is revving a bit at the start before quickly settling to the warm up idle. I will be curious to see how this might impact mileage.
Your van may have this same fix if your VIN is the same +/- the 9th #. The first 11 VIN are 1GCHG35U231xxxxxx minus the vehicle serial #. I have gotten feed back that one IAC from my preferred group is for the ’N’ engine but did not chase this down.
If you just want an answer that may apply, or not, jump to the bottom.
First off:
When I got the van used, I downloaded the vehicle specs, from where I do not recall, and it is “supposed” to have an electronic throttle body. But it does not. It has a Drive-By-Cable (DBC) throttle body. There are plenty of 6.0L V8 engines with DBC throttle bodies.
But there is no IAC for my van. The throttle body IAC and TPS are an assembly, that is discontinued.
Second:
Some speculation is that because the 2003 van was a transition year and built in 2002 for ’03 sales, it was likely a mix of parts from other production lines. This mixed Drive-By-Wire (DBW) and a DBC throttle bodies. The DBC being the previously mentioned GM throttle body assembly.
Third:
The Vortec 6000, LQ4 6.0L V8 MFI LS Gen III; 5964cc, 364ci w/ cable operated throttle body is not a new animal. You can find lists of LQ4 applications if you look. So I believed there was an IAC out there. Hell - there is one in the van I need to replace!?
Forth:
Working through interchange #s for the P#20663 over J1702L, Made in Mexico, that was on the IAC removed and the GM P#12596575 (assembly), and from a YouTube P#980-005 reference; I worked my way down to 13 IACs, that fall into 2 groups without any overlap. Except for Delphi there are no dimensions or additional information and when you drill down on parts sites, and manufacturers of the IAC is not for a 2003 Chevy Express 3500, even with the specified engine.
Group One is from the removed IAC:
Delphi CV10017
ACDelco 2171806
SMP AC234
UMP IAC47
IPD 457069
AUTEX 958074
Holley 543-34
FiTech IAC #70050-13
Group Two is from the GM P# and YouTube reference:
Delphi CV10011
SMP AC147
UMP IAC33
Autotechnica GN1317577
Beck Arnley 1591032
Curiously, of two IACs I believed fit there was only a 0.01” (-) difference in the step motor operation. With something that small I have to wonder how much off the idle could be during warm up and at a stop
Fifth:
Drilling down on throttle bodies, I found an after market manufacture of two throttle bodies for the ’03. The one that comes up in relation to the first group of IACs, does not match the existing throttle body, and does not include an IAC; and the one that comes up with the second group of IACs matches the installed throttle body, and also does not come with an IAC. At this point I could have just bought any IAC and tried it. But the one primary (name) manufacturer of IACs from both groups indicated neither was for a Chevy Express 3500 of any year w/ a 6.0L V8.
Sixth:
I researched engine rebuilds and found a reference to a Holley throttle body that could take the original IAC and TPS. Also in the same article another ‘performance’ throttle body maker, I contacted, saw no reason the IAC in the throttle body they make would not fit the Holley. I contacted Holley tech support and got a warm ‘they know what they are talking about feeling”. Granted, at this point, I had a large back log of knowledge to bounce off what was being told to me.
A Choice:
It would be the Holley 543-34 IAC or the Delphi CV10017. Both have, like many, if not all, of Group One, the orientation of the connector matching the original. Even though the Delphi had a better warranty it was also more expensive. There are all the other choices in Group One but I wanted to support a supplier that was aware of what they were selling and it was still a guess so I took a middle of the road price.
I ordered and installed a Holley 543-34 IAC. I did the reset sequence, and the start-up idle was normal. Reset is 10 sec to ignition On and 5 sec to ignition Off and then to Start.
Conclusion:
At this point I believe that the 2003 Chevy Express 3500 6.L V8 is “supposed to be” a drive-by-wire throttle body not a drive-by-cable. Never mind the GM P# is the entire throttle body assembly, which is drive-by-cable. So aftermarket suppliers don’t know the difference.
What I do not know is why there was a complete dead dash and Start as a prelude to the bad idle. The IAC is just what was in the way of me knowing if something else was happening. Yes I did parasitic drain testing. As of now everything is working.
After The Fact:
So far so good. I have driven out a half dozen times without issue. I never tracked the start-up idle cycle before and now it seems that the new cycle is revving a bit at the start before quickly settling to the warm up idle. I will be curious to see how this might impact mileage.
