Having a p0402 for a few years that was getting progressively worse, I decided to dive and and do a few things. Checked EGR and modulator, modulator was not consistent so replaced that. Cleaned out in between the two hoses from EGR to intake, intake to VSV and that is carbon free, plenty of other posts on that fix. All other hoses got replaced as they were cracked and orginal. But the P0402 persisted and I found the culprit in the TB. But first, a few things to check.
When the VSV gets 12V, the valve inside turns and no air can pass it. So I used this link to check the VSV operation, worked perfectly and no need to remove the throttle body to check. I used a vacuum pump to test for flow. Disconnect the hose from EGR to VSV (intake) and test with no power on the VSV. There should be no vacuum. I had some vacuum!
forum.ih8mud.com
Connect the the VSV to 12V on the battery with and the vacuum is perfect as it should, VSV is actuated. A couple of alligator clips do the trick, vacuum pump again to check flow. Disconnected from battery and vacuum would hold on, but slowly go to zero.
On the diagram above the vacuum line shows going from VSV to a T intersection, then to the TB. This TB line is easy to get at with needle nose pliers on the TB under/forward section. Disconnect this line and do the vacuum test again. This time, there was zero vacuum with no power to VSV, and perfect vacuum with power applied. So the problem is not the VSV or lines, its in the TB itself.
First, used carb TB cleaner with long hose to spray in there, see if we can break up the buildup.
Afterwards test the vacuum again to see if blockage is removed. If not, then the TB needs to come off, but leave the throttle and cruise cable connected, plenty of room to maneuver when you disconnect all hoses and electrical plugs.
Follow the opening from the intake to the TB where the hose connects, and on the other side there should be a hole. The hole is where this yellowish piece of crud is. Clean that off with a small wire and more carb cleaner.
This is the same hole, now cleaned up.
Now put it all back together and go for a test drive. I will need to go through a few driving cycles to ensure the P0402 is gone, but in my case it would come on immediately at startup, and so far it is clear.
When the VSV gets 12V, the valve inside turns and no air can pass it. So I used this link to check the VSV operation, worked perfectly and no need to remove the throttle body to check. I used a vacuum pump to test for flow. Disconnect the hose from EGR to VSV (intake) and test with no power on the VSV. There should be no vacuum. I had some vacuum!
Checking VSV for EGR easy way P0401
Well I got bit with that bug too. Sorry if I missed something, although most common culprit has been long identified - VSV, most of ways to check its operation are rather tedious. Here is my easy way. Disconnect VSV connector from main engine harness. Check for continuity between two terminals...
forum.ih8mud.com
Connect the the VSV to 12V on the battery with and the vacuum is perfect as it should, VSV is actuated. A couple of alligator clips do the trick, vacuum pump again to check flow. Disconnected from battery and vacuum would hold on, but slowly go to zero.
On the diagram above the vacuum line shows going from VSV to a T intersection, then to the TB. This TB line is easy to get at with needle nose pliers on the TB under/forward section. Disconnect this line and do the vacuum test again. This time, there was zero vacuum with no power to VSV, and perfect vacuum with power applied. So the problem is not the VSV or lines, its in the TB itself.
First, used carb TB cleaner with long hose to spray in there, see if we can break up the buildup.
Afterwards test the vacuum again to see if blockage is removed. If not, then the TB needs to come off, but leave the throttle and cruise cable connected, plenty of room to maneuver when you disconnect all hoses and electrical plugs.
Follow the opening from the intake to the TB where the hose connects, and on the other side there should be a hole. The hole is where this yellowish piece of crud is. Clean that off with a small wire and more carb cleaner.
This is the same hole, now cleaned up.
Now put it all back together and go for a test drive. I will need to go through a few driving cycles to ensure the P0402 is gone, but in my case it would come on immediately at startup, and so far it is clear.
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