P0401 code questions

[BLRobertson]

Our 2000 Camry 2.2 L 105 K check engine light came on and after I got the code read it's the P0401 low EGR flow. They immediately want to sell me a $200 EGR valve which I declined and came here to check posts and the PDF service manual(great reference material THANKS). First I checked all vacuum lines for condition and blockages-all good so far. I pulled the EGR valve which showed little or no carbon build-up but cleaned what I could. Removed Throttle body and clean all ports and passages. Opened the modulator and cleaned filter screen. Went to our Toyota dealer for gaskets and one of the mechanics asked if the filter screen had a dark spot on it which would indicate a pin hole in the diaphragm. I had seen this so I picked up a modulator also. I re-installed all my parts, cleared the code and it stayed off for a couple days and back on again. That was a year ago and my wife has been working 125 miles away from home so no time to really get into this. Now she's back and it's time to fix it. I followed the checks in the maintainance manual and everything's operating properly. Re-checked everything cleaned EGR valve and Throttle body again. I've checked vacuum readings while driving and Port R has little or no vacuum under any throttle positon Port Q flucuates from 0-15 and bounces around at a steady RPM over 2000 rpm. Port P shows 0 to a max 2.5 and EGR port also shows 0-2.5. The EGR requres 3-3.5 inches to fully open so it seems I not getting enough vacuum to the modulator or to much drop through it. We're getting too deep into the theory of operation here and I need some help. Sorry about the long post but I feel like I've looked into everything on this EGR system 4 times and still can't fix it.Any ideas will be appreciated. Thanks

[Brian R.]

Have you downloaded the factory service manual from here? (from the sticky post at the top of this forum). The diagnostics and other referenced volumes gives a step-by-step procedure for this and other trouble codes. I could read it and provide you directions from this manual, but it would be a waste of time to recite what is in the manual since you can (or have) read it yourself. If you have, perhaps you missed a step.

Once you check out this proceedure and have gone through all the steps, come back and we can see if there is something else we can come up with.

[BLRobertson]

Brian R thank you for your response. Yes I've printed out the service manual relating to the EGR and VSV components and followed each step. Nothing out of specs showed up. I guess my more direct question would be what vacuum readings should I be seeing at Port R and Port Q when the system is operating properly. I'm thinking the readings should be much higher than what I'm seeing. I'm going to pull the throttle body and clean it again maybe I missed something. Then go through the troubleshooting checks again. It's been a while and I don't remember if I pulled the IAC apart. When cold it doesn't seem to idle any faster like I think it should during a warm up period. What do you think, could this have anything to do with my low vacuum readings?

[BLRobertson]

Sorry I need to straighten out which ports I'm wondering about. Port R form the throttle body to the modulator(fwd hose) and Port P from the modulator to the VSV. Thanks

[Brian R.]

Doesn't port P simply actuate the VSV? If so, then whatever vacuum is adequate to switch the valve on and off is sufficient. The check of the throttle body indicates that any positive vacuum is expected off-idle.

I don't expect that the EGR valve needs to be fully opened to allow flow. 2.5 in may be enough for its purpose.

Port R doesn't seem to be expected to provide vacuum at any throttle setting.

Have you tested the MAP sensor?

Have you tested the throttle opener setting? See page SF-30.

[BLRobertson]

Got a chance to check the map sensor. I back probed the connector and my voltage drop fell within specs. Throttle opening setting showed 1300 RPM. What purpose does the smaller hose coming up from a 6x6 black plastic box up to the intake hose serve. I found a tear in the folded portion that I hadn't noticed before. I've done a temporary repair to it but didn't change the CEL from returning.I agree that 2.5 inches will open the EGR valve about half way and allow flow through it. What is the PCM looking for to determine the EGR system is operating properly. With no positon sensor on the EGR valve I'm guessing it's monitoring something else.

[Brian R.]

Here's a post in the FAQ thread with some really informative documents.

Particularly read the one on EGR.