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Old 12-20-2008, 09:56 PM
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Default Vacuum spec at Port R on Throttle Body?

Long time, no visit. I have an upcoming smog check (22RE engine), and since I just barely passed my NOx test two years ago, I'm nervous about passing it this year. Based on those tests, and my somewhat lackluster engine performance lately, I think I may have some EGR operational issues. I went through the checks in the FSM, and that all checks out fine. However, I decided to check the vacuum for the "R Port" and "E Port" on the throttle body (since those control the EGR function), and got some strange results. The FSM says I should be able feel vacuum on these ports at 3000 rpm, and no vacuum at idle. I decided to get more scientific about it, and hooked up my vacuum gauge to the ports instead. On the E Port, I get strong vacuum around 3000 rpm. Like around 15 mm Hg as I recall. On the R port, I get barely anything (4 mm Hg or even 0). Thinking the R port was plugged with carbon, I sprayed throttle body cleaner down the port, and also blasted it with compressed air. On top of that, I poked a thin wire all the way through it, and moved it back and forth. Seemed like it was clean to me, but when I checked it with the vacuum gauge, it didn't seem any better. I can't figure out why it so low, when the E (and also P) port seem so strong. Anyone have any suggestions? Could it still be plugged up after all that, or is it supposed to be that low. One thing I did notice is that the vacuum at the R port jumps during the process of twisting the throttle, but won't stay steadily high like the other two. Also kind weird.
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Old 12-21-2008, 11:57 AM
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It's refered to as ported vacuum. It only activates during acceleration. It's used for certain functions like distributor vacuum advance or egr activation.
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Old 12-21-2008, 04:56 PM
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OK, that makes sense, as I only seem to get a vacuum reading on it during the throttle twisting itself, not during a steady state throttle. I guess the manuals are wrong then, as they imply you should feel a vacuum at a steady 3000 rpm?
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Old 12-21-2008, 07:13 PM
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The manuels aren't wrong , they just say you should feel a vacuum . They just don't say how much you should feel. The reason you don't feel it as strong at a steady throttle opening is that most vacuum ports are on the engine side of the throttle plate where vacuum is strongest at idle or at low steady throttle openings. Portrd vacuum is on the atmospheric side fo the throttle plate, usually just on this side of the throttle plate. As the throttle is opened a low pressure condition is created at the area of the throttle body where this port is located and you get a stronger reading, but once the engine is at a higher rpm range the vacuum drops on the ported side and rises on the manifold side.
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Old 12-26-2008, 08:06 PM
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Funny thing... I have an old Haynes manual (about 15 - 20 years old) that is my primary manual that I keep in my garage, and I have a newer edition (about 2 years old) that I keep in my 4Runner for on the road repairs. My old manual says I should sense vacuum at the R port, while the new Haynes manual says I should not sense any vacuum at the R port! I'm guessing the old one is wrong, as I can't sense any during steady 3000 rpms.

On a brighter note, today I took my EGR valve off the vehicle to inspect and clean it (if necessary) and discovered that the little exhaust port that feeds the EGR valve modulator was completely clogged up! Couldn't blow 2 molecules of air through it. So after much effort, I was finally able to remove all the carbon build up inside, via solvent cleaning, poking at it with wires, etc. Finally, I cleared it out. Took it for a test run. Seems like there is some marginal improvement in the operation of the vehicle, but still is rough at times. My emissions testing should go well after this, I hope.
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