1998 2.4L 2WD with P0401 code

hi all.

I'm trying to track down the issue with the truck.
This is what I have checked so far.

1. Removed and cleaned Temp Sensor by EGR

2. Removed vacuum line to EGR and applied vacuum valve moves and engine stalls. also EGR holds vacuum.

3. Bypassed vacuum regulator and connected P and Q lines, reved engine and I block the line out of the VSV, EGR opens.

4 I want to test the EGR vacuum regulator but don't have the correct procedure for the 98 2RZ-FE

can anyone help with the FSM for this engine...

Thanks in advance.

 

Remove the EGR vacuum modulator. Apply a small amount of vacuum (10-15 in Hg) to the bottom hose of the modulator. If it doesn't hold vacuum, the rubber diaphragm inside has a hole. It gets old and brittle and eventually gets a split causing a small leak, then the EGR valve doesn't open correctly or enough.

 

YUp, modulator diaphragm is busted, I also confirmed by opening it up. Cracked!

I also tested the switch with a 9v battery and it clicks and opens the valve.

I'm curious on how this system works.

My guess is that the switch opens under load to close the EGR and allow more power to the engine. Under light load the switch remains closed and the pressure under the modulator from the EGR and some vacuum from port R allows vacuum from P to open EGR.

There are 3 vacuum ports on the throttle body that connect to the modulator Q R and P. they are at different locations on the throttle body, I don't have a vacuum gauge but i believe they pull different amounts of vacuum Q being weakest to P strongest.

Well, now that I need a modulator, PN 25870-75040, where can i get one for the least amount of money, I see some under $20 but with a different PN 25870-75090...can that work?

Any source for aftermarket parts? I don't trust Ebay sellers that claim some part numbers will fit.

Thanks in advance.

 

Hey thanks for updating us. Personally have the same 98 2.4L Tacoma, but is the SR5 model and I needed a 25870-75030 modulator instead of the one you had. I wouldn't go switching up the part numbers of other cars though since they are made specifically for a reason.

EGR parts specifically often come in branching parts one for automatic, and the other for manual, so I'd assume they are inherently different in how they operate. Thats not including how a EGR component works with a total different engine on a different car/truck.

Certain things like internal engine parts I'm just personally weary of using anything aftermarket. If it was a gas pedal cover, door handle, or wiper blades, aftermarket would be fine by me but for something as important pertaining to the EGR system I go OEM for the piece of mind alone haha and its not that much more expensive. Then again both our OEM parts failed so its a tossup haha.

Personally just got a OEM modulator for 50 bucks from Amazon, and thats only 20-30 bucks more then a aftermarket one. Haha that all said if you want to risk trying a cheaper option I'd love to hear how it goes.

 

My tacoma is manual, maybe that's the reason for the different PN. like you said maybe the spring and ports are different specs. I noticed that for the aftermarket no name part the sellers on ebay lists all sorts of cars. claiming part will work on them, a lot of listings on ebay claiming that the 25870-75090 works on my truck, I bit the bullet and found the OEM on ebay for $50 shipped.

 

Ah it seems the PN differences definitely line up since I have a automatic. Hope your new part works out well.

Always have to be wary of figuring out which parts fit when it comes to aftermarket, and luckily most of the things I found seemed to work. But, it always seems like I have to do detective work as I found many items on both Amazon/ebay saying they would fit when they don't. Usually I try the best I can to compare the items visually, and read the reviews to see if someone with the same model vehicle I have ran into a problem or if it worked out (Forums/Youtube as well). Often times that saves my behind haha.

 

The VSV allows air through in certain conditions. Engine warm and not idling and maybe not under full throttle.

The modulator balances the amount of exhaust gases going in based on vacuum before and after the throttle. I've stared at the diagrams in the repair manual and it's still hard to figure out exactly how it works. I just know it's a delicate balance and tuned specifically to the engine.

The modulator should last another 15-20 years, so I figure the cost is small in the long run and it's worth going with a Toyota part.

 

Several weeks of driving with new modulator and the code has not returned. So All is good! Thanks

 

Aw yea good to hear! Same thing for me as well - new modulator and no more code since. Thanks for reporting back, its always great hearing good news and problems solved.