A few questions

[eastman51]

Hello, I am new to the forums. I bought my 95 SC 2wd back in February of this year, and its had a ton of problems. Started and drove reliably, but whew, so much wrong. I've finally caught up on a lot of things, but there's some stuff left to do and would like some advice on how to proceed.

I'm looking to change the transmission fluid soon, and originally wanted to do a flush. But at 226k miles, I'm wondering if that's a bad idea. But I think I should at least change the filters.
I'm also going to change the supercharger oil, probably just with AC Delco if that's fine.

I know my SADS couplings are torn and there is some play in the shaft, but zero noise and the accessories seem to run just fine. I'm seeing on the forums that some kind of BMW coupler is good, but you need to modify them to fit; however I seemed to only see that on posts for earlier year vans. If the later years have larger bolts, does that mean you don't need to modify the BMW couplers?
I'm also going to change all the V belts and tensioners when I do the SADS couplers eventually.

I am fairly certain my oil return pipe leaks. The whole bottom of the engine is covered in oil. I have already changed the valve cover gasket, and that does not seem to be leaking anymore.
And the transmission mounts are tearing.

The things of my more immediate concern:

The coolant in the reservoir looks a little dark, and I have no idea when it was last changed. The van reaches and maintains temperature just fine, but I do want to change the coolant for good measure. I also want to replace as many coolant hoses as possible; or at the very least, the primary radiator hoses and any other hoses that are prone to failure. I'd rather not let my headgasket die because I didn't replace a $2 hose. I would also replace the thermostat.
Looking in my FSM, the water pump looks to be really easy to swap out. Should I replace it while I'm already servicing the cooling system? I believe my oil filter pedestal also leaks, so maybe I should just since I could already be there?

The EGR. I tested the EGR components under the seat, and they hold vacuum. My code is just the flow insufficient. I already took the air inlet off and cleaned that side pretty good; but I remember not being able to remove the EGR. That stupid flare nut on the pipe going back to the cylinder head is seized on there good. I could spin it with a lot of force, but it didn't really move easily; I also broke my 3/8" u-joint trying to loosen it.
My CEL has not gone away, so I need to take another stab at cleaning the passage. My idea was to unbolt the EGR from the intake and remove the EGT, then fit a carb cleaner can's hose between the EGR and the intake, then spray and pray.
The other issue I have with the EGR is that after my last attempt, it started to make a high pitched noise. I think it comes from that giant flare nut, since I don't think I moved the pipe around with enough force to bend/crack it. My thought was to use muffler repair paste or exhaust RTV around the flare nut to hopefully stop that. If I ever had to replace the EGR, I'd have to cut it off regardless.

My ac does not work because of a leak at the union up front between the drier and the ac compressor I believe. The pipe on the drier side of the union has a gash that goes behind the flare nut, so it leaks all refrigerant within a couple days. I have no local junkyards with a Previa, and you cannot get this pipe from Toyota. Not entirely sure how to proceed on this.

I will be taking the van back to the dealership sometime next week. I had them rebuild the differential due to a bad bearing a few months ago, and its still howling. At the time, my flex pipe was completely busted and the exhaust was just a mess entirely; but now I have put a new exhaust on and the diff howl is unbearable on the highway, and very annoying while slowing down in any situation.

Edit: I am also probably going to make a custom harness for the headlights. Mine are effectively useless, despite doing a Chrisfix headlight restore and brand new bulbs. Good to know its a common issue though!
I believe I saw a wiring diagram on the site that is supposed to sell harnesses, but I will have to look it over again.

[Previologist]

its worth saying again over here, if only so someone will try and prove me wrong.

Old filthy transmission oil is bad for transmissions. Fresh clean oil is good for them. If a tranny fails after a flush it was gonna fail anyway.

[89van]

Hmm, I would love to try this on my '89 TV (Yes I know i have no business here on the Previa sections for the time being) but if it does fail my TV will be out of action to find a replacement be it automatic or manual, although I have my doubts as the transmission works fine as of now for will it survive a flush; L,2,D, Reverse is a bit shaky though but the last time it was changed before I owned it is unknown . I will replace the ATF on my '02 Saturn L200 and my '06 Kia Sorento now that they're both reaching the service intervals for the ATF per the owner's manual and report back how it goes.

[pdgizwiz]

Congrats on your purchase! While Previas are becoming increasingly rare, they are still amazing, unique, and worth maintaining, IMHO.

Transmission - I suppose the best thing would be some kind of flush process that purged all the old oil and replaced it with new. But being a staunch do-it-yourselfer I don't have the gear for such an operation, and imagine that doing this would take a lot of flluid. What I've done with apparent success is just to drain out what I can and replace it. You wind up with about 3/4 new oil that way, which is a dramatic improvement over 100% old fluid. I think if one was to do this every 50k miles or so, your transmission would be very content for a long time. As I have too many vehicles to drive any of them very much, that's a long time for me. One other tip: try to measure what you get out and put as much back in. This reduces guesswork reading the dipstick.

SADS couplings - I've no experience with the BMW couplers, so am not in a position to say this is a bad idea, or doesn't work. But I tend to respect designers' intent, and am more comfortable with stock designs. The SADS system is admittedly a weak link in the Previas, but we're talking about vehicles that are 24+ years old here, and rubber parts just don't last that long. I've devised a way to rebuild the couplers, as you might see in some of my earlier posts. They work like new.

Coolant - By all means drain and replace the coolant. Use the correct Asian stuff. It is pink, I believe. Not green.

Water pump and oil filter pedestal - I agree, do them both. The pumps are fairly cheap. There's a special gasket under the oil filter pedestal that looks like a figure "8". It will be old and brittle, so replace it.

EGR pipe - this is a lot easier to get ahold of and loosten if you take the starter off first, especially since your van is 2WD.

Coolant hoses - while you're under the engine, replace the small water hoses that connect to the various tubes on the intake manifold. I think there are three of them. There is another critical water hose at the upper right of the engine that connects to a steel pipe under the floor. I've think I've seen this referred to as the "hose of death". It can be a bit of a bear to get ahold of. But you could sleep easier if it's been renewed.

Differential - It sounds like you dealer SWAG'ed this and it made no difference to anything but your pocketbook. I'd try to find a junkyard replacement for the entire rear axle if you confirm that it the source of your noise. You'll need to find one from another S/C van either with or without ABS to match yours. Have you tried greasing the slip joint in your driveshaft? Checked the U-joints?

Headlights - I recently renewed a pair of badly yellowed '91 Previa headlights using a 3M kit that involves three stages of wet sanding with disk/drill, and wipe with a sealer/UV inhibitor. I spent a lot more time with this than the box advertised, but the result is headlights that look like new. I took the headlights out so that I could do it all on a bench indoors, which helped make the process a lot more pleasant that it would have been had I been crouching and contorting myself at knee level.

[eastman51]

Transmission - Yes I think I'll probably just do a drain and fill, replace the filters and the pan gasket.

SADS is fairly low on my priority list right now considering it seems to be ok despite the play.

Yeah I know it has green coolant in it now, which is fine, but not correct. My 95 Corolla was the same way, had ugly looking green coolant that I flushed out for fresh red juice.
Hose of death type stuff was exactly what I was looking for! The 90s Corollas have a little hose on the back of the water pump people tend to neglect, so I was wondering if these vans had something similar.

At this point I don't think I can be asked to deal with the EGR pipe. If I have to I can try removing the starter, but from what I recall I don't know if that would actually help.

The dealership did *something* to the diff. It used to make horrific grinding noises and howled on the highway, now it just howls on the highway and whines on deceleration. I believe that they actually took the diff apart, but I suspect they either didn't shim it correctly and/or didn't touch the ring and pinion at all. I'll take it to them and see what they'll do; I took it in to avoid having to try sourcing a used axle in the first place. There's absolutely nothing for junked or part-out Previas in my state.
I had the u-joints replaced earlier this year because they squeaked.

I did a similar treatment to my headlight housings. I don't think mine turned out as well, but it's still a big improvement. I'm going to try making a new headlight harness that piggybacks off the stock harness, there's a link to the website with diagrams and explanations in the "led headlight conversions" thread from earlier this year.
I added some fog lights to help, but they obviously only help so much being so short range. Not to mention I need to remount them since they're crooked right now, lol

[Jonny]

Re egr problems ... it must be verified that the vacuum modulator/solenoid is functioning as the very first step in the process. It is this part which tells the egr valve to open. Search vacuum modulator for more info. Clogged passageway at intake port is usually by-product of egr valve never opening.

[eastman51]

That was the very first thing I checked. I pulled vacuum on the EGR and the modulator to ensure they are functional.
The EGR system on late 80s and most 90s Toyotas all work basically the same from what I've seen. I had to replace the modulator on my 95 Corolla a while back, so first thing I did when tackling the EGR code was make sure I didn't need any parts. The Corolla not only had a clogged intake but had a busted modulator, it's EGR valve was fine.
My van only has an insufficient flow code, and not an "EGR failure" code.

[Jonny]

My suspicion is still with something in the modulator circuit. Insufficient flow could also mean no flow, I would expect. The EGR valve is most likely not opening, but as you said, the EGR valve could still be functional. Any one of the entire modulator vacuum system's multitude of components could cause the problem, and on my '91 there were multiple compounding problems.

Do you have a repair manual for your year? (edit - from an earlier post I see you do)
Where did you apply vacuum to the modulator, and was the modulator still installed when you did it?

[eastman51]

I pulled vacuum on the small nipple on the EGR itself, and pulled vacuum on the bottom of the modulator. Just like I did with my Corolla to determine it needed a new modulator. Both were a-ok last I checked on the van. I left the modulator alone, just unhooked it from the big port on the EGR and pulled vacuum.

The Corolla's OBD1 spit EGR failure, but the van's OBD2 is just telling me flow insufficient; I haven't really thought to check the FSM for code set criteria tbh. Everywhere I searched online for that code for Previas indicated that cleaning the passage alone fixed the problem.

[Jonny]

My California spec '91 has an OBD1 and a different (single) code for EGR problems, but the code was from a sensor in the passageway sending a temperature signal to the ECM. On mine if the passageway doesn't have enough hot gas flowing through it the code is "EGR gas temp too low". The OBD2 system on your '96 sounds slightly more sophisticated. Too bad it is still obtuse about the source of the problem. The "insufficient flow" sounds very similar to the "EGR gas temp too low". in what is actually being sensed

Anyway, my '91 service manual has a whole bunch of vacuum tests to verify the entire EGR system on the vehicle both warm and cold, and I do remember that when I was diagnosing my problem that when I did the tests something was clearly wrong (I forget the details) and it led me to the modulator. I'm sure your manual has some similar tests outlined within. My modulator had a torn diaphragm (if your test on the bottom port of the modulator held vacuum, your diaphragm is fine), the pipe tree had rusted completely closed on one or both of the P and R pipes, and the passageway port at the throttle body was clogged with carbon. All three of these problems had to be found and solved before the CEL went away.

Maybe do all the tests in your FSM, exactly as written, to see if that leads you anywhere. The two vacuum tests which I understand you have done would not have found a clogged tree pipe or a bad BVSV, for example. If the vacuum test directly on your EGR valve does indeed cause engine stumbling at idle it would suggest the EGR gas passage is open and no work is necessary on that EGR valve - exhaust connector pipe.

Edit: I made the assumption, erroneously perhaps, that the vacuum test you did on the EGR valve itself was done with the engine at idle and that it stumbled or died on you, indicating good EGR valve and open EGR passageway. If this is not the case, do this test. No change to the engine rpm means EGR valve is bad or you still have a blockage somewhere between the exhaust and the throttle body port.

[eastman51]

Yea I'd have to look in the FSM for 95 to see what the EGR codes are, and their criteria. My van is quite weird, it has an OBD1 port under the seat but also an OBD2 port under the fuse panel cover. I haven't actually hooked up my OBD1 plug to the OBD1 to see if it works since OBD2 is clearly superior.
I should see if my reader can see EGTs off the sensor in the passage, that could potentially lead me somewhere if there's data to steer me in the right direction there. Other than that, I can do the rest of the test suite. I only performed the exact same tests as I did on that Corolla, but not the full FSM procedure. The EGR valve was tested engine off, but this was before I cleaned the inlet port so it wouldn't have made a difference at the time anyway.

Edit: I haven't thought anything of it, but I do specifically remember something after I cleaned the inlet port. I cleaned it all up, put it back together and drove around. My CEL came back on, which I checked and the only code was "Insufficient temperature for closed loop operation." I used live data to verify that an O2 sensor was dead with 0v. I was not surprised since one of the codes back when I bought the car was "downstream O2 sensor." Since then I replaced the whole exhaust system with new O2 sensors, and when the CEL came back it was once again the "flow insufficient," which it has had since I bought the van excluding the singular time I checked and it wasn't there. For all I know the modulator has failed after the cleaning, or some other issue is now being exposed as the EGR attempts to operate with the engine now running in closed loop.
At a minimum I need to retest the modulator and try the idle test on the EGR to verify the passage flows.

[eastman51]

I finally got around to checking the EGR valve and now have an update.

I scanned in the pages from the FSM for this DTC, so I am now armed with what Toyota considers to be the causes. However, I also pulled vacuum on the small EGR port at idle to see how that would affect things. Nothing was changed. So, either the EGR valve has failed (unlikely imo), or the passageway is still clogged. I still need to properly test the modulator, but its not worth my time until I know the EGR flows. If the code remains after ensuring the passageway is clear, I'll delve into troubleshooting individual components as we'll obviously have a part failure.
I will also check OBD2 live data for an EGT PID, see if it says anything. I still hear that whistle noise, so something is happening and it has to be EGR related....

I wish I'd made more progress on the van in the last few weeks, but I picked up another project car smh.

[eastman51]

New update:

The Van has been doing well. As weather warms up, I've been driving my project cars a bit more.

Today I fixed the EGR for good. As I suspected, the passageway was still clogged. Was completely blocked between the EGT sensor and the inlet, just had to remove the EGT and get a better tool for poking the passage from the inlet side. No more CEL!
Additionally, I figured out the source of the strange whistling noise; the EGR itself had no gasket material remaining! Go figure! New gasket and its quiet, minus the rattles of a few heat shields and whatnot. I think I need to unbolt the exhaust from the manifold and realign it because I can tell there's still a small leak. But otherwise the engine is running beautifully. Ideally the EGR being functional should bring me from 17mpg avg to at least 21mpg avg (combining city and highway, I always have a really good mix of both).

Coming up on an oil change soon. I might try cleaning the bottom of the engine to get a better idea of oil leaks, or if it's still all residual. The dipstick level never seems to go down, but I always leave drips behind. *shrug*
Also need to change the SC oil..... I keep forgetting and have had a couple bottles of AC Delco SC oil for a while now lol.

I never did get around to calling up the dealership or otherwise acting on the differential issue. Which is unfortunate since I will be gone for the entire summer starting in just a few weeks, so even if I drop it off tomorrow there's always the slim chance I don't get the van back to prep it for storage.
I changed the diff oil today just to check up on things, and its not looking good to me. The drain plug was stacked with shavings and the oil drained a little grey, also didn't seem to drain a lot of fluid but I may just be paranoid; to support my theory of it being low however, I found seemingly fresh and definitely gear oil on the underside of the rear end just behind the driveshaft. Perhaps the pinion seal was damaged by the dealership, or a new one was installed poorly; either is plausible. I definitely think the whining on decel has something to do with the metal shavings, but if it IS leaking then that could also be the problem. Regardless, this is the dealership's problem (assuming they'll work with me on this, considering they worked on it almost a year ago and something like 2k miles perhaps). I filled the diff back up with a cocktail of Lucas heavy duty oil stabilizer, Lucas 75W90, and some Castrol 80W90 limited slip (was the first thing I saw at the parts store lol). I can tell its much quieter when the diff is cold, but it whines just the same once heated up. I'm going to try my best to get the dealership to fix their mistakes before I leave, otherwise I'll probably just cut my losses and source a used rear end to restore myself this winter. I do need the van this weekend, so hopefully I could get it in next week.

Everything else is non-critical (except for tires, but I don't want brand new tires to rot and flat spot while I'm gone), so its on hold until at least the fall.

[Previologist]

You can stick your finger or a screwdriver or something in the diff fill hole to check the level, so you don't have to guess. Too late now though.