Lots of Codes -- What to do next?

[cgregs32]

Van: 95 Previa LE altrac s/c

I took my trusty prev into the shop today because of surging acceleration. I thought It was pretty simple fix, I could hear exhaust leaking from the manifold, I thought I would need a new gasket.
Turns out I have many more issues. The shop pulled 17 codes from the van :dizzy:.

(12) No RPM signal to ECW while cranking
(13) RPM signal circuit open or short
(14) No ignition reference signal
(21) 02 sensor circuit problem
(22) Coolant temperature sensor open or short
(24) Air temperature sensor circuit open or short
(25) Lean exhaust
(26) Rich exhaust
(27) Sub oxygen sensor circuit open or short
(31) Air flow meter circuit open or short
(32) Air flow meter circuit open or short
(41) Throttle position sensor circuit open
(42) Vehicle speed sensor or circuit
(43) Starter start signal circuit open or short
(51) TPS idle switch contacts open
(52) Knock sensor circuit open or short
(53) Knock control circuit computer problem
(71) EGR system problem
(99) Continuous flush

What the...?!

Has anyone seen anything like this before? I am trying to figure out where to begin with these issues. What confuses me the most is that my van seems to be running totally fine, other than the surging acceleration.

I do have a second battery setup. It a deep cycle battery connected through a solenoid(grounded) to the to the main/starter battery(also grounded). Is it possible this could be the culprit of all the open or short codes?

Do these codes indicate that my computer is fried? If so, why would my van seem to be running fine?

Sorry for the Blab of information, but I am at a loss here. The shop suggest I do not drive my van because of the (99) code. This will not be an option for very long.
Thanks for reading. Please comment if you have any Ideas. And I will update as I research further.

[cb97alltrac]

Some previas had a knock sensor issue. You can't just change it out its hard to get to without engine removal. Put a scan guage 2 on the dx port by the upper fuses while you drive and accelerate and see if the timing is too retarded while accelerating.

[Burntboot]

and if the van is new to you and you don't know the history.
Clear the codes and drive it.
Some of those codes could be from previous repairs that just weren't cleared.

Code readers are plenty cheap, even decent ones that allow live monitoring.
An excellent investment that will pay dividends for years to come.

[cgregs32]

Thank you for the responses! It gave me a place to start. I found out that these codes are OBDI. My 95 van has OBDII and only has code its P0171 (system-to-lean).
I am assuming the OBDI codes listed above are old. I am going to reset them and see if any more arise.

I am having a bit of confusion why OBDI codes are present in the first place. should they match with OBDII codes?

I am going to look further into the system-too-lean issue. If anyone has some insight on this specific to Previas and could point me in the right direction, that would be much appreciated!

Almost forgot to illustrate the issue I am trying to resolve.

Symptoms:
My van has a shudder when accelerating at highway speeds. The shudder is more pronounced when driving uphill at slight acceleration. If I increase the RPM's to almost floored, the issue does not persist.
The issue has created a strange driving habit of going between costing and high rpms in order to prevent the van from shuddering.

It must be related to the P0171 code. I am going to attempt to troubleshoot this issue myself, hopefully with your help :). Will post with further info when found. Thanks!

[cgregs32]

I found this thread, matches my symptoms almost exactly: https://www.toyotanation.com/forum/85-previa-forum/393867-97-previa-stutter-hesitation-fuel-pump.html

I would like to replace the things listed in this post to see if it cures my symptoms. I have never done any of this work, but I have always wanted to see what the top/side of the engine looks like.

I am not entirely sure what parts to get, input is appreciated. I know people are particular about their spark plugs



distributor oil seal?
I have no Idea what this is
cap
rotor
wires (https://www.rockauto.com/en/moreinfo.php?pk=946581&cc=1278244&jsn=544&jsn=544) + spark plugs (https://www.rockauto.com/en/moreinfo.php?pk=69491&cc=1278244&jsn=479)
Great video (https://www.youtube.com/watch?v=4oci1qijSt4) on how-to
any recommendations on which brand plugs?
Ignition coil


Bigger items to look into
- Fuel pump
- Fuel filter
- O2 sensor

[Burntboot]

I didn't even catch the '95 part and indeed OBD1 codes on an OBD2 vehicle is strange indeed, perhaps best to avoid that shop in the future??

What I know of lean codes fits in a thimble, but it is my understanding that #1 cause is a vacuum leak, #2 cause is lazy O2 sensor

[Burntboot]

Regular maintenance items are always a good idea to bring up to date but if that doesn't solve a known issue, then proper diagnosis is the next step.

Distributor seals usually involves an O-ring on the housing and an annoying external, drippy type leak.
(I have seen internal failures that allow the cap to fill with oil, but thats not really a Toyota issue)

Spark plugs should be as spec'd by Manufacturer.
I really like Nippo's, with NGK's a very close second.
But I would tend to hold off on the bigger items until they have been assessed (F/pump, coil) as I wouldn't expect those items to cause the symptoms listed
Usually when Fuel Pumps fail, they cause problems at higher speeds (flow)
Coils will usually cause spark problems, often when under load, and usually deteriorate with longer run times (more heat/more problems)

All sorts of things CAN cause midrange drivability problems and that is why the diagnostic process is so important.

[cb97alltrac]

I've changed 2 previa fuel filters; on the drivers side about half way back, not likely your problem but not too difficult to change. Just make sure you don't have any fuel leaks after changing!