New user w/ perplexing problems

Injectors? How many miles? You really need to be able to read the code(s). Good luck

 

Disconnecting the TPS is not a good way to diagnose the problem because as soon as you disconnect a vital engine sensor the computer goes into a fail-safe mode (limp mode) and adjusts things like air-fuel ratio or ignition timing just to keep the engine running at the expensive of worse fuel economy and emissions. So just because the engine seems to run better when you disconnect the TPS doesn't tell you anything about whether the TPS is working correctly or not.

How did you install the new TPS? Did you use a feeler gauge and ohmmeter to set it at the correct angle to properly detect when the throttle is fully closed? The same tools are used to test whether the TPS is working correctly, so that should have been done before buying a new part.

The repair manual says, "If there is open circuit in IDL line, DTC P0120 does not indicate." P0120 is the code for a malfunction in the throttle angle sensor, but it seems to be saying this isn't set if the idle position open/closed circuit is open which is the condition you are creating when you disconnect the TPS, so it would not surprise me if you don't get this code with a code reader. The IDL circuit could be stuck open if you didn't set the TPS correctly when you installed it.

If the TPS is set/installed correctly and you still get a check engine light then it could indicate a problem with the computer, but this should be the last thing to suspect since they are usually pretty reliable.

I would suggest that you check your ignition coil in the distributor (or coil packs). It looked like a distributor in the video which I know were on the 96 3RZ-FEs and maybe 97 models. Visually check the coil and then check the primary and secondary resistance. Even if it checks out good it could still be bad when it's actually running. While the distributors were unique to these engines the ignition coil inside was used on several models from this time period. A used Denso ignition coil is a lot of times better than a new aftermarket coil, so if there's a good junkyard nearby you may be able to find a Denso coil with a matching part number. When the coil goes bad hesitation is sometimes a symptom. It's also something that won't throw a code.

 

If she has EGR I would disconnect the vacuum line to the EGR valve and retest.

The fact that this happened right after you hit the transition hard tells me that you jarred something loose, a connector, a wire, something... I second ArizonaBrians suggestion.

Disconnecting the TPS or any sensor as a diagnostic procedure can lead you to a false conclusion. There are redundancies built into the PCM to continue to allow the truck to run "just in case", not perfectly, but enough to get you home or off the road.

 

Mileage is around 178k if memory servers me right. I'm not sure what previous owners have done to it but I would assume everything that I haven't replaced is stock or at least close to it. I still can't get a scanner to connect and give me any codes, I've been working on it here and there trying to troubleshoot why I can't get a connection with the OBD port but I've just been really busy with other things.

 

Something I found pretty strange when I was troubleshooting the other day. I removed the EGR vacuum solenoid thingie and the fuel pressure regulator and tried cleaning them a little. When I reinstalled I forgot to connect all the vacuum lines before starting it up. It started and ran perfectly fine with all the vacuum lines disconnected was just idling higher. I went out under the hood and realized my mistake so I started checking the lines for vacuum. None of the smaller lines seemed to have any suction at least none that I could feel. The only line that had noticeable suction was the PCV vale hose which I could hear sucking pretty loudly from inside the cab. Even the vacuum hose that runs from that weird metal box between the MAF and the throttle body, then connects to the fuel pressure regulator had no vacuum suction that I could tell or feel

 

This would explain why it's shooting black soot and smoke out the back I assume. I was not aware that you needed to install the TPS at a certain angle, I will try looking into that info more. What does IDL stand for? Yes it is a distributor cap and button type ignition. I had been wondering if the distributor and button might need replacing. Thanks for all the good info gives me a few more things to work on. Where is the ignition coil located?

 

I think you're on to something with the EGR valve / solenoid. You can test it right on the engine if you have a vacuum pump. Not sure how good the access is on the Tacoma though... Never had to mess with mine but have dealt with them on Hondas. Hopefully the no com situation is not related to any of your problems but you really can't go further into that without an oscilloscope.

 

If your EGR solenoid is stuck open it would be constantly applying vacuum and make the vehicle stumble all over itself if not stall completely. When you disconnected the line the EGR would've resorted to it's normally closed position allowing the engine to run smoother. If you have a vacuum pump, disconnect the vacuum line to the EGR from the solenoid and manually apply vacuum. The vehicle should go from running good to stumbling showing a good EGR valve. That's hoping Toyota EGRs function like Hondas. It's been a while but I think your solenoid might be bad. Just going off memory so don't hold me to it.

 

Ok thanks for all the great info and advice guys!

 

There is hardly any vacuum from that hose because it is not connected to the intake past the throttle plate. I remember a few years ago someone started a thread saying how useless that vacuum hose to the fuel pressure regulator was because of this. Anyway, what you observed is probably normal.

IDL is the terminal of the TPS that detects when the throttle goes from completely closed to slightly open. The IDL to ground (E2) terminal will either be 2.3 kOhms or less when the throttle is fully closed, and infinite resistance (open circuit) when the throttle is slightly open. The computer will only use the IAC valve to control the idle when it thinks the throttle is closed (idle position). You are supposed to set the TPS, so that you get those resistance measurements (IDL to E2 terminal) when the throttle is closed and slightly open.

The ignition coil is inside the distributor. When you take the distributor cap off there should be a plastic cover that you remove and the ignition coil is behind that.

 

So I've been out in the garage today trying a few things y'all mentioned. I started off by adjusting the TPS as best I could manage. I watched a video of how to set the TPS but it was for a 22RE engine, I'm not sure how this compares to my engine but in his diagram it said E2 (1) was the bottom pin, which I'm calling 1. IDL (2) was next up. VCT (3) after that. Then the top pin being Vcc (4). I'm going ahead and just referring to them as 1 2 3 4 because I dont' actually know what the pins on my TPS are, or how closesly they match the video I watched of the 22RE. So the reading I got are as follows pins 1&2 1.192 kOhms. Pins 2&3 1.545 kOhms. Pins 1&3 546.1 Ohms. Pins 1&4 1.645 kOhms and Pins 3&4 were 1.782 kOhms. I don't have a feeler gauge so I just used a piece of paper and calipers, folded it a few times until I got my calipers to read about .84mm, then used this to slightly hold the throttle open. Not really sure if these reading are within spec so I'm hoping some of you pros can help me understand them better.

I also fiddled with the EGR some. I removed the vacuum line as suggest and applied vacuum to it and it immediately started to stumble and died like ArizonaBrian said. As I was doing this I started contemplating what ArizonaBrian was mentioning about how far down this rabbit hole I really want to go. Into diagnostics and troubleshooting etc. I know this little truck is in really good shape for its age and mileage and it does hold a good amount of sentimental value to me because it was a truck my mom and I bought together so she had something easier to get in and out of and I had a little work truck to haul crap with.

Taking all this into account I decided I'm not giving up on her and I'm in it to win it! I've been wanting a project car for a while and I'm just going to make this it. It's no 69' Challenger or anything I realize but it will be fun for me to tinker around with and learn a lot of things. Plus I have plenty of spare time on my hands so it will keep me busy here and there. Anyway with all that said I decided to take the bed off to get a better look at the tank and things. This is what I found...Let me know what you guys think!

 

Well I've made some decent progress and recent discoveries I'll go over just to keep things updated. First off, I got all my new parts installed, fuel pump(which was actually the entire assembly with the pump/sending unit/strainer), fuel filter, EGR valve, EGR solenoid, and MAF sensor. Got everything put back together after spending a few days cleaning all the intake/exhaust ports and intake manifold etc. No noticeable change in the hesitation or stuttering while on the throttle .

Today I met a guy here locally in my area that is known as the Tacoma guy! He is an awesome guy and says he's built like 400 different Toyotas over the years, so he's got quite the collection of old parts. He was nice enough to let me borrow some old parts he had lying around to try swapping them out and see if that would fix my problem. He let me borrow a ECM, distributor, and MAF sensor. Currently I have only tested the MAF and that had no affect. He needed me to take a picture of my ECM so he could check his cache and see if he had the right part. While I was in there digging out the ECM I thought...I've got this can of electronic cleaner, let me spray off these connectors to the ECM and see what happens.

So I did just that and resprayed my OBD2 port and let them dry out a while, then attempted to reconnect my scanner and see what happens. Well wouldn't you know it! My scanner connected, but still said there was no codes found! I then attempted to go into the live data and start the truck so I could post the live data results for you all, and before I could even get it started...the scanner lost connection . This has me wondering now if there isn't some sort of electrical issue I'm missing? Anyway just thought I'd update those interested and see if y'all had any other thoughts or suggestions. I'm starting to lean towards the ignition coil/distributor, but my distributor looks shiny brand new.

 

FINALLY! Just got done swapping out my ECM for the one I got from Tacoma guy! Everything seems to be running great! No more check engine light and my OBD2 port is working again. So I went ahead and got some pics of the live data just so you can analyze it and tell me if everything seems ok.

 

Wow that's awesome brother! The no check engine light was tell tale but new ecm was worse case. Glad you got it figured out!

The numbers look good to me except for maybe that MAF but it's possible the scan tool is rounding up or the vehicle needs to warm up more. Hate it when obd scanners use lbs/sec (or lbs/min) instead of gms/sec.

After she warms up what's the idle look like?

 

It was up to normal operating temp when I took the live data. I may be able to change the units on the scanner to metric, not sure if that will read out in gms/sec like you said but I'll give it a shot! I'm so happy I've finally got this little Taco running right again. Thanks to everyone how gave advice and suggestions along the way, its much appreciated!

 

For a MAF system they say gms/sec readings should mostly be close to the size of the engine in liters +/- and at operating temp at idle. Converted you'd expect 0.0053 lbs/sec. But the scan tool may not be expecting that many decimals for that PID so it might be rounding up to .01 as you're seeing. As long as your fuel trims stay good I wouldn't worry about it.

 

It would be interesting if you take the cover off the old ECU and check if there are any damaged components. Sometimes the old electrolytic capacitors go bad and can cause a problem.

 

Just changed the units to metric and the MAF was reading around 4.5 g/s. I will definitely be taking the ECM apart to see what I can see. Might even try to repair it or have it refurbished to have a back up on hand.

Also noticed while I was just checking live data that my idle seems to be a little above normal, around 1k or so. I never really noticed it because there is no tachometer on my dash. If that's all I have to worry about now though is a little high idle, I'm good!

 

So if I'm interpreting what you're saying correctly and my MAF is reading 4.5 g/s at idle, then it's getting to much air and running the A/F ratio lean? Any cause for concern with this?

 

The MAF procedure I mentioned isn't full proof. In fact in my experience the initial numbers (even after warm up) will be double the litre size of the engine and only after a long idling time of about 15 minutes will it go down to within .5 gm/sec +/- the engine displacement *on an optimal running vehicle*. You also want to make sure AC is off. At least it's not unmetered air - the MAF is detecting it - so your high rpm could be due to a slightly worn throttle body or something else. I would do a search here for elevated RPM as there's lots of info that you might find useful.