1995.5 Diagnosis Help!

Hello,
I put off this post for many months because I wanted to make sure I did the most I could before posting a thread. I wrote what the problem is and everything i've tried up until now.

Problem:
I have a 1995.5 Tacoma 2.4L 2RZFE 4-cyl manual, the more recent month model, and it stalls on a cold start. It only idles when I revv it to warm it up and it is a very rough idle; the whole cab trembles.

Its expired registration and basically trapped in the back yard and would take a a couple hundred dollars just to drive it in the street legally, which im trying to avoid since it has issues at the moment.

Has a OBD-2 port near the gas pedal but doesnt throw a code. I even bought a mini-vci device to hook up to truck to Toyota Techstream but the device wasn't compatible. I spent alot of time trying to make techstream work but it doesnt. Various "Toyota specific" code scanners apparently wont work on the 1995 Taco according to the vendors I emailed.

What I tried with internet research and the factory repair manual:
1.) I started with checking the EFI system. I replaced and calibrated the TPS sensor. All specs are good according to manual.
2.) Thoroughly cleaned the throttle body.
3.) inspected Idle Air Control valve(IAC), passes all internet and factory manual tests.
4.) Inspected and cleaned Exhaust Gas Re-circulation Valve (EGR). Checks out good.
5.) Replaced the Engine Coolant temperature sensor.
6.) Replace the Intake Air Temperature Sensor.
7.) Replaced Mass Airflow Sensor with brand new one.
8.) Had the ECU "repaired" at a mechanic shop. A family member did so the exact details of what was wrong with ECU are blurry, something about a bad circuit that was repaired. He's an ex-mechanic and insist it is not the issue.

Background: The car had 2 tuning devices installed when we bought it, namely, the LC-2 Lambda Air/Fuel Ratio Sensor Controller and the Apexi VAFC-2 Air Flower converter. The car ran fine with the devices installed but we clipped them so as to pass smog check, a short while after the car began to have the issues mentioned at the beginning of the post.

Im honestly stumped, the issue seems to be related to anything involved in the closed circuit cycle the car has when its a cold start. I'm beginning to suspect that the engine was machined to run rich or some other permanent modification like that.

Anyone have any idea? Any past experiences? Also, the parts for this car are so hard to find cuz of the year.

 

Welcome to TW

 

Does it have spark, is it getting fuel? Go back over and cover basic stuff.

Why did it have tuning stuff on it, was it turbo'd?

 

I would check basics stuff like Sebz13 said. Fuel pressure, spark, spark plug wires erc. There’s a few things to check even before trying to check ECU, replacing mass flow sensor and stuff like that.

 

I gotta wonder just what else was done to run those extra controllers ??

I hope you just did not cut the wires but removed them in the correct fashion.

I wonder is this the reason the OBII system does not connect ??

If you create a code does the light come on?

Guessing here poor connection at the IAC or coolant temp sensor you did replace the Coolant temp sensor not the sending unit for the gauge ??

Once the engine is to operating Temperature does it smooth out and runs fine??

How long has this adventure been going on( months) Ethanol blended gas breaks down fast might be as simple as bad gas ?

Of course a repaired ECU would never be the problem when asking the people that fixed it.

Back to the basics

 

I'm going to guess the airflow converter was being used to allow them to use bigger fuel injectors. I would check and see if it has OEM injectors or not

 

Also look at the TPS

 

Yes, all the spark plugs work. I’ll look into the fuel pressure next this weekend. Good looking out.

 

Another good lead, I’ll look into checking if the fuel injectors are modified.

 

we straight up clipped the wires on the devices. According to other blog posts it is fine to do that since the controller only splices into the original connections, so the wires “tapping” into the original can be cut.

As for what the previous owners changed, I researched both devices and apparently very little has to be changed on the truck to get them to work. But that doesn’t mean they didn’t change anything, I’m checking the fuel injectors next.

The car does NOT run smoothly when it warms up and idles. The gas has been there at least a year, Mabe more. Would a car stall because of gas? Then again, it doesn’t stall when warmed up...

 

You may want to check for vacuum leaks around injector orings or intake manifold on cold startup. As engine warms up, gaskets, orings and metal parts expand possibly sealing off the vacuum leak making it run better. Just a thought and very easy to check.

 

Hello, Just an update. I made a fuel pressure test and got mixed results. When I turn the ignition key “on”, but don’t crank that starter, there is no pressure showing on the gauge, I can’t even hear the fuel pump at that point.

However, when I start crank the engine and start the car, the fuel pressure is within range( reads a constant 40, range is 38-44psi). The pressure increase to about 44psi when the revs drops during rough idle( the revs drop then increase).

and when I perform the leak down test( check if pressure drops after engines turns off), it actually doesn’t drop but increases slightly when I wait a couple minutes.

I was hoping to get a straight low pressure or higher pressure reading, but that isn’t the case. Does this sound familiar to anyone? All injectors are stock by the way.

 

Your pump only turns on when cranking or the engine is running .

Not like the older models that turned on in the run position

 

Hello again, long past due update. I half abandoned the project but I’m back at it.

progress:
1. replaced fuel filter
2.replaced distributor cap
3.new spark plugs
4.patched a an exhaust leak on the exhaust pipe, right after the first o2 sensor and right before catalytic converter.
5. removed catalytic converter, flushed it out with water and confirmed it allows airflow to pass through.
6. Chopped off muffler on the suspicion that it was clogging the exhaust, end up being very unnecessary.
7. Lastly I thoroughly inspected for vacuum leaks wherever I saw a cracked hose and by spraying carb cleaner.


I’m thinking of going to check the Crank Position Sensor next because of a random suggestion I got.

If anyone has ideas I totally welcome them.