Hello,

I have a 95.5 2wd Tacoma 2.4L 2RZ. Long story short, I was having some hesitation / bogging so I started checking the basics. To date, I have done the following:

- Cleaned MAF sensor (signals look good, about 3.2 g/sec at idle, about 12 g/sec at no-load 2500 rpm)
- Replaced fuel filter
- Checked fuel rail pressure (about 35 PSI with vacuum to regulator, about 45 PSI with vacuum disconnected)
- Replaced spark plugs, spark plug wires
- Replaced distributor cap and rotor.
- Replaced front O2 sensor (bank 1, sensor 1)
- Tested EGR valve with vacuum hand pump, it works, not sticking. By works, I mean if I put vacuum to it, it kills the motor immediately.
- Looked everywhere for vacuum leaks.
- Checked grounds
- Checked PCV valve, not clogged.
- Replaced fuel injectors with these:
http://www.ebay.com/itm/Toyota-Tacoma-95-99-2-4L-2RZ-2RZFE-Denso-4-hole-upgrade-fuel-injectors-/271507095404?pt=Motors_Car_Truck_Parts_Accessories&hash=item3f37157f6c&vxp=mtr
It runs great when already moving, but it has very bad intermittent stumble / hesitation off the line. It is to the point where it won't really move, and I have to clutch it and blip the throttle several times to get it running right again. It sounds like it is about to stall.

The only code it has thrown is P0170, fuel trim malfunction. At idle, the fuel trim is negative 15-20%, meaning the ECU is trying to correct for a rich condition. If I unplug the front O2 sensor, the fuel trim moves to + 20%, which makes sense that is thinks it is super lean and is trying to add fuel to correct.

When driving, fuel trim seems OK, it varies with throttle position, and when off the gas and coasting it usually hovers right about 0%. When I stop though and let it idle down, the trim still goes back to negative 15-20%.

I'm completely at a loss, and am ready to take it to the dealer. Anyone have any experience with the Ebay injectors? I talked to the guy selling them and he said he has sold hundreds for the 2RZ and not had any issues.

Thanks,
Josh

 

Did you pull the EFI fuse or neg battery cable to reset the ECU?
Did you use a Denso O2 sensor? We have found other brands don't play nice.
Are you sure all the injectors are firing?

I'd give cleaning the MAF wires again.....Mass Air Flow Sensor Cleaner is what works for me.

Welcome to YT!

 

Yes, I have pulled the battery ground and the EFI fuse to reset the computer several times. It seems like something is forcing the trim to large negative, or it is reading incorrectly.

Yes, I used the Denso O2 sensor from Napa, with the connector.

All injectors are firing. I have checked by listening with a long screwdriver, and also if i inplug the injectors one at a time, I can hear the difference in idle when the cylinder stops getting fuel.

What else could cause too much fuel at idle? BTW, the idle is smooth and sounds great, not like it is struggling. I have a OBD adapter and the Torque app, so if any other info would help I can pull it.

I have an appointment at the dealer on Tuesday but if i can figure it out, I would rather save the $$!

 

Have you tried putting the original injectors back in? The dealer may question the 'upgraded' injectors if they are not the original part number.

Double check for any holes or cracks in the air cleaner box/intake tube/vacuum leaks after the MAF. The slightest amount of unmetered air can cause havoc.

Just noticed the last thing in the P0170 diagnostic is the Engine Coolant Temp Sensor that feeds the ECU. Might be something to check out.

 

check for vacuum leaks. if you can get it to idle while you are under the hood, spray a tiny amount of brake cleaner around your vacuum hoses. if it suddenly changes rpm's or dies, you know that's where the leak is.

 

If it was an air or vacuum leak, wouldn't that cause a lean condition and the ECM would be trying to adjust to positive fuel trim? I can pull a vacuum line and watch the trim go positive on my scanner, so I'm pretty sure that is the case. I am getting too much fuel at idle somehow.

I was hoping not to go the route of re-installing the old injectors, especially since the original injectors have 275k on them and look like they were pulled out of pond. I would have to go get them serviced if I wanted to put them back in. I was also thinking that it could be the injector flow rate, providing too much fuel and the ECM could not shorten the pulse time enough at idle, but looking into the part numbers further, the new injectors actually have 10cc less flow rate, with a slightly higher impedance. I would think that such a minor change could be accommodated by the feedback control on the ECU.

Injectors (top is new, bottom is stock):
https://plus.google.com/photos/11590...I3098aWh6yr2QE

 

Do you think the engine coolant temp sensor could be malfunctioning and causing the ECU to command more fuel to warm up? Or the thermostat sticking slightly? At full warm up the coolant temp never goes above 181 deg F. Just a thought because I know some EFI systems enrichen the fuel until the engine gets up to proper temp. Not sure what the temp is on a Tacoma though.

 

Normal operating temp after warming up: 176-203F per FSM.

Pull the ECT sensor and see if it has scale build up on the probe. If so, carefully wire brush it off. It could be sending a wonky signal when cold.