I need some help! I've got a 2000 4Runner, 3.4L, Cali emissions. Currently, it's got 258K on it. The plugs and wires were replaced at 210K (NGK replacements for both). At 213K, the fuel pump and fuel filter were replaced. At 213K, I replaced the cats with Walkers and the A/F and O2 sensor with Denso units.

About four days ago, it had a hard start on a warm engine. Immediately, the CEL came on. P0171 and P0300. I replaced the MAF (Denso), gave it a test drive, and got the same codes.

I used some carb cleaner to look for a vacuum leak. When the carb cleaner got close to the PCV Valve, the engine stalled out. I replaced the PCV Valve (microguard), PCV Valve Grommet and the vacuum line between the PCV Valve and the throttle boday. I also unhooked the battery for an hour or so.

It was hard to start and idled rough. I drove it about six or eight miles and got it to operating temperature. No CEL. Once I got back, I turned it off and then checked it. No confirmed codes, but P0171 and P0300 were pending. I started it, again a hard start, and it immediately idled rough and stalled out. I can get it started, but it won't idle, and it's running rough.

I do have an exhaust leak between the rear cat and the muffler. It is small (I need to swap out the gasket) and it's downstream of the second O2 Sensor.

Any help would be appreciated.

 

What year and model?. If its a 3.4L with updated injectors, that would be my next suspect since you've changed a few items already, check every rubber for cracks and vac leaks between MAF and intake, I would use a OEM PCV, aftermarket PCV's can leak vacuum. Your idle should go up with carb cleaner or propane if a leak exists.

 

2000 SR5 4 wheel drive with California emissions system.

When I got near the PCV valve with the carb cleaner, it stalled out.

 

Ya the 99+ models got updated injectors that can cause issues, if you have a scan gauge you can see the LTFT/STFT, Load to help determine if it's running lean, or pull the plugs. eliminate all other possibilities and then consider the problematic updated injectors as a likely cause, usually it will identify which injector is the cause though. Again I wouldn't trust a aftermarket PCV or 20 year old vacuum hoses, you need to bend and flex all intake and vacuum hose and pipe to see the cracks if they are present or pressurize the system with a leak tester.

 

At the moment, it won't run unless I stay on the gas pedal. And even when I do that, it runs rough as hell.

 

Double post

 

Could be many things, injectors are a common issue like I said.., what denso MAF? #197-6020, was it a Denso Japan or counterfeit. Maybe TPS failure, you will have to dig into it further so we can help. And Cali spec emissions use a special AF denso sensor, not sure if the correct part # off hand

 

MAF was a Denso 197-6020 that I bought from Summit Racing.

I replaced the TPS in 2019 at 212K with a new one from the local Toyota dealership.

My OBDII reader is a bluetooth thing and I've been using the OBDII Fusion app on my iPhone. Like I said, at the moment, it wants to stall and die when I get it started. And even if I stay in the gas, it runs rough as hell.

 

Edited above resopnse for Cali spec AF sensor^.

Sounds like a completely failed or unplugged sensor for fuel or spark, timing off, or a huge intake leak. If it's injectors or spark you would need to drive it for a 1/2hr or so to identify which cylinder is miss firing, leading to the conclusion it is spark or injector on that problem cylinder and not fuelling sensor related. Could also very likely be the coolant temp sensor for the ECU fuel mixture, not the gauge sensor for the dash, there are 2 sensors.

 

I fixed the exhaust leak this evening. After putting the new gasket it, it fired up (took a little longer than normal) and seemed to idle fine. The CEL was on. I let it idle for 20 minutes or so. The CEL went off. I took it out for a test drive, some surface roads, some highway. On the way back to my buddy's place, I stopped and got gas. It was a very hard start, followed by rough idle and a CEL immediately. It drove fine to Ricardo's house, and idled just fine for a few minutes in the garage. I shut it off and pulled the code - still a P0171.

While on the highway, I did manage to get some data.


Idling at stop light:

STFT - 6.3%
LTFT - 39.1%
Calculated Load - 20
RPM - 607

On the highway at 60 MPH:

STFT - 1.6%
LTFT - 39.8%
Calculated Load - 34.1
RPM - 1970

Idling at gas station:

STFT - 4.7%
LTFT - 39.8%
Calculated Load - 15.7
RPM - 692
MAF - .5 lb/min

 

What are you using to measure LTFT & STFT, did't think LTFT could adjust more than 20% +or- so the parameters might be incorrect for the application, either way its saying its dumping a ton of extra fuel indicating intake leak or failed fuel monitoring sensor, this makes me wonder if it is the Coolant temp sensor the ECU uses to adjust for cold start ups, you should be close to 0% at idle and maybe 12-14% at cruise 70mph, 8-10% at 55mph under steady load.

 

I'm using a bluetooth OBDII reader and OBD Fusion on the iPhone.

My plan is to pull apart everything between the air filter box and the throttle body and look it over the next chance I get to work on it, unless I come up with a better plan.

Where are the ECT sensors, and how much of a PITA are they to change out?

 

You only need to worry about the front 2wire ECT sensor that the ECU uses to richen up the fuel mixture when cold, it is located under the passenger side fuel rail where the cross over pipe attaches to supply fuel to the driver side fuel rail at the front top of the engine. The rear temp sensor is 1 wire and only used for the temp gauge in the cluster. See post #15 for the parts required and if you dig around you will find a post with torque specs. Hopefully between your post here and T4R you will get some good suggestions, make sure to let us know what worked for you. I don't think your OBD readings are correct for LTFT something isn't calibrated properly for our engine, does the TPS range from 10%-75% out of curiosity not related to your issue. And did you pull the boots off the coils and check the connection between these items, it's a easily over looked connection. IAC stuck open maybe causing a vacuum leak?

https://www.yotatech.com/forums/f2/n...erence-232826/

 

TPS? I don't know what that is or if my scanner can pull it.

The Freeze Frame for the DTC said it was running on closed loop and that the information was coming from the AFR sensor.

 

Throttle Position Sensor, TPS should range from 10-75% approx. Did you check the crank pulley as suggested on T4R, if you have a bore scope you could also pull the upper t-belt cover and check the crank rotor to see if it's missing any teeth and check that the timing all lines up using the 0*TDC on the lower timing cover to rule out possible timing issues. Again running so rich seems odd, either missfire, big intake leak, or overfueling for some reason. Ever dig into the ECT or spark related items?
that's good you want to be in closed loop

 

I checked all of the belts - some of them were loose. I have not pulled the plugs to look at them yet. I'm debating about replacing the ECT. The next opportunity I get to work on it, I'm planning on pulling and cleaning the throttle body and the IAC.

Any chance it could be the AFR Sensor is trashed?

 

The 3 visible accessory belts are not associated to this issue, but there is another timing belt behind the cover, it needs to be aligned to the timing marks, and the Cam and crank sensor and crank rotor need to be working and complete. The AF sensor usually fails the heating circuit and the reading can fail or be off causing an issue yes, but your in closed loop so it makes me think your AF is working, but can't rule it out as I'm use to the Fed emissions with just O2 sensors