Help with a 98 tacoma with a 2.7

I am helping my neighbor with his 98 tacoma 4wd with a 2.7l 4cl.
His CEL came on and has stayed on.

It has a heavy shake during idle. It seems to run and drive ok.

I coded it and it comes out with p0125 confirmed dtc with a few others pending.

I opened it up and took a look at the plugs... he doesn't know much about cars and the guy he took it to was a shade tree mechanic who put autolite plugs in and barely screwed them in ;/.

I put ngks and gapped them properly and cleared dtc to check if it was the plugs. The dtcs went away for a short time maybe 40 miles then came back on, so i coded it again.

Same confirmed with same pendings, so plugs didn't fix it .

I don't want to keep replacing part after part on his truck, so i was wondering whats your guys opinion? I was thinking on maybe the o2 sensor bank 1 sensor 1 since that's what the Diagnostics heavily pointed towards.

Will post a picture below of the coded screen. Any opinions and advice greatly welcomed.

Thanks Guys.

JP

 

Scroll down to the Manuals section of this thread and there's a link to the Toyota repair manual in pdf form:

https://www.tacomaworld.com/threads...-thread-compiled-list-of-helpful-links.95271/

The repair manual will help explain what the root cause of any DTC is. The chart with all DTCs is in Diagnostics/Engine/dtcc.pdf.

P0125 is for "Insufficient Coolant Temp. for Closed Loop Fuel Control". Could the thermostat be bad, so the engine isn't reaching full temperature? The other O2 codes could be a symptom of this.

...but I'll add that there may be something lost in the translation regarding "Coolant" because the repair manual seems to only talk about the heater circuit for the O2 sensor for code P0125. So, if the coolant is the correct temperature, then maybe the heater circuit for the O2 sensor is bad or the heater is burned out.

 

OK I fixed the ETC and the 02 sensor, and code is now gone.
However it still misses/rough idles, and rumbles at higher speeds.


I checked the plugs,wires,coils,fuel injectors,maf, and none of them had any issues.
We also smoked checked the entire vehicle and no leaks.

The truck was taken into a shop for a blown head gasket before i bought it. They fixed it but am not 100% sure of there work.
My friend said the next thing he recommends is check timing.

Is there any other known issues that could cause this? There is no CEL or Pending codes on it anymore.

Thanks Guys.

JP

 

Anyone have some advice? It was still rough idling. So I decided to change the fuel filter and hope that may have been an issue. I also cleaned the injectors while i had them out. I wanted to check some of the sensor out while i was taking it apart and found the EGR temperature sensor and the the metal tip that goes into the EGR was completely black. Does anyone think that could've been the issue or one of them? And how do you test it off the vehicle?
Thanks all.

JP

 

IINM - if it's an electrical part, and you have the factory manual (available somewhere on this site) and a multimeter you should be able to test it. Parameters and methodology should be in the manual. I have the manual (digital) and could provide some specific sheets. Other than that, I have no suggestions...

 

A rough idle likely wouldn't be attributed to carbon build up on the EGR temp sensor. Not a bad idea to clean it off though. Usually when the egr temp sensor isn't functioning correctly it will cause the MIL to turn on and it's usually a P0401 or P0402, which are 'egr - insufficient flow' or ' egr - excessive flow'.

 

Hmm OK well no codes were thrown after fixing the ECT so I will clean the EGR sensor up and put him back in.


I came across a list on the internet of possible causes Let me know what you guys think. I have already done a few of them.

• Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)- I already Replaced Plugs wires looked good coils checked out fine.
  
  
  
  
• Incorrect ignition timing- I haven't had time to check timing yet was going to do that while putting things back on.
  
  
  
  
• Vacuum leak(s)-none found tested 2 times.
  
  
  
  
• Low or weak fuel pressure- Cleaned injectors, and installed a new fuel filter(have not tested vehicle since as its still apart I am going to cross my fingers and hope that could've been it but I really doubt it.
  
  
  
  
• Improperly functioning EGR system- Have not tested it yet. Do you test this with a vacuum pump?
  
  
  
  
• Defective Mass Air Flow Sensor- Cleaned and tested it by removing it while vehicle is running. It showed it was working.
  
  
  
  
• Defective Crankshaft and/or Camshaft Sensor- Not sure on these guys. I need to find out how to test them and will look in owners manual as you suggested.
  
  
  
  
• Defective Throttle Position Sensor- Also haven't checked it yet need to figure the testing procedure for this one as well.
  
  
  
  
• Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems- I Have not checked compression, head gaskets don't seem to be leaking and I don't think its valve related, but could be wrong.
  
  
  

Common Misdiagnoses

• Fuel Injectors- Cleaned them anyhow since they had to be taken off.
  
  
  
  
• Oxygen Sensor(s)- Seem to be working fine as no codes are thrown?
  
  
  
  
• Power Train/Drive-train problems- I don't think it was related to me replacing clutch as I was very careful to mark all correct reinstall marks.
  

Thank you guys for the help thus far. I really appreciate it.

JP

 

@98tacoma27

 

That opportunity will never happen again.

 

I am sorry but I'm not sure what you mean.

 

The pending codes relate to the up-stream O2 sensor. I've read somewhere (on the Internet, for what thats worth, ), that a bad 02 sensor can also trigger a p0125, not sure why. Therefore, if this were my truck, I'd replace the up-stream 02 sensor. Easy to do, but the sensor is pricey.

 

Would it code the engine though if it was a bad o2 sensor?

The CEL went away for the ECT sensor code after I replaced it. There are not any other pending codes and the CEL is not on. This is one of the reasons this is driving me nuts. I am horrid at diagnosing vehicles.

 

CEL does not turn on for pending codes.

So, you replaced the ECT sensor and no more P0125, correct?
Is the idle still rough?

 

Yes i replaced the ECT sensor and the code went away. Yes and it still ran rough during idle and at speeds like 45-50ish.

 

Bad idle could be the IAC valve (Idle Air Control) since you've checked for vacuum leaks. Have you cleaned it yet?

Brand new symptom? What about above that speed?

 

It doesn't do it when not idling, and only when it gets up to around those speeds.
I will have to check IAC tomorrow. It will be easy to do so because it still all apart on my bench.
I will check that and see.
Thanks for the help so far.

 

The EGR temperature sensor is strictly an emission test. The computer doesn't use the reading to control the EGR valve. More likely a stuck EGR valve if it were EGR related. Sometimes the EGR modulator will leak when it gets old and cause some EGR problems. I would check other things first before the EGR system, although it's pretty easy to check especially if you have it all apart right now. An EGR problem probably wouldn't cause a problem at 50mph.

Checking the IAC is a good idea. Clean it out. And you can test the solenoid part following the procedure in the repair manual. You should replace the IAC gasket when you remove it from the throttle body. Those screws are easy to strip. If they start to strip you can grab them with a small vise-grip and start to loosen them. It's probably good to replace with new bolts.

Do a compression check just to be sure the pistons, rings and valves are working correctly.

Check the valve clearances. The mechanics that replaced the head may not have check them real good.

If that all checks good, then check the distributor coil.

 

OP,
I agree with all the above, except the last sentence. DrZ's truck does have a distributor, but yours does not.
However, you do have 2 standalone coils in front part of the 2.7 that are very easy to remove/replace.
If you know someone with a similar truck (98-00 2.7) you could swap in his, just to see if it makes a difference,

- or - do a resistance check on each coil (s/b around 13,500 ohms)

 

JUST REPLACE YOUR EGR IF IT DOSENT WORK ILL BUY IT FROM YOU !!!!!


It'll work , have faith

 

I will have to do a resistance check because i don't have another person who owns a 98-00 Tacoma.
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The whole egr?? or just the valve??
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I went ahead and ordered a Iac valve as i found one at a decent price-but its not OEM i hope this doesn't come back to bite me in the A** but its what he could afford.

I will have to do a compression/valve/timing check next if the egr/iac doesn't fix it. I am hoping it does fix it because I am getting very tired of this sitting in my drive way, and am getting frustrated at it.

Again thank you all for your help.

JP