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Discussion Starter · #1 · (Edited)
Hi guys. I'm a newbie here ... sure hoping you gurus can help me figure out which sensor is causing a CEL on my daughter's '95 Tacoma 2.4 liter 4-banger. I did some searching, but didn't find an answer.

The truck only has 70K on it. It's clean and tight and well maintained. She uses it to commute to the university every day. Her check engine light came on last week. No obvious symptoms other than it has become a little difficult to start, i.e., instead of starting with just a tap of the key, when warm, it often takes more cranking before it'd catch.

I had the codes read: "P0170: Fuel Trim Malfunction Bank 1." Now I'm not sure if it matters, but if you look at these two read outs, you'll also see it also says: "Catalyst: not ready," and "Bank1 Sensor2 Short Term Fuel Trim 99%."

This weekend I opened the hood: I unhooked the battery to reset the ECU. I put in a fresh set of NGK pugs and a new air cleaner (just in case). I shot intake spray cleaner on the MAF sensor and inside throttle body, with the butterfly held wide open (both looked quite clean inside). I sprayed cleaned the EGR valve (on the top of the valve cover). It breathes fine. I checked EVERYWHERE for split or disconnected vacuum hoses -- none found. I inspected the connections on all the sensors that I could find, including the O2 before and after the catalytic converter.

I hooked the power back up. Then I hit the key. First tap, it started instantly. Revved nicely. Very crisp throttle response.

Backed out of the driveway. As soon as I put my foot into it, it stumbled. I drove it a few miles, and noticed a real dead spot/stumble between 1250 and 2750 RPM. It'd rev to near redline okay, but a fast tip-in of the throttle while loping around at low revs made it stumble.

Crap -- I've made it worse than it was before!

I came back, inspected everything, and then went for a longer drive. It started to improve (could be a few different reasons for this: it cleared-out the spray cleaner; it runs better warm; or the ECU started to "learn"). It's getting better, but it's still not right -- I'll call it 85%. It has a distinct "stutter" around 1200-1800 RPM when you gas it. And at WFO throttle, pulling a hill in 3rd or 4th in the high rev range, it has a misfire.

The check engine light has not come back on -- yet -- but I've sort of run out of ideas. I hate to start throwing parts blindly at this thing. These are the parts I'm considering as culprits:

1) Fuel filter?
2) Injector blockage?
3) O2 sensor malfunction?
4) Engine coolant temp. Sensor?
5) Throttle position sensor?
6) Mass air flow meter?

Note on #5 and 6: I called the local Toy dealer to see what parts they sell a lot of. They said they rarely sell either the TPS or the MAF sensor, let a lone carry them (they wanted $700 for a MAF!).

Anything ring a bell with the P170 code?

Tips are appreciated, and thank you in advance. :)

· Registered
7 Posts
Discussion Starter · #3 ·
Thanks for the link. I didn't know you had to use electrical contact cleaner for the MAF wire, but it makes sense. I had *assumed* an approved throttle body cleaner would be safe for all components on the intake side. That's what I get for assuming. Guess we'll see what the next 50-100 miles brings.
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