1997 Tacoma starts, revs, dies.

Hi,

My '97 Tacoma is causing me pain. It's been getting worse.

For awhile, it would start and run poorly. Long term fuel trim was like 30%! So I knew it was super lean.

I found vacuum leaks, after pumping cigar smoke into the intake, including a ferocious one from the EGR vacuum solenoid, plus one from the PCV. I replaced the EGR solenoid and the PCV valve and grommet. I believe all vacuum leaks are fixed.

So, it got worse.

It starts but will not idle. Like, it runs for 3 seconds after releasing the key then stops. During the 3 seconds it's running I hear no misses. It sounds good.

I checked for fuel, by removing the hose from the return circuit, and it's pumping fuel like crazy through the return (all over the alley). Of course, there may not be enough pressure at the injectors to fire, but the rate of delivery is pretty impressive.

I unhooked the battery so the truck's computer would be forced to relearn everything; no difference.

I unplugged the MAF so the truck would go into fail-safe mode and run poorly. It made no difference.

Could it be the fuel pump? Where would I attach a fuel pressure guage?

Any other ideas?

thanks

T

 

Could be a camshaft or crankshaft sensor or the wires to it

 

If your certain there are no more vaccum leaks (vac leak was my first thought) it sounds to me like a fuel injector problem, or fuel pressure regulator problem.

 

I just bought a fuel pressure tester off Amazon, let's rule out the fuel pump for sure when it comes tomorrow. I also ordered a fuel pressure regulator, the one that's on there doesn't seem to change the flow rate between vacuuum on and vacuum off.

 

Check for cracks in the air intake tubes?
If you use throttle to keep it running for about a minute, will it hold idle after that?

 

I have a suspicion... I've been reading threads about bad capacitors in the ECM. It fits the profile of what I'm experiencing.

Tomorrow night I'm going to pull the ECM out, crack the case, and see if there's a mess in there. I've replaced electrolytic caps in ham radios before. If there's some bad ones in there, I'll try that.

 

OK, I pulled the ECM out of the truck tonight... everything inside the ECM case looked absolutely pristine. No indication that the thing is 27 years old... none of the Caps were swollen, no sign of leakage onto the circuit board, nothing looked bad. I was about to give up and put it back together when, under high magnification and very bright light, I noticed discoloration on the negative leg of one of the 100 uF caps: corrosion. It's gotta be a leaky cap.

I will ATTEMPT to replace it tomorrow. I'm not touching any of the others (although prudence would dictate that they are about to go bad too), just the known-bad one. "First, do no harm."

 

Well, I had a heck of a time replacing the one capacitor. It looks like there's a micro-resistor between the 2 poles, soldered to the underside of the board... which precludes removing the 2 legs from the PCB board. i had to solder the legs of the new cap to the stubs of wire left after I cut the old cap away. It had definitely failed...

Anyways, it's a hack job, but it fixed nothing. Either the problem resides in another one of the caps, which I am loathe to try to replace, or it's something else entirely.

The search for an answer continues.

 

Update: removed the throttle body and IAC Valve, both of which were full of tar. Literally. Cleaned everything, and replaced the IAC valve. Reinstalled.

No change. Starts, idles a sec or 2, dies.

 

My problem was the IAC. Would start then die. Cleaning it was not good enough but when I replaced it, then it worked. Not to say that's what you need to do, because it sounds like your engine issue is a bit different than what I had.

 

I did replace the IAC. I've had all sorts of cars go from balky to great doing that, especially Volvos, but it didn't fix this. When I was cleaning the throttle body yesterday I was certain I had found the problem. I couldn't believe how much gunk was in there, it took almost an hour of spraying and wiping and spraying and wiping to bring it around.

The one known error condition is, still, bad capacitors in the ECM. So I swallowed hard the other day and bought a remanufactured unit. We'll see when it comes. Fingers crossed...

Fuel pressure and delivery seemed good but I'm going to test it with a different gauge.

 

She's up and running.

New fuel pump and filter were needed (low pressure), but did not fix. Also needed a new MAF. There's a Hitachi unit in there now.

Way too much dinking around, way too much expense, but it's nice to have my old truck back in service. A rust-free 1997 is worth saving. Rock steady idle at 850 RPMs and better acceleration, too. Still a dog but does the job.

I think I'll treat the old gal to a Rustoleum turbo paint job in the next few weeks. Maybe I'll post some before-and-after pix.

 

So do you mean it was the MAF? I always hear bad things about any aftermarket sensors. How did you determine the original was bad?

 

The Chinese MAF sensors are junk. Always. Some I have seen for other makes seemed to just be a fake signal generator.

 

Once the system finally had adequate fuel pressure, it still wouldn't run. Unplugged the MAF again, and it ran like shit. New MAF, runs great.

 

what brand of MAF did you get?
i peeked at the OEM Yota Maf for 5vzfe and OMG

 

Are all aftermarket ones Chinese? If not, how do you identify non-Chinese ones, and which ones are ok? My understanding has been that all non-Toyota or non-OEM supplier sensors don't work right.

 

Was going to suggest testing the MAF…if you unplugged it and saw no change, then that means it was doing nothing.
A snap throttle test while monitoring output peak voltage would have likely diagnosed it at failed.

 

what mass air flow sensor did you purchase?

 

Just wanted to bump this up, I’m in a similar situation, and would like to see more on the subject.