Wouldn't Downshift, Gauges Oscillating, Now Won't Start

Wouldn't Downshift, Gauges Oscillating, Now Won't Start

2003 PreRunner
259,000 miles
Had alternator replaced at 20K miles.

Valve cover gaskets replaced Jun 28, prior to 600 mile trip to Northern Calif.
Problems started around July 1.
Check engine light on.

From standing stop, lugged due to staying in high gear.
Therefore, coming to stop, I would put in Neutral, then shift to Low or 2nd to go again.

If I left it in high gear, it would completely stall/turn off when stopping at intersection.

When it wouldn't downshift, the temp gauge was fluctuating wildly. Other gauges functioned normally.

I replaced the radiator a few days ago due to a split in the seam, although the engine never overheated.

Yesterday, engine just quit on me just as I arrived home, without any apparent lugging.

Last night I could not get it started. The engine turns over but will not start.

I suspect an electrical/electronic issue due to the simultaneous temp gauge behavior when the transmission was problematic and when the engine died on me. This was occurring before I replaced the radiator.

Took to Toyota dealer for diagnostic about 2 weeks ago and they said the transmission needs to be replaced, and that front O2 sensor needs replacing.

1. Could this be related to changing the valve cover gaskets? (Eg., sensor wires displaced and shorted out by contact with manifold.)
2. Is it possible it could be the ECM? How can I rule this out? Note the dealer diagnostic didn't say anything about this.
3. Could the O2 sensor be the culprit? Could that be causing problems with the transmission?

Thanks everyone, this is my first post on this forum. My current daily driver is my 2017 4Runner and so most of my posting is over on that forum.

Cheers!

 

It sounds more like the underlying issue is the engine dying at low rpm. Kicking it into N raises the rpm slightly.

Have you serviced the transmission before? Changed the fluid (drain and fill, etc). You don't quite sound like a DIY'er so you may want to get a second opinion from an independent transmission shop before taking the dealer's word that it needs to be replaced.

For the stalling - I'd start by cleaning the TB and IAC, and testing the IAC and TPS. I'd also be looking for any vacuum leaks (or just replace your vacuum lines outright- they are old enough to vote). When were the coils, wires, and spark plugs last replaced?

Edit:
I should probably add the entire air and fuel delivery system.

Air filter, MAF- good and clean?

Injectors? Are they original? MotorWest for new injectors.

Fuel Pump and filter?

I'm assuming v6, but you left the engine details out.

 

Thanks Andy.
Yes V6.
Everything original except for the alternator that I mentioned and of course the plugs and cables.
Old enough to vote, lol.
I don't 100% trust computer diagnostics so the fact that the dealer didn't find issues with the items you mentioned doesn't mean much to me. I think that one problem can cause the computer to not pick up other problems.
Yes an independent tranny shop, great suggestion.
Like your methodical approach.

 

Those things are really general maintenance items, they all could be "just within spec", contributing to the larger issue. I doubt a single one would be the smoking gun that fixes everything. But at 260k- you're going to need to tackle quite a few things. And yeah, the exhaust sensors should also be addressed as well.

As you start working through all this, it's worth mentioning: these 1st gen trucks are picky about what parts you use. Auto parts store parts generally cause more issues than they solve. But knowing which brands are ok to use will go a long way. Denso is a safe choice for things like the exhaust sensors, coils, plugs, etc.. Other things like the IAC or TPS - stick to OEM (buy them online from a trusted source, Amazon and ebay are full of fake parts).

 

That is great information.

Working through all of this.

 

Depending on your Toyota dealer so many techs are really clueless when it comes to vehicles this old.( As told by my Dealer service Manager)

From your description it sounds like you might have an electrical issue low system voltage could be from any number of issues .

 

Thanks for the input.

A reliable independent mechanic had it for about a day and a half. He reckoned it was an electrical issue, and sure enough he found:

1. Ground short in main electrical harness. This made the ECM go haywire and somehow this prevented the computer diagnostic tool from recognizing the second problem, which was that:

2. There was a fuel sensor was malfunctioning. I am not clear on the exact name of this sensor or what exactly it does, but guessing the air-fuel ratio sensor?

Bottom line is that the truck is running sweet again, back to its old self.

But I feel something is missing when the dealer can tell you that you need to do a replacement of your transmission for $4500, and it is just not true. Like there should be some sort of redress or penalty for that.

A friend always tells me that there are fewer and fewer real mechanics these days, and that the dealer mechanics are often "part replacers" ie. replace this part and that and see if it works, rinse and repeat.

(No offense to any dealer mechanics that may be reading this.)

Well thanks again everyone ! ! !

 

Glad you figured things out

 

It set me back $650, but that is a sight better than $4500 in my book!