Losing power and shaking at 40mph

Hey all - I have a 2002 3.4L manual 4x4 with 140K miles. I've had virtually no issues with it until this year. I changed the timing belt, water pump and all the accessory belts first week of January. Also replaced shocks and struts and rotated tires. Everything seemed fine for a couple weeks, then I started losing power climbing hills at around 35-40mph. I get a bad all-over vibration and rattling noise and the truck just slows down. If it's not on a hill then it seems to mostly handle accelerating fine. But I live in western NC, so pretty much everywhere is a hill. If I get a running start going down hill to about 50-55mph, then I might be able to maintain 40 by the time I reach the top. Not a great way to drive and I have to avoid certain roads because of it.

I've been searching google and youtube relentlessly trying to figure out whats wrong but I can't find anyone describing similar problems. At first I thought it might be my trans but I have no problems changing gears, shifter is tight, etc. So I thought maybe it's an airflow issue. I cleaned the maf sensor and that seemed to help briefly but then it just got worse. So then I replaced the maf sensor and again it seemed like it was improving a bit but it's just worse now. My next step is replacing pcv valve simply because I read somewhere that if I replace the maf I should replace the pcv valve too. I'm hoping, but I don't think that's going to change much since what I've been reading is that mainly deals with idling (I don't know). I'm not getting any check engine lights except briefly when I first cleaned and then replaced the maf sensor. Otherwise the engine light is always off. My next guess is possibly the fuel filter...? I do get horrible gas mileage sometimes worse than others. I know tacomas aren't great on gas to begin with but for me a 20-mile round trip usually takes close to a quarter tank. I also have zero issues with idling. I can sit in the driveway and rev the engine all day long and its smooth, but as soon as I go anywhere and break 35mph it gets the shakes. It's never stalled but on occasion it does rev high for a second or two when I come to a stop, which it never did before. I'm not an experienced mechanic and this is the first time I've ever really had to deal with issues on this truck so I'm feeling my way around in the dark. Any info would be much appreciated since it's two months now that I've been dealing with this and can't figure out what's wrong.

 

You get 60 miles a tank???

Replace fuel pump for sure. Air filter, spark plugs and coils should be considered too.

 

Thanks for replying. Fuel pump or filter?

I did replace the air filter. Was thinking about spark plugs too but they were changed not too long ago.

 

When you floor it does it bog or stutter at all?

Fuel filter, coil pack/packs (could be pre stages not throwing a code yet), plug wires, plugs themselves, fuel filter, possibly something with the computer. It should be throwing a code though which in your case would help diagnose the problem


Edit: Also, when it shakes at 40 etc does the cel blink?

 

I try not to floor it, the more gas I give the worse it gets so I left off the gas. But I guess I'd say it bogs..? No stuttering so far. Fuel filter was my next guess. Fuel pump will require a mechanic cause I don't have the means of doing it myself.

No cel blinkage so far.

 

Whoops. Meant filter.

 

With the truck idling tap maf sensor lightly with the handle of a screw driver if the idle fluctuates the maf is bad. Sorry, that's all I can give you and good luck!

 

Changed timing belt......for shits ,pull 6 bolts from top timing cover ,rotate crank by hand and make sure timing marks are still lined up.
Curious,did you pin the tensioner to get the belt on or how did you get the belt on.

Next guess would be coil pack.

 

Pull the plugs and take a look at them

 

It's possible a cam jumped a tooth or two. I second the question on the tensioner.

 

If the cam jumped a tooth or two wouldn't that cause the truck to have trouble starting?

 

I would hook up a obd scanner anyways and check for codes. Sometime the light can burn out and has codes. There is also the historic codes that could be there but not posted as a fault yet. Sounds like you got the timing belt wrong. If it's just one tooth off it can still run. But usually it throws a code. Sounds like the truck is trying to adjust Fueling big time because of the retarded timing. If the truck does throw a code the timing will automatically retard 5 degrees and you will lose even more power. Those 2 factors together means that's a gutless gas sucking turd!

 

some times it has no effect on the way it starts and runs unloaded. Then you drive it in open loop and it all goes to shit! I had a van that would slip a tooth after setting up the timing belt with cam locks to ensure it was done right and we did it 3 times before having to put new cams in it. And when disassembled the head one of the gear teeth was broken inside on the cam end causing it to jump a tooth on start up. My mechanic(employee) was pissed he had done it 3 times and it was a G damn cam because my customer was mad "we miss diagnosed it" But in fact his timing belt broke because he didn't change it and he tried to blame us But that caused the damage to the motor. Well once we got the head apart and replaced the prts he had a hefty bill for labor and towing. Once i can prove it's not our shops fault or defective parts the customer has to pay the bill not us.

 

Damn good question there also. I always use a new kit that has all new parts and a new tension that's per-tensioned with the pin in it. If you have to re-use the old one, We remove the tension-er and put it in a vise and compress it down slowly and then use like a ground down Allen wrench or similar hardened thin piece rod shaped metal.

 

not always

 

Just curious, did you find the problem?

 

My 2002 did the same thing... I thought my transmission was going out. Changed out the plugs and wires and it cured my issues.

 

Thanks for all the responses, and sorry for the long delay in my responding, I've been busy as hell the last several weeks.

I still haven't solved the issue completely though it has improved some, and other issues have developed.

I changed all the spark plugs with nkgs. Also changed the wires and the fuel filter. It's still doing the same thing but it's not losing as much power as before and not shaking as bad. I can get up hills now and its fine 85-90% of the time. I took it to a mechanic about 3 weeks ago (who seems to have a good reputation around here) and he said the timing was about perfect. He said it runs as good as any other tacoma he's drivin (lol). But I don't think he drove it very far or up any real hills. And the last several days now it's been making this tinny rattling sound especially when I'm turning corners. There's also a squeal that sounds like it could be coming from a belt, but all the belts are brand new when I put the timing belt in first week of January. It's not overheating and the mechanic said it wasn't giving any codes. This is driving me f'ing crazy because the truck sounds like shit and keeps making all these noises. Especially in the dash board - before it used to just make that rattling dash board sound on cold mornings when I first started it up, now it does it damned near constantly, especially when accelerating and/or up hill. I had read it has something to do with the passenger side air bag and all tacos of that year range have it, but I'm not convinced of that anymore. I'm wondering if there's an air leak somewhere but I can't find any bad hoses. I replaced one hose back in jan but had to use a joiner piece on it because I couldn't find one long enough so it was two shorter ones spliced together at the center.

And another exciting new issue is that if I don't let the clutch out real real slow and gentle in first gear then I get this loud bang/pop sound that I can feel hit under the floor board. That's just started this week.

My brother suggested it might be a coil pack that's going bad but isn't throwing codes yet. So how do I know which one? He also suggested taking it directly to toyota for them to diagnose but I can't afford toyota's services.

Oh - and yes it was a timing belt kit with new tensioner, water pump, etc., I got off rock auto in Charlotte. I got the belt over the teeth where it needed to be then pressed that small center pully into place and bolted it down. Not technically the way it's supposed to be done but apparently it worked since I've gone about 1-2K miles since then and the mechanic said timing is fine.

 

You banging sound when you let the clutch out sounds like a trans mount. Does the shifter jump around a lot when it makes this noise? How did coil boots look when changed sparkplugs? (rubber piece under coil on spark plugs)

 

The power problem is probably a clogged cat, as for the trans I would guess trans mount