'02 Tacoma stumbles on acceleration.

I've recently replaced the engine on my '02 Taco, 2.7L, 4cyl, auto, standard cab and I'm running into some trouble. Every time I start it up it idles somewhat rough and when I take off down the road it runs fine for a minute or two, then it starts to stumble.

So far I've:
- Replaced oil pressure switch
- Replaced both O2 sensors
- Cleaned out MAS
- Replaced all plugs

These were just things I did after the swap. Any help would be greatly appreciated!

 

With the engine idling tap the MAF lightly with the handle of a screwdriver; if the idle fluctuates the MAF is bad. Make sure the EGR is working correctly and you have no vacuum leaks. In fact I'd start replacing the vacuum lines. I think the Coolant Temp Switch can be a problem, too.

 

I've already replaced the coolant temp switch, I forgot to mention that.

The EGR was my next step. I'll try out the tapping trick with the MAS tonight and taking a look at the EGR as well, maybe it's stuck. Thank you for the tip!

 

You could also just unplug the maf then start it and see if it idles better or worse. It will run in limp mode but you should be able to tell the difference. Also did you replace the plug wires with the spark plugs? If the plug wire isn't fully seated on the spark plug then you will stumble when you start driving too, check to see if they are nice and tight. I had a stumble and replaced my plugs and wires as well as the cap and rotor. Not sure if you have that or just coil packs.

 

I will double check the wires, I didn't replace any of them so who knows?

 

What is the source of your replacement motor?
Was the donor vehicle from the same year? Same tranny?

 

^^ Ya, I wasn't gonna say nothin'. That is a big ? and why.

 

Sounds like a vacuum leak to me based upon the history of the vehicle.

 

The new motor was a rebuilt from a shop. Same size as the original. As far as the stumbling goes, turns out it was a loose ground. Once I tightened it down it stopped immediately

 

Glad it was an easy fix. Thanx for sharing with us.