Surging/Hunting/Bucking

plcfcng

plcfcng

Member
I have been working on a 2001 Sport 2wd with what I can best describe as a Surging problem at about 1800 to 2800 RPM. I happens under moderate acceleration best felt when going up a grade. The engine is 10,000 miles off a fresh rebuild and has been running great until this point. At idle the engine runs smooth outside of the RPM listed there is no miss it has good acceleration. I have swapped the A/F sensor, MAF sensor and Throttle Body. Air cleaner spark plugs and wires are all new condition all quality parts. The 4runner was fine I left it for 4days upon my return I noticed the Surge. I find no rodent damage in the engine compartment or at the Evap system. Any Ideas would be helpful. I have been looking at previous threads and have nothing that will help me resolve the issue. :bluejump:
 
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Check for any CEL codes or pending ones (using an odb2 reader)?

Fuel filter?

Do you periodically run any fuel system cleaner?

Let us know. :cowboy:
 
This sounds electric or computer related to me. A poor ground or battery terminal connection could do this at certain rpms. A failing battery can also cause strange issues. Another thought was a vacuum leak of some kind. Any cracked hoses or connections?
 
No vacuum leaks, pcv valve new I can do a voltage drop test but I cleaned terminals and made sure ground was solid when I installed the engine as far tps goes I switched it with the one on my wires 2001 still had ht problem.
:pop2:
 
I'd say a fuel pressure test would be a prudent check at this point.

How new are the plugs and wires? Is it possible one or two of the plugs accidentally got their gap changed during install or are possibly going bad. Having a spare coil or coil set might be a good thing to eliminate them.

I've had vehicles run fine unless they were under load. The issue was some kind of resistance with spark. Usually a plug, wire, or coil pack.

Just trying to eliminate possibilities. These kind of issues can be a bear to track down much like intermittent electrical problems. The worst of the worst to find but usually easy to fix once found.
 
Well after a few weeks of trying to figure this one out I let my friend who is a master tech have it. After a couple of hours he figured out I had a partly clogged CAT. I had considered this was the problem but it would rev out clean in neutral so I thought my CAT's were good. I should have put my vacuum gauge on it so off to the muffler shop it went 675.00 later she runs great again.:usa:
 
Thanks for updating with your Fix - many don't do that.

So how many miles do you suppose the cat had on it? Just wondering cuz mine is still holding out at 320K....

Luck and enjoy the Runner. :cowboy:
 
How much oil does it use between oil changes, synth or dino oil, and at what mileage do you change it. Also does this vehicle see mostly city, highway, or about 50/50?

Dang cats are expensive!
 
I just rebuilt the engine a year ago and it uses no oil. As far a the age of the cat's build dates on the cat 7/16 for both so you could do the math it may have had about 30,000 about 10,000 but on by me. What may have shortened the CAT life was a blown head gasket it also looked like they used a head gasket sealer. The sealer may have coated the CAT's shortening there life. It has two new MAGNAflow's on them now. I have seen this condition pop up as I did research on how to correct it with no common answer so I hope this can help the next person with this condition. Again if I had done a VAC gauge test I would saved myself alot of head ache. :mullet:
 
plcfcng said:
I just rebuilt the engine a year ago and it uses no oil. As far a the age of the cat's build dates on the cat 7/16 for both so you could do the math it may have had about 30,000 about 10,000 but on by me. What may have shortened the CAT life was a blown head gasket it also looked like they used a head gasket sealer. The sealer may have coated the CAT's shortening there life. It has two new MAGNAflow's on them now. I have seen this condition pop up as I did research on how to correct it with no common answer so I hope this can help the next person with this condition. Again if I had done a VAC gauge test I would saved myself alot of head ache. :mullet:
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Cant you clean the cat out with cataclean??

Lots of folks had success with getting the cats to function properly again. However, maybe it's too carboned up. I look into a way to clean them before replacing. Way too new to be bad. ;)



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I have seen videos about cleaning them I just didn't want to take the time to do it. While 675.00 is a bit of change I feel not making a car payment I could spring for the CAT's. :dancin:
 
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