Hi all, I bought a '94 4Runner 3.0L recently and its been running extremely rough. Heres the symptoms and what I've checked so far:

- CEL on, code 25/ lean. Takes about 5-10 miles to set this code after reset.
- idles very rough, slow acceleration and very rough to about 3k RPM, then smooths out. Power intermittently flucuates above 3k RPM.

- Plugs gapped and good, wires good, cap and rotor good. o2 sensor good. Coil tests good. Timing set to spec. Vacuum good and steady. cleaned the vacuum ports on the throttle body, checked all vacuum lines.

- #2 spark plug was slightly sooty and smelled a little of gas.

--> I unplugged the TPS with the engine running and it smoothed out perfectly, idled smooth. HERES THE WIERD THING- Leaving the the TPS unplugged, I reset the ECU and now it runs rough- the exact same as it used to WITH the TPS plugged in.

Any ideas?

 

is the tps properly adjusted?

 

I havent checked it yet, but the engine runs badly after resetting the ecu and leaving the tps unplugged. If I dont reset the ecu, and leave the tps unplugged, it runs smooth.

 

A TPS reset/replace and fuel filter change would be where I'd start.

 

i have seen those same symptoms from a faulty tps. I would replace it and adjust it and i bet it will purr like a kitten.

 

so it sounds like the tps even though it runs very rough with the tps unplugged? (after ecu reset)

 

try unpluging the afm

 

I'll sum it up:

While running/ idling:

Only if the CEL is on (with code 25 lean) and the tps is unplugged, the engine idles smooth. Still misses under load under 3000 RPM.

If the CEL is NOT on and the tps is unplugged, there is no change between unplugged and plugged in.

 

So, with the cel on, it runs smooth?

That might be because the computer is retarding your timing. I remember when I had a code 52, it would run real smooth and all, it was just powerless...couldn't get up hills good, etc.

When that code is thrown, the computer tries to compensate for whatever is missing...that might be what you're getting.

I'd just change the tps. That's what it has to be. Maybe your throttlebody is clogged up too...I know mine had soot from hell all inside when I took it off to check the tps.

 

ok, I'll look into changing the tps and cleaning the tb. I still don't see why if the tps is at fault there is no change in the way the engine runs when the tps is unplugged with the cel off.

Also, even though it has good vacuum, could there be a slight vacuum leak cause the extreme roughness?

 

hey is there a slight chance your knock sensor is acting up

 

I suppose theres that chance.. I havent check it yet though. Wouldnt the ecu set a code for it?