Willisbullard

Hello,

I just bought a 95 4runner, 160k miles, new o2 sensor, new timing belt, new water pump, new air filter and tuneup. Check engine light is on, and ran the code today, and it came up as 2552, which is labeled Throttle/ Fuel Inhibit circuit.

Is that just a switch or something like that? I haven't been able to find anything online about that code for a Toyota, other than the definition.

Truck seems clean, just purchased from private party. Doesn't look obscenely clean or cleaned out just to hide leaks or issues. Bought it for cheap and thought it would have some issues to deal with (and it does have issues), just not sure where to go with this one, I am thinking it could be a plugged catalytic convertor, blown head gasket, but want some suggestions or other's experience with same code/ issues.

Symptoms are, slow/ no power at speed, usually up at 50 mph. It also gets the shakes sometimes at that speed and higher, when engine downshifts, often runs smooth. Sometimes it won't downshift and I have to turn overdrive off on long/ large hills, and when really bad, have to hit the ect to keep rpms up and not start feel like I am rolling backwards.

Also, no smoke out of exhaust, and I can't smell anything, but my sense of smell is no good anyway. No noticeable leaks either. Anything else I should look for? Any suggestions?

Much appreciated.

scope103

Is this an OBD II vehicle? If it is, I can't find 2552 (should be P2552, for power train) either. Not even a definition.

But if it is an OBD I (like the majority of '95s I've heard of), there is no such code. Are you sure it isn't 25 (A/F lean malfunction) AND 52 (knock sensor signal missing)?

Willisbullard

You are right! I did it and read it wrong.

Now, what should I target with those 2 codes? Knock sensor looks pricey and a buddy of mine said, "you don't need a knock sensor to tell you it's running rough". Is that a must fix? And then the a/f lean, where do I start?

scope103

You can start by not listening to your "buddy."

First the easier stuff: there are lots of causes of 25 (that's why you look at the manual), but the first on my list is a vacuum leak. Air is added after it's measured in the VAF, and leans out the mixture farther than the ECU can compensate by looking at the O2 sensor.

The knock sensor itself is probably not the problem, instead the pigtail from the sensor to the outside of the intake manifold is almost certainly shot. (Search here and you may even find the part number.) The bad news is that you have to remove the intake manifold to get to it, and even once you're in there isn't any good way to test the sensor.

The knock sensor is often misunderstood; start with "code 52 has nothing to do with the engine knocking." The ECU sets the ignition timing by slowly advancing the timing until it senses knocking, then retarding it a bit. If it loses touch with the sensor (like the pigtail crapping out), it can't tell if the timing is too far advanced (which will blow a hole in a piston), so it dramatically retards the timing to save the engine. That's why it runs so badly (notably, no power) when you have code 52.

Willisbullard

Great, thanks. I'll dig in and let you know how it turns out. Starting with vacuum etc. Then get on the intake manifold and get to the knock sensor. Thank you!

Willisbullard

Thanks again for the help, one last question before I report back on progress (nothing done yet), but I am guessing I will make something worse if I drive with the knock sensor or the pigtail needing to be replaced? I can carpool to work, but may need to drive it 60-80 miles before the weekend when I can get cracking on fixing. If I should leave it parked, I'll make that happen. Thanks again.