[Hippiefeet]

I was brought a '94 Previa w/ a 2.4L, no super charger, that overheated blowing the head gasket. The head received a valve job and was reinstalled w/ new plugs, wires, efi temp sensor, and thermostat. All timing marks are lined up. The rotor in the distributer seems a hair off from #1 wire at TDC. But there seems no adjustment that can be made for that.
The engine dies at idle when cold and runs better when warm. Road tests seem OK, plenty of power and no vibrations. After the engine reaches full operating temperature the engine light comes on showing a 52 code (knock sensor)...
I am stuck from there... anyone have any suggestions?
Thanks

[kitch428]

Here's all the repair manual says about knock sensor. DTC 52

With engine speed between 1,600 rpm and
5,200 rpm signal from knock sensor is not input
To ECM for 2 crank revolution. (KNK)

And to check...

• Open or short in knock sensor
Circuit
• Knock sensor
(looseness, etc. )
• ECM

Now keep in mind the wire for the sensor is shielded, like coax cable, so it don't run interference.
Once this wire is disturbed, it can become brittle on older cars and may need a new wire. I used to just go to radio Shack and pick up a spool of small shielded cable and run a new wire to the ECM.
As I said in a PM, this puppy is buried under the intake, and that's under the Van! Yuck!
Well, the diagnostics isn't bad, but the repair is a bear.
I'd be more concerned with why it still runs so crappy cold and stalls. Look deeply into the throttle body for that. Unplug the IAC and see if it runs any better when starting up cold.
That's under the drivers seat engine cover. Good luck.

Oh, and when you drive it again, first pull the cover off above the radio and look into the fuse panel for the EFI fuse. (middle row, far right) Pull that fuse for a minute and it will clear out all the codes for the next trip cycle.

[Hippiefeet]

I replaced the knock sensor and the code went away. It turned out the sensor melted. I am guessing from the engine overheating.
But the engine still will not start with out holding the accelerator and will not idle when cold. I am receiving no engine light or code. If I hold the accelerator lightly, it seems fine.
I have found it could be an EGR or Idle control valve problem. Plus a hundred other things I'm sure could have been affected by the overheating.

[Hippiefeet]

I have also replaced the fuel filter, distributor cap, and rotor. I could not believe it had the original fuel filter after 160,000 miles. My jaw dropped.

[kitch428]

I would serously think about removing the throttle body and cleaning everything in sight. Esp the EGR passages. The IAC really should be replaced. Too many miles to try and Band Aid repair it.
After that, I bet it will purr like a kitten. Congrats on the knock sensor. Good job!

[Hippiefeet]

Ok, I will give it a go. Could you specify where the IAC is?
And thank you, the sensor was not much of a job, considering I have the tools.

[kitch428]

I've attached a page from the repair manual. This should explain.

IAC.pdf

[Hippiefeet]

I removed and cleaned the throttle body... was extremely filthy and I think a couple vacuum lines were clogged with engine gunk along with most of the throttle body itself. As dirty as it was, I decided to put on hold replacing the $IAC$. I found the IAC attached to the underside of it. I tested it by plugging the IAC in still attached to the throttle body and felt for a very faint clicking and vibration, it seemed good so I did not replace it. After I had the throttle plate cleaned to a shine (chemtool carb cleaner works wonders) and vacuum lines cleared out, I reinstalled it. After I turned the key the van started without hesitation and ran smoother than it had before.
Thanks Kitch428! You saved me from a huge headache.

[kitch428]

Good deal!