Hello, I am not new to YotaTech (Ive been reading forums for tech help for about a year now), but this is my first post. A few weeks back, I changed my water pump, timing belt, and tensioners on my '88 Toyota Pickup 3.0L V6, and after finishing the job and starting her up, I noticed a rough idle and hesitation/stumbling under acceleration. I figured the issue must be timing related so I messed with the ignition timing and after it didn't solve anything, I read some forums and thought maybe my timing belt had skipped a tooth or I installed it incorrectly. Turns out, I had put it on right because all of the timing marks still lined up (ignition timing is also back to the recommended 10 degrees BTDC). After this, I figured out how to pull codes from the onboard diagnostic system and saw that I was getting a code 41 (TPS circuit short). I adjusted my TPS to spec using a chart I found online from the FSM and reset my cars ECU by disconnecting the battery overnight. This solved 80% of the stumble/rough idle, but it is still noticeable even though my ECU is no longer throwing any codes at all. Is there a way to test other parts of the TPS system/circuit before I buy a new sensor? I don't have much electrical knowledge or experience and I know the short could come from anywhere in the circuit, not necessarily just the sensor. If someone could explain, point me in the right direction, or let me know that my diagnosis is completely off, that would be great! Thanks!

 

Have you looked for a vacuum leak? Did you take the upper intake off? Check the hose from the PVC to the upper intake and make sure its plugged in right. Reading your description its the first thing that I think off.

Jake

 

Thanks for the response! I have looked for vacuum leaks by spraying brake clean on nearly all of their connecting points, but the engine never increased in rpm. I also double checked the PCV valve line, and it's still connected well. When I changed the timing belt I had to take part of the intake plenum off (just the throttle body side, I pivoted it up) so I could reach the bolts holding the #2 tensioner on (thats part of the reason I thought it might be a vacuum leak too). My best guess is that it is something air/fuel mixture related, and most likely electrical related, but I'll make sure to double check my vacuum lines again to make sure they aren't the culprit.

 

I double checked the vacuum lines this morning and again, none of them seem to be leaking. Is there a way to test the TPS wiring to and from the ECU? Also, if you have any other recommendations that would be great! Thanks for the help so far!

 

Short of getting a smoke machine to check all the vacuum hose integrity. If you short the service block to set the timing and the check engine light flashes then the TPS itself and wiring is probably fine. There is a way to check a TPS sensor on a bench but I have never done it. Should be Youtube videos. So if you short the diagnostic plug the timing goes to 10 degrees and holds steady? Un-short the diagnostic plug and it goes to 8 and holds steady?

Jake

 

Checked timing by shoring the T and E1 terminals, ignition timing checks out either way. A few nights ago I adjusted the TPS using a multimeter and a chart found in the FSM. I did end up checking the diagnostic and it is throwing a code 41 again…

 

A little update, took the truck for a drive and the engine surges every time I press the brake pedal, any ideas? At this point I am completely lost because to my knowledge, the engine and brakes are completely separate systems…

 

They are on different systems. But the engine is still responding to loads put on it. Like braking. I am out of ideas without standing in front of it. It still sounds vacuum related to me. But could also be a combination of things.

Jake

 

after you got done adjusting the TPS is the top set screw roughly in the center of the slot?
Actually, is the distributer adjusting bolt fairly centered, too?

 

Actually, the engine and brakes are related. The ECU has a program in it that will, when the RPMs are above a certain point, like about 1100, cut the injectors off, when the brakes are pressed. Once the RPMs are below the specified point, the injectors are allowed to function again.

Make certain the idle RPMs are below 1000. Preferably about 800. That may well stop the brake induced RPM surging.

Does that help at all?
Pat☺

 

Yes, adjusting the idle solved the surging when the brake is applied (thanks, I never would have guessed), however, I'm still having TPS related issues. Does anyone know of a diagnostic chart or something to help me determine whether the short is coming from the wiring or the TPS itself?