45shutr

Hey guys and gals, I am putting together an '87 4runner, I have installed and new motor, trans and transfer case, new manual hubs, along with various sending units and sensors. At first it ran great, I would say about 2 weeks, then one day I went to replace the O2 sensor and immediatly it wouldn't run right. It would misfire like crazy at idle after it warmed up. I got to the point where I felt there were too many variables going on at one time for me to be able to diagnos the underlying issues and correct the problem. Therefore I took it to a local shop to have the car gone through. After the shop was done with the car it ran good again, while at the shop they replaced the Idle Air Control Valve, cleaned the MAS, throttle body, checked the function of the EGR valve and adjusted the timing. Like I said the car ran great out of the shop, but now, about a week later the car in about 1 out of 3 starts will cough and sputter and refuse to start, I can finally get the car started by continualy cranking and pumping the throttle, other times the car will start with no problem. It seems to run ok on the road once started, but seems to be lacking a little bottom end power, the motor seems to come alive at 2700 RPM. I don't know if it is because the motor is new and needs to break in or what. The shop said that the computer was not advancing and was a little slow in doing its job. I am not sure how much the computer has to do with starting the vehicle or not, but I sure wish I knew how to test the computer to check for problems. Anyhow like I say, I am open to suggestions and would appreciate some guidance. Thanks in advance.

wyoming9

iTrader: (1)

First of all pumping the throttle does no good unless you have a carb which if the shop replaced the Idle Air Control valve you have a Fuel injected engine.

It also sounds like the shop was clueless as to the real problem.

Was this a rebuilt engine you did or a used engine??

Sounds almost like a vacuum leak where all new vacuum hoses installed or a hose on wrong.

It seems all related to the Oxygen sensor did you get a bad one?? did you break or pull something else loose at the time??

Have you tried a different one??

Although it should run enough to get you home safe with it disconnected

What was wrong with the Oxygen Sensor you changed ??

45shutr

That's the funny thing about pumping the throttle, despite the fact that it is a fuel injected motor, pumping the throttle is the only way to get it started when it is "acting up". I wonder if pumping the throttle has something to do with the TPS having some issue or problem? Oh well might as well check that while I am at it.

After the shop was done with the car it ran great, then a week later the problems started, so I am less inclined to think that they missed something and more inclined to think that maybe I just "got lucky" and now something else has gone kaput. Althought at this point I am not ruling anything out.

The motor is a reman'ed unit built by a credible engine builder and has thus far been running great as far as the engine internals are concerned.

As far as a vacuum leak, I have gone through and searched for leaks via the good ol' can of starting fluid trick and found nothing. Going back through and double checking the routing of the vacuum lines is a good idea and I will do that. Keep in mind though, the issue of hard starts and then the motor misfiring and shaking violently is only at start up. If in 1 out of 3 starts it decides to act like this, in about 10 seconds it will smooth out and run fine. The motor will surge a little bit after it smooths out, but I am sure that is do to the fact that the valves need to be adjusted following the break in of the motor.

In regards to the O2 sensor, we replaced the old one because it was probably the origonal one and after 20 years I thought it was probably just a good idea to replace it. I was thinking the same thing and though that maybe we pulled something loose when changing the O2 sensor and therefore went back and checked the leads to the O2 sensor to varify they were in good shape and still connected, and they were. I have not tried a different one but, I don't think that the O2 sensor would have this profound of an effect on the motor and only at idle, but I will do a resistance test on it anyhow just to make sure.

Thanks for your reply wyoming9, I will check these various items on the car and let you know what I found in a few days.

45shutr

Well, I went and checked the TPS today and the idle circut of the TPS does not check out. The throttle closed and wide open throttle circuts of the TPS did check out. Seeing how the issue at hand is one that occurs at start up, right at idle, it would appear that this could be the issue. I am going to go down and get a new TPS tommorow and give it a shot. I will write back with my findings.

myyota

A bad TPS can cause starting problems, so replace it and make sure its properly adjusted and see if that solves the problem.