I have a miss or something in my 93 pick up. I had just did a engine swap, run fine with only a slight hesitation at the begining of the rpm range, as the rpms gotr higher it picked up. Now it seems to be getting worse.

Here is what I have as miss or hesitation. It seems to come and go, not consistant at all. While driving it will be fine and then out of the blue it will start, then it will go away, then come back. It seems to have started after it has been a little colder out, might be a coincidence.

It does it any speed other than a the very begining of the throttle and full throttle. If I give it full throttle it accerates great, if I leave off full throttle the slightest bit it misses or hesitates and accutally slows down. Sometimes when I come to a stop it idles really rough like it's missing or something.

Timing is good and it has a brand new timing set installed by a ace mechanic, before I installed the engine. My average gas milage has been around 16 - 17 in town with a 24 mpg on a 240 mile highway trip ( that was before this started).

My check engine light was on from the start after I installed the ingine. I had installed the jumper wire to check for engine codes and got a 21 (o2 sensor). I did not get any other codes.

Would a bad o2 sensor be causing this problem? The only thing I did not put new on the engine was cap & rotor and plug wires because they looked fairly new and in good shape.

Any ideas or info would be helpful, I'm hoping it's something simple.

 

Not the O2,check throttle position or mass air flow.Or vac leak.Stuck EGR.Take the cap off and look at the terminals,check the date on the wires.Pull the plugs and inspect.Cat converter OK?

 

I have no vacume leaks. Not sure about the CAT.

Out of all the things you mentioned, which one of these would cause my miss or hesitation to come and go? Thanks

 

I had a bad plug wire that would come and go. I just happened to open the hood when it decided to arc from the wire to the engine and I heard it snap. Looked a little harder and finally saw the spark jump across to the engine a few times. Replaced the plug wires and all was well.

 

I have been wrestling with the exact same thing for a while now. I have checked, double checked and triple checked everything I could. After getting copies of the pages out of the factory service manual and doing a bunch of different tests, I think I finally narrowed it down to the TPS.

I was able to adjust the TPS so the resistance readings were whithin the specified ranges, but I would drive it a day or less and the problem would return. It seems the TPS won't hold the adjustments internally.

I still haven't replaced it to ABSOLUTELY confirm this but it sure seems to be the culpret. I just narrowed this down last week. At $140+ for the part and Christmas only two days away, I simply unplugged the TPS. It seems to run fine except it idles higher than before and it doesn't drop down when you jump the leads in the Diagnostic connector. I figured I will replace it later after I recover from Christmas.

It was doing EXACTLY what you describe and kept getting worse until finally here I am.

I hope this helps. Let me know if you want way too much detail and I will cut and paste my trials and tribulations from another forum.

Good luck.

 

Keep me updated on your progress.

If you could, post the link to the other thread you mentioned , I will read through it. thanks

 

Here you go.

http://www.toyotanation.com/forum/t159076.html

If you could, unplug your TPS and see if your problem goes away like mine did. I'm just curious to see if yours does the same thing. The only real negative effeect I've seen is that you can draw a code out of the ECM with it unplugged. No CEL though.

I won't be doing anything for at least a few weeks because I'm flat broke right now. So for now it's staying unplugged.

That same site has free FSMs at the top of the section too.

Good luck.

 

After reading your thread, I see that your problem seems to stay once it starts. Mine comes and goes anytime it wants.

I read the one post that suggested a fuel delivery or pressure problem. It had me thinking, even though I had replaced the fuel filter before I started the truck for the first time. This truck had sit for over two years, because the previous owner didn't bother fixing the blown engine. I found out that my fuel tank was dirty and gunked up and I had run it a little as I was testing out the engine. The fuel pump screen was gummed up and wasn't allowing enough fuel through to run properly. The fuel pump was recently replace before the engine took a dump.

After removing the tank the fuel pump sceeen was gunked up and the tank was full of crap. I ended up just spraying off the fuel pump screen with carb cleaner to remove the gum and did a whole fuel tank cleaning.

Do you think some junk got up into the fuel filter and possibly is restricking the fuel at times. I kind of ruled this out because of it running fine at times and especially at full throttle when you need the most fuel.

 

Mine used to do it intermittantly just like yours. It became more and more "mittant" and less and less "inter" until it finally did it all the time.

Unplugging the TPS is the only thing that has fixed it so far. Thats why I never went into the tank.

 

This mornining I used the truck to go to a friends house and it acted up on the way there. Before I left (15 min later) I disconected the tps wire and the idle jumped up. The idle seems to be better than before because I had a very low idle. It ran fine on the way home (10 min drive).

I thought I would go take another drive to fuel up and see if it was still ok.

Well it seems like the problem is gone and I don't this the truck has run that good since I have been running (around 1000 miles).

I have read that the tps can be adjusted. Do you think that is what needs done or do I need to replace it? I have another off the old motor. I would have to take it to someone that knows what thet are doing with tps, since it seems pretty technical.

If you or anyone else have any other thoughts or info, it would be greatly appreciated.

Thanks