Undiagnosable Miss-- Help!! Number 2

My 95 4cyl. 2.7L Tacoma 4x4 188,000mi has a problem that no one can seem to find. When first start the truck the engine runs smooth, then in about two miles it begins to slightly miss approx. every 8 10 seconds and as I continue to drive the problem becomes worse- it will run smooth up to 1800 rpm, then it starts missing, but otherwise in between misses it runs okay. I have replaced the cap, rotor,coil, condenser, and wires two times, and the problem still exists. Brought the truck to a Toyota dealer and they performed a compression test, computer diagnostic test, and fuel pressure check-- all were systems and results showed no abnormalities- the machanic suggested another set of plug wires, which I did replace and even replaced the new NGK plus with Bosch- the plugs I removed and they looked really clean, so its not running rich and even replaced the condenser again, but the problem still persists!! I did just notice that fuel injector 1 and four appear to loose as I can rotate them back and forth. As a test I unplugged each injector one at time and the engine ran with the same consistant roughness each time , but the miss still persisted, also the check engine light only comes on during start up then shuts off. Any suggestions would be greatly appreciated.

 

Welcome to the Forum, Josh, I am sorry about your problem. You have deligent about working on the ignition side of the complaint, but your problem is more than likely Fuel related. Access to factory information is limited, but I have accesed some info from a model one year earlier than yours. This info may lead you down another path that could be part of your problem. I know they performed a fuel pressure test on your Taco, but did they do it after it was warm and subject to miss, or did they test it cold and just run the test and stop.
You may something failing after it is warm, it may test good when cold, but after warming up to normal temperature, it may show some signs of breaking down. I would look at your fuel pressure regulator and the indiviual injectors as possible sources of your problem. Inspect all your engine wiring for possible shorts and bad or loose connectors on the wiring. There are procedures for testing the injectors there and I am sure the pressure regulator also.
You also may want to look at your engine vacuum with a good test guage and see if this changes from the time the engine is cold till it warms up. Something may be failing along in this area also. This should give you some steps to see if any of this helps. If not works out from this line of inquiry, then we will do more research and see what we can find. Good Luck.

 

Sounds like it might be a vacuum leak. But I am no professional

 

First off, welcome.

Here is a link to the factory service manual. I'd download it for sure as you will find it invaluable in keeping your truck maintenanced and repaired.
Some random thoughts that may help.

First thought was a coil issue, but you say you've replaced that.

Then thought comes to something related to the engine warming up and changing. Of course heat can change how electrics work. Reason I thought of coil as they often heat up and then start malfunctioning, but as I said, you said you replaced that.

Also wondered about fuel. At initial start you would be running richer until warm. Wondered about an injector issue. Manual says injectors at 68 degrees should ohm out at between 12 and 16 ohms if I read it right. Maybe give them a test to see.

Any issues with injector O rings I wonder....

Have you tried to pull the codes again to see if there is anything. If you don't have the tool you can get it done at AutoZone or O'Reillys.

Keep everyone updated on progress. Lots of good people on here willing to help.

Cheers