I have been having an issue with my 99 tacoma. It started a month ago when I would pull up to a stop light it would have a semi rough idle as if it were going to stall. After take off I would accelerate to bout 20mph and it would go away. No check engine light or anything. Now when I start it up it is fine until the engine warms up and it feels as if a cylinder is mis firing. I took it to a shop and the code is saying that compression is low. After compression test, results come back negative. Compression is fine. Changed the plugs, wires, coils, and even thermostat on the fuel regulator. I am not a mechanic and have no false illusions of thinking I know what I am talking about. The guy I took it to could not figure it out and the nearest toyota dealer is an hour away, or I would have taken it there. Any suggestions would be greatly appreciated.

 

A hole in a vacuum hose? A hose slipped off a nipple? Are you loosing coolant slowly? A slow loss could be coolant seeping into a cylinder causing the misfire.

How did the plugs look when you pulled them.

Thermostat on the fuel regulator?? Please clarify..... The only theremostat I'm aware of is in the cooling system.

 

Check vacuum hoses and block off nipples. A vehicle of this age most likely has some rubber parts starting to dry out and fail.

 

@rworegon- the plugs were black, the "thermostat" is actually a fuel regulator i believe. The block is pretty new only 60-70k. Its been replaced. @Duexrous- now that you mention it, it does feel more like a vacum leak. Thanks guys much appreciated!