My Montero has a small vacuum leak that I have not been able to find. I forgot the code, but I have changed gas cap and other things. Anyways, it's been like that for over a year without any performance issues, except for the Svc Engine Soon Light on most of the time. If I disconnect the battery or reset it with a scanner the light will stay off for 3-4 days before it comes on again with the same code.

Lately, during normal driving once every 4-5 days, during acceleration, the engine will suddenly loose power and after 1-2 seconds it will continue just fine. It will not stall, nor shut off, nor sputter, nor ping, nor do any abnormal sounds, nor loose power for a prolonged time, it will just momentarily loose power and then continue normally.

Any ideas, suggestions, or diagnose?

 

Sounds like your vacuum leak got bigger and engine PCM is, at times, unable to compensate for it. Disconnecting the battery to turn off check engine light is useless. You are not fixing the problem and you are not fooling the PCM. After couple of drive cycles it re-learns the fuel trims, figures out that they are out of whack and turns the CEL back on. You need to find your vacuum leak and fix it. You can have a technician put a smoke machine on it and you'll be done in 15 min. You can try try doing it your self too. One way to do it is to get a can (or two) of starter fluid and with the engine running at idle, spray around at different parts of the manifold, vacuum hoses, etc. (everywhere after MAF). When you find the vacuum leak, the engine will momentarily increase RPM. You can repeat it again in the same spot and will be able to confirm where it is. After that its just a matter of replacing a bad hose, gasket, etc.

 

Hunter, thanks for your advise, will try the starting fluid trick; pretty much sure most mechanics around my area don't have a smoke machine.

BTW, I know I am not fooling the PCM, just mentioned it as an example to show how long it takes to detect the problem again.