carzan wrote:
Jensenman wrote:
Combination of carzan and iceracer's diag. Stick a vacuum gauge on it and fire it up and let it idle, if the vacuum starts good (around 17 inches or up) and drops back as the engine idles the exhaust is plugged (catalyst). If the vacuum starts off crappy (12 inches or so) and gets no better I'd look at the cam timing.
I would've given more thought to the cat if he said it came off the line with at or near-normal power, but felt weak as the revs/load went up. He says it gets power above 2000rpm. Doesn't fit my experience with a plugged cat.
A mostly (but not fully) plugged cat will do this but only under load. At idle the demands of the engine to get burnt gases out isn't as important. Since the partially plugged exhaust will only hinder flow at higher velocities, the idle vacuum (dependent on how much can be shoved out as well as pulled in) will start off good then drop. The engine may or may not idle well but you really got to get on it to get any power. In severe cases, there will be a loud 'hiss' on acceleration as the exhaust gases try to get out any way they can. Otherwise, there may not be a lot of indication that there's a problem other than power loss and MIL (generally a P0420 catalyst efficiency code). No mention of MIL in the OP's post but that is not really surprising, if someone cleared it and the PCM hasn't seen it enough times it may not light the MIL.
The missing T/C bolts tell me somebody had the bad timing/jumped belt idea already but that didn't fix the problem unless the timing marks were improperly aligned during checking/assembly (don't laugh, it happened to me on a 1.8 Subaru) so I lean toward partially plugged exhaust. That would scare me worse than a bad cat, as in why would the engine have jumped time in the first place? Possible answers (none good): momentary camshaft seizure (lubrication related), reassembly of an interference motor with partially tweaked valves, all kinds of stuff.
If it has less than 80K miles the 8/80 Fed emissions warranty would cover a bad cat. The OP did not mention mileage so I'm going to SWAG (Scientific Wild Assed Guess) that it's over 80K miles.
Loooonnggg shot: improperly adjusted valves (too tight) but I kinda doubt it. IIRC the 'Zook engines have HLA's (hydraulic lash adjusters) so I don't think human stupidity in that department is to blame. Although I have learned over the years NEVER to rule out stupidity as a proximate cause. 
