I have a 1998 Honda civic, i've been having problems with my idle and lack of power. After i rev it up, the rpms will drop a little lower than 500. and start shaking as if it's about to stall out. Then it just rises back up to normal.

I took my car to a mechanic and told him it was lacking power, He said that everything mechanically was good, clutch was good, compression was good, no vaccum leaks. All he found was exhaust leaks, which i fixed. I'm still lacking ridiculous amount of power and i'm all out of ideas.

When i get on the gas, it's sluggish at first 'cause of the low idle, then it speeds up a little bit. after 30 - 40 the power loss is most noticeable. The engine gets louder, but it does not accelerate.

anyone have a clue as to what it could be?

 

Lotsa vagueness in this post.
Exactly which Civic are we talking about?
Any CELs?
When was the last full tuneup?
This happened after what?
Are you trying to floor it?
Is ignition and mechanical timing correct? Don't tell me that the mechanic didn't know. I'm asking you.
Are you sure you're lacking power? These cars didn't have power to begin with.

 

It's a b18b1 bottom end, not too sure on the top end, the person I bought it from said it was stock but I don't think they made a dohc stock in a civic. It Has lots of after market parts. But I know for a fact it lost a lot of power 'cause it actually used to be able to get up and go. The mechanic I brought my car too only works on Hondas and has worked on them most his life. Like I said, everything mechanically is good, he said it wasn't in need of a tune up, but I've replaced a few things and cleaned a few things but that didn't help. The power loss happened out of no where.

And yes. When I try to floor it, it gets loud but doesn't accellerate like it used too. I tried changing my fuel filter to see if it was clogged, didn't change. Maybe my injectors are clogged?

 

B16s came in Civics. Not B18s.
You said compression was good? What numbers are we talking about?
Is ignition and mechanical timing correct?
Any CELs?

You're only answering half the questions.

 

The bottom end is swapped...
Timing is good, No codes other than things that need to be bypassed.
I don't know a ridiculous amount about cars, other than what i've fixed and worked on so far. Which is why i'm on here, to ask for advice.

I bought this car back in december. Used to be fast, now it's not at all.

I cleaned the IACV, replaced fuel filter, spark plugs, fixed exhaust leaks, cleaned up the cap and rotor. tried switching to 92 and using octane boost, i've put so much time into trying to figure out what's up with it and i haven't been able to figure it out.