6G Celicas Forums

Long story short, my 5s has a pretty rough idle when not in park. Got the car with no grommet in the pcv valve. After replacing the pcv valve and grommet, the car had a significant loss of power, and the idle was rough and low. So low that it would bounce around and eventually stall if I came to a full stop for too long. Reinstalling the original PCV/grommetless setup didnt help, so the car was towed to the mechanic, where they managed to get it to drive a little better, but couldnt solve the problem entirely. Ran some seafoam through it, and I got a lot more power out of the car, but the car would still idle rough and eventually stall(although it was significantly better than previously.) Last thing that I did was adjust the idle speed screw, and that seems to have acted as a bandaid for this problem, but I've read that this solution may not be permanent. No stalls since this, but the idle still gets rough. Heres a little list of whats going on.

The Bad
-CEL, showing p300-304(random/all misfire), P171(System too lean)
-Idle bounces ~700-400 RPM
-Loss of power
-When battery is disconnected, ECU seems to have a steep learning curve if you will, as it takes several days of driving before the car starts to drive somewhat normally again. Could be due to the lean fuel/air
-While at the mechanic, we ran some fog through the intake and saw that the EGR was leaking pretty bad.

The Good-ish
-Compression tests done at shop, cylinders okay.
-Seems to idle better when cold.
-The rough idle can be "fixed" about 70% of the time by turning on the AC. This makes me think the problem is air/vacuum related, and not fuel related.
-The rough idle also tends to go away once I get the car on the highway, or if I get it around the 4-5k rpm mark. Like the AC, this doesnt always work.

At this point I have ordered a new EGR and vacuum modulator, and am waiting on their arrival. If that doesnt solve the problem, I was thinking about replacing the injectors and fuel pump, as the seafoam did seem to help a little and the ones in my car are older and could use replacement anyway. Besides that I'm not sure how to tackle this issue. Any help would be appreciated.

First I'd get a scanner, or take it to an Auto Zone or somewhere they can read the CEL codes for you.
That will give you an idea of where to start.

do a compression test. im willing to bet all your valves are tight causing the misfire.

Could be sucking air somewhere. Hopefully the EGR will fix it.

Right now I'm replacing all the vacuum lines on my car. Seems like everything made of rubber on my engine is cracking and falling apart.

Just had the P0304 problem - engine misfire

Pull out your spark plug wires. If there's oil, your valve cover and the seals are leaking oil into the sparkplug causing a misfire.

Oil can leak into the distributor too.

If your idling is 400 and hardly 700rpm ,the revs goes up slowly than before? Cause I had this problem and the 2 injectors of 4 didn't work..I don't know about 5s.I have 3sgte