Hi all,

I've reviewed all the similar threads regarding vibration present during idle, and have found no solutions. I think my sig is still present, but if not, I have a 91 LX five speed, about 203k on it. Runs great, but has developed a vibration at idle, after warmup. The idle speed is fine, about 750 rpm. At the first hint of acceleration the vibration disappears. In the last 18 months, I have done a great deal of maintenance. I tracked down a fuel delivery issue and examined most of the common culprits. The car has ngk platinum plugs, good quality wires, new cap and rotor, coil (when it failed). For the fuel delivery issue, I replaced a rusty gas tank and the original pump and filter. Valve lash was recently adjusted, and I had even replaced the lower plug tube seals. The plug wells are dry as a bone. The car has run beautifully, and really still does. It seems to return about 28-30 mpg on my work commute. I tested the EGR function, and it stalls dead as soon as I draw a vacuum on the EGR valve. I did try unplugging the IAC valve, and the car would not idle. I think I remember hearing that this was not normal. I don't see how the IAC could cause this vibration (since the idle speed is correct) and I sure don't want to buy an IAC I don't need! Any suggestions from the peanut gallery? Oh yeah, the motor mounts seem fine too, solid with no cracking or sag.

 

If the BASE idle is off, the IACV can correct, but then it's not in the right part of it's control range. I'd expect that to cause surging idle, instead of vibration. But anyway...

Clean throttle body.
Throttle cable must not hold throttle open. Has to go slack.
Mechanical throttle stop screw only just prevents it from sticking shut.
Air-bypass idle screw is recessed in a hole above TB bore...
Engine all warmed up, NO electrical or AC loads are running.

When you unplug the IACV, nurse it with the throttle to keep it going.
Adjust air-bypass idle screw for about 550 rpm.
Turn off & cool down.
Reset ECU by pullling (-) battery cable if you know your stereo security code.
Start engine without touching the gas pedal.
Let it warm up completely without touching the gas pedal.
DONE.

 

Well, now I'm getting a CEL about 5 minutes after I begin driving. It's a code 12, which I understand translates to EGR lift sensor. The car stalls when I activate the EGR valve, so I don't think the passages are clogged. I plan to get the service cap kit and clean them anyway. I think I'm going to replace the EGR valve with sensor, since it's so old. (It is the original.) As near I can tell the vacuum solenoid is working; there is no vacuum at cold start, and the light comes on when EGR operation should commence - warm engine setted into a cruise conditon. Is there anything else I should check before condeming the EGR valve?

 

Code 12 means the EGR system is not responding as expected. It could mean the manifold pressure is not changing when EGR is opened, EGR valve is not lifting as expected, vacuum to EGR is not present, etc. You need to go through the diagnostics in a Honda Shop Manual to isolate the fault.

The one thing about EGR system it probably doesn't mean is the EGR ports are blocked. I've never got a EGR fault w/ a 90EX or 94EX w/ completely blocked EGR ports.

good luck