I've got an '89 IROC with LB9 and 5 speed. Recently I've had a low rpm (below 1500) engine vibration with an intermittant rough idle.

I've checked for vacuum leaks and loose connections and found none.

My TPS is set at .54V and my initial timing is at 12*.

A visual inspection of ignition wires shows no defects.

By the way...the car has 9,000 original miles and the ignition wires are original equipment.

Any suggestions?

 

You have an 89 IROC with 9000 miles on it and it's still got the original ignition wires on it. :hail: :hail:

Spark plug wires do brake down inside and then resistance goes up.
Might be a good time to do a complete tune up, new cap, rotor, wires and plugs.

Does it still have the original air in the tires?

 

I'm sure that there still is some 1989 air in those tires!

Anyone know how to tell if ignition wires have gone bad...even if they still look new?

 

This is why I believe my problem IS NOT ignition related.

When I give it throttle the engine pulls and revs cleanly and crisply.

Only at low RPM does it run rough. In fact , below 1500 rpm, if I don't depress the clutch pedal when decelerating, the engine begins to "buck".

I was convinced it was a vacuum leak, but I've visually inspected it several times and used half a can of carb cleaner on all the vacuum lines I can see.

I hope it's not the EGR...it looks like a bear to replace.

HELP!....I need ideas!

 

Ok, I searched for vacume leaks again today but again couldn't find any.

I also inspected the TB and IAC passage for dirt. They were clean, but I sprayed carb cleaner in there anyway.

When I started it up today, It idled smoothly at about 1000 rpm for about 30 sec. and then roughened up again when it "settled"at 750-700rpm.

By the way...there are NO trouble codes.

Any ideas?