QuestionGood day. One month ago I purchased a 1996 Mitsubishi eclipse rs with 130,000. I have given it a tune up, replaced the rear seal, and have had it checked at various mechanics. It will idle low, rough and steady, almost like its throbbing. But the car will run fine when in motion. The car also runs fine in idle when the A/C is engaged. Here is a list of things I ve done to the car:
replaced rear seal
changed oil/oil filter
replaced air filter
replaced fuel filter
replaced spark plugs
replaced spark plug wires
replaced catalytic convertor
replaced muffler
replaced all belts (minus the timing belt)
replaced all hoses
replaced EGR valve
cleaned EGR piping
cleaned throttle body
added engine cleaner
added fuel line/injector cleaner
ran compression tests/no problems
Whats left to do....
change battery/low, but not enough to show serious signs of electrical failure
replaced o2 sensors/see below
lights, brakes,..other things not related to the engine.
I have had it electronically scanned at 3 shops.
The first shop said the scan showed it needed a new EGR valve and o2 sensors.
They also recommended that my valves be replaced.
The second shop said the scan showed it needed a new EGR valve, and catalytic convertor
I replaced the EGR valve and catalytic convertor
Same symptoms
The third shop showed the map sensor voltage reading was high and that there was EGR errors.
Before I shell out money on what might be more unnecessary repairs, what could possibly be causing this rough steady throbbing idle???
Louis
AnswerLouis,
Rough idle can be caused by a faulty IAC (idle air controller) or even a clogged PCV valve. A new PCV valve only costs a few bucks and is real easy to replace. Try that first. If you have a service manual, it will walk you through the procedure to test the IAC. There is a idle setting screw located on top of the throttle body. The little o-ring may be worn and is leaking air. I would attempt to check and replace these smaller items before spending more money on large ticket items.
Good luck!
