i am feelin rough idling in my 97max auto and sluggish take off. almost felt like the engine is detonating(can't hear pings though). when the ac is on, its even worse. this just happened today. and i've been driving around 15 miles since it happened, my car felt weaker and unresponsive. the rough idling disappears if i keep it above 1k. i actually been using 87 octane but there wasn't any problems for years. i immediately filled my tank with 92s but problem persist. i'm planning on checking my sparkplugs. can anyone tell me what to expect if my engines been detonating. my car already has 105k miles. anyone had similar problems. any help or advice is greatly appreciated.

 

check your spark plug!!!

 

Possible causes include
- one or more spark coils has failed (should get SES light)
- one or more fuel injectors has failed
- vacuum leak due to damaged or disconnected vacuum line
- stuck-open Positive Crankcase Ventilation valve
- stuck-open Exhaust Gas Recirculation valve

 

Daniel,

if possible, can u tell me how to check/fix these problems if not too difficult. thanks.

 

My first guess is that you have a "dead" fuel injector. I'll give some ideas for checking injectors. If the injectors check out "good" we can move on to other possibilities.

Sound test...
This test is performed with the engine idling. Use a mechanic's
stethoscope or a length of rubber vacuum hose, and listen to each injector.
All injectors should sound alike. If you find one which makes a different
sound (or no sound at all) you have found a problem.

Resistance test...
This test is performed with the engine off. Use an ohmmeter to measure the
resistance of each injector. This does not require removing the injectors.
I don't know the correct resistance value for the injectors on your model,
but they are typically a low number such as 16 ohms. The important thing
is they should all be equal. If you find one injector with substantially
higher resistance than the others, it is bad. If you find one with zero
ohms (short circuit) that is truly unfortunate, because the injector is bad
and it may also have damaged the Engine Control Module (the computer)
because of excessive current drain.

Measuring the resistance of the front bank of cylinders is easy because the
injectors are in plain view. Disconnect the injector electrical connector
for cylinder #2, measure the resistance, reconnect the connector. Repeat
for the cylinders #4 and #6.

Measuring the resistance of the rear bank of cylinders is almost as easy,
but it is difficult to reach the injectors. The resistance may be measured
at a conveniently located electrical connector. Notice the largest,
thickest electrical harness at the top of the engine. This is the Engine
Control Harness and it is shaped like a U, with the open top of the U at the
driver's side of the car. The U has two corners. Look at the corner
nearest the passenger seat. Just inside that corner you will find an 8-pin
electrical connector. This is connector F131. Disconnect this
connector. Now look at the male part, the connector half with the pins
exposed. They are arranged in two rows of four pins.
The pins are numbered 1 - 4 (top row) and 5 - 8 (bottom row).
Measure the resistance of:
- injector #1 between pins 1 and 2.
- injector #3 between pins 1 and 6.
- injector #5 between pins 1 and 5.
Be sure to measure the PINS, not the female receptacles.

The dealer's shop is equipped with high-tech diagnostic instruments. These are wonderful devices but they are expensive and the dealer has to recover his cost by charging you for diagnostic time. Sometimes the home mechanic can do legitimate diagnostic work with nothing more than a ohmmeter and a rubber tube.

 

wow, thanks Daniel for spending the time for writing long post. I'll probably test it tonight and repost tomorrow on the outcome. hope injectors don't cost too much.

 

Using low grade octane over time will gradually ruin spark plugs quicker than normal because the computer has to adjust (retard I beleive) the timing in order to keep the car from missing/detonating. This will cause premature wear on the plugs possibly (and hopefully considering price of injectors) be your problem. If the injectors Ohm out ok, try using injector cleaner and use 91 octane or above and see if it goes away.